mouse in a jar experiment

Joseph Priestley and the Discovery of Oxygen

Joseph Priestley (1773-1804)

“It is known to all persons who are conversant in experimental philosophy, that there are many little attentions and precautions necessary to be observed in the conducting of experiments, which cannot well be described in words, but which it is needless to describe, since practice will necessarily suggest them; though, like all other arts in which the hands and fingers are made use of, it is only much practice that can enable a person to go through complex experiments, of this or any kind, with ease and readiness.” — Joseph Priestley, Experiments and Observations of Different Kinds of Air (1775)

Joseph Priestley – Early Years

Joseph Priestley  was the son of a cloth maker and was born near the Oakwell Hall mansion, West Yorkshire, UK. His mother died in 1739 and the boy was adopted by his aunt, Sarah Keighley. Priestley was taught mostly at home and began studying theology and ancient languages at a nonconformist school in Daventry at the age of 19. His thinking developed from Calvinism to Unitarianism .  Around 1749, Priestley became seriously ill and believed he was dying. Priestley’s illness left him with a permanent stutter and he gave up any thoughts of entering the ministry at that time.

Later on, Priestley also studied languages including French , Italian , and  German as well as Aramic and Arabic . Also, he was introduced to mathematics , natural philosophy , logic , and metaphysics through the works of Isaac Watts , Willem’s  Gravesande , and John Locke .  In 1752 Priestley   decided to return to his theological studies and matriculated  at Daventry , a Dissenting academy and spent most of his life employed as a preacher or teacher. However, he gradually came to question the divinity of Jesus , while accepting much else of Christianity —in the process becoming an early Unitarian . [1] C onvinced that education was the key to shaping people and the world’s future, Priestley continued to support the Dissenting academies throughout his life. 

Equipment used by Joseph Priestley in his experiments on gases

Ordained Priest and Researcher

The history of electricity, the discovery of oxygen, emigration to the usa.

Around 1780 there was also a dispute with Count Shelburne, so that he moved to Birmingham . Although the conditions in Birmingham were very favorable, his theological views and political activities led to a break with his acquaintances. Priestley stood up for human rights and also upheld the ideals of the French Revolution . One of his books was burned heretically in public in 1785. Because of his advocacy of the French Revolution and several other long-standing conflicts over his person and the dissenters, the four-day Priestley Riots in Birmingham took place in 1791. Priestley lost his house with laboratory, library and numerous unpublished manuscripts He went from Birmingham to London and emigrated to the United States in 1794, where he was welcomed as a scientist and as a fervent defender of religious and political freedom. His close friends included John Adams and Thomas Jefferson . He spent the rest of his life as a writer in Pennsylvania.

References and Further Reading:

• [1] Joseph Priestley at the Chemical Heritage Foundation
• [2] Joseph Priestley at the American Chemical Society
• [3] The Discovery of Photosynthesis
• [4]  Carl Wilhelm Scheele and the Discovery of Oxygen , SciHi Blog
• [5]  Stephen Hales and the Blood Pressure , SciHi Blog
• [6]  Modern Chemistry started with Antoine Lavoisier , SciHi Blog
• [7]  Benjamin Franklin and the Invention of the Lightning Rod , SciHi Blog
• [8]  James Cook and the Great Barrier Reef , SciHi Blog
• [9] Joseph Priestley at Wikidata
• [10] Timeline for Joseph Priestley, via Wikidata
• [11]  J. Michael McBride,  19. Oxygen and the Chemical Revolution (Beginning to 1789) , Freshman Organic Chemistry (CHEM 125), YaleCourses @ youtube
• [12] Works by or about Joseph Priestley , at Wikisource

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A paradigm of fragile Earth in Priestley's bell jar

• Daniel Martin 1 , 2 ,
• Andrew Thompson 3 ,
• Iain Stewart 4 ,
• Edward Gilbert 1 ,
• Katrina Hope 5 ,
• Grace Kawai 1 &
• Alistair Griffiths 6  

Extreme Physiology & Medicine volume  1 , Article number:  4 ( 2012 ) Cite this article

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Photosynthesis maintains aerobic life on Earth, and Joseph Priestly first demonstrated this in his eighteenth-century bell jar experiments using mice and mint plants. In order to demonstrate the fragility of life on Earth, Priestley's experiment was recreated using a human subject placed within a modern-day bell jar.

A single male subject was placed within a sealed, oxygen-depleted enclosure (12.4% oxygen), which contained 274 C 3 and C 4 plants for a total of 48 h. A combination of natural and artificial light was used to ensure continuous photosynthesis during the experiment. Atmospheric gas composition within the enclosure was recorded throughout the study, and physiological responses in the subject were monitored.

After 48 h, the oxygen concentration within the container had risen to 18.1%, and hypoxaemia in the subject was alleviated (arterial oxygen saturation rose from 86% at commencement of the experiment to 99% at its end). The concentration of carbon dioxide rose to a maximum of 0.66% during the experiment.

Conclusions

This simple but unique experiment highlights the importance of plant life within the Earth's ecosystem by demonstrating our dependence upon it to restore and sustain an oxygen concentration that supports aerobic metabolism. Without the presence of plants within the sealed enclosure, the concentration of oxygen would have fallen, and carbon dioxide concentration would have risen to a point at which human life could no longer be supported.

The Earth supports a fragile ecosystem, and its inhabitants depend for their survival upon complex interactions between them, which have developed over billions of years. Imbalance of one component in this bionetwork can have far-reaching effects on organisms whose existence relies upon the presence of other species. Despite the ability to alter their environment in diverse ways, humans are reliant for their survival upon an element derived primarily from plants and produced by chlorophyll during photosynthesis, oxygen (O 2 ).

Photosynthesis is arguably the single most important chemical process on our planet, and the first colour images captured of Earth from space revealed the vast green hues of the landmasses supporting plant life, confirming its dominance within our ecosystem. Using energy from sunlight, chlorophyll strips electrons from water molecules, which then convert atmospheric carbon dioxide (CO 2 ) into carbon compounds, producing O 2 as a byproduct. Whilst mechanisms that use alternative naturally available compounds to release energy exist, the abundance of water on the surface of the Earth meant that photosynthesis rapidly became the foremost bio-energetic pathway on the planet. During the early era of chlorophyll photosynthesis, approximately 2,400 million years ago [ 1 ], the atmosphere was rich in CO 2 , whilst O 2 was scarce. As time progressed and photosynthetic species slowly overwhelmed the surface of the Earth, the concentration of O 2 rose and eventually reached levels we are accustomed to today.

In the early 1770 s, Joseph Priestley conducted a series of experiments that led to the discovery of the intimate relationship between plant and animal life [ 2 ]. In his principal experiment, Priestley placed a mouse within a sealed jar and observed it to eventually perish. When repeated with sprigs of mint within the jar, neither did the animal die ‘nor was it at all inconvenient to a mouse’ [ 2 ]. He had made the breakthrough that plants produce a substance which is life-giving to animals and then went on to describe ‘dephlogisticated air’, which, thanks to the French chemist Antoine Lavoisier, soon became known as ‘oxygen’. The story of photosynthesis was completed in 1779 when a Dutchman, Jan Ingenhousz, demonstrated that the process by which plants produce O 2 is dependent upon light.

We hypothesised that a human could survive within a sealed modern-day bell jar, even if the O 2 concentration within was significantly reduced from the outset, provided that it contained sufficient plant matter to generate O 2 and remove CO 2 via photosynthesis.

Formal ethical approval was not sought for this experiment as it was designed for the purpose of a television demonstration; consent was implied through the subject's involvement in the project and participation in the event. The Chair of the University College London Committee on the Ethics of Non-NHS Human Research approved this strategy. Prior to commencing the experiment, a full medical screening questionnaire was completed by the subject, and he was assessed by a physician with experience in high altitude and acute hypoxia research (DM). The protocol was explained to the subject in full, along with a description of the potential risks and safety measures in place. A standard resuscitation kit was available throughout the experiment, along with bottled supplemental oxygen. A physician trained in Advanced Life Support was also present outside the container throughout the experiment, with the ability to enter the container at any point should there be concerns regarding the welfare of the subject.

We constructed the first human recreation of Priestley's ‘mouse in a bell jar’ experiment to demonstrate the ability of plants to generate sufficient O 2 to sustain human life in an enclosed environment [ 3 ]. A healthy 47-year-old male was placed within a transparent airtight container measuring 2.0 × 2.5 × 6.0 m (30 m 3 , Figure 1 ), itself placed within the rainforest biome at the Eden Project, Cornwall, UK. A selection of plants known for their high photosynthetic yield (under certain environmental conditions) was placed within the container. Prior to the experiment, containerised plants were grown in a peat-free Eden Project Melcourt mix within a standard glasshouse at a relative humidity of 70% to 80% and temperature range of 15°C to 30°C. During this growing phase, the plants were watered with liquid nutrient feed at 20 ml/L (N 177 ppm, P 35 ppm, K 119 ppm, Ca 49 ppm, Mg 17 ppm, B 0.2 ppm, Cu 0.08 ppm, Fe 1.44 ppm, Mn 0.48 ppm, Mo 0.04 ppm and Zn 0.64 ppm). In total, 274 plants consisting of 18 different taxa were placed within the container, with 10,967 leaves (excluding Tillandsia usneoides ) and a total leaf area of 1,106,033 cm 2 (Table 1 ). A mixture of C 3 (ribulose diphosphate carboxylase utilising) and C 4 (phosphoenolpyruvate carboxylase utilising) plants were selected in order to maximise photosynthetic potential within the container. Several C 4 carbon fixation plants were grown, including Miscanthus x giganteus and Zea mays (maize), because they have advantages over C 3 plants, resulting in superior carbon-gaining capacities and photosynthetic efficiency [ 4 ]. During the experiment, the subject regularly irrigated the plants when deemed necessary from a water source within the container.

The sealed container with plants, the subject and external artificial lighting.

In order to more clearly demonstrate oxygen production and highlight the effectiveness of photosynthesis in preserving human life, the environment within the container was rendered hypoxic at the start of the experiment. Three hypoxic generators (Hypoxico Everest Summit II, Hypoxico Inc, New York, NY, USA) were used to reduce the concentration of O 2 in the container. These devices consist of a molecular sieve system that uses zeolite to separate nitrogen from O 2 in the air and consequently provides a nitrogen-rich gas mixture to purge the atmosphere within the container. Connected to the container, and in conjunction with a one-way pressure relief valve, the hypoxic generators reduced the concentration of O 2 to 12.4% prior to commencing the experiment. Once the subject was sealed inside the container and safety procedures had been confirmed, the hypoxic generators were switched off and the one-way valves were closed. Artificial lighting (8 × 2,000 W systems; ARRI, Munich, Germany) was placed around the container externally and switched on at the beginning of the experiment. A split air-conditioning unit (Clima 16 HP Portable Air Conditioner, Toshiba, Tokyo, Japan) was used to maintain temperatures for optimal plant growth and comfort for the subject whilst ensuring a sealed atmosphere. The concentrations of O 2 and CO 2 within the container were monitored with a gas analyser (Aspida, Analox, London, UK) and plotted every hour along with temperature and humidity from a digital hygro-thermometer (Brannan, Cumbria, UK). The subject's heart rate and arterial O 2 saturation (SpO 2 ) were monitored continuously (Johnson and Johnson Dinamap MPS Monitor and Onyx 9500, Nonin, Plymouth, MN, USA); respiratory rate was recorded hourly by manual calculation.

The concentration of O 2 in the container rose throughout the experiment, peaking at 18.1% in the final hour (hour 48; Figure 2 ). The CO 2 concentration fluctuated depending on the subject's activity within the container (declining noticeably during sleep), but there was an overall rise that peaked at 0.66%, approximately halfway through the experiment (Figure 3 ). There was a diurnal variation in temperature (25.3°C to 28.4°C), and humidity varied between 57% and 87%. On entering the hypoxic container, the subject had a heart rate of 90 beats per minute, respiratory rate of 20 breaths per minute and SpO 2 of 86%. These figures returned to the subject's resting normal values as the concentration of O 2 rose within the container. The subject's final SpO 2 was 99% (Figure 4 ).

Change in oxygen concentration within the container over time.

Change in carbon dioxide concentration within the container over time. The shaded areas are those during which the subject was sleeping.

Changes in the subject's oxygen saturation and heart rate during enclosure within the container.

The design of the biological ecosystem in this study was such that human life was sustained for 48 h and the initial hypoxic environment restored to one of near-normal O 2 concentration. In the early 1990's, the ‘Biosphere 2’ experiment was conducted to explore the feasibility of self-sustaining biospheres in space. This grand design consisted of a 200 m 3 atmosphere within a dome that contained eight volunteers, which was designed to sustain them for 2 years [ 5 ]. However, the O 2 concentration within the biosphere dropped from 20.9% to 14.2% after 16 months, so additional O 2 had to be added to the atmosphere [ 6 ]. This decline was traced to a two-step process: firstly, there was O 2 loss to organic soil matter producing CO 2 , and secondly, the CO 2 was being captured by structural concrete to form calcium carbonate [ 5 ]. In the current experiment, the initial O 2 concentration of 12.4% (equivalent to approximately 4,500 m above sea level) resulted in a marked reduction in the subject's SpO 2 and represents an acute hypoxic exposure that is frequently associated with symptoms of altitude-related illness [ 7 ]. During the last few hours of the study, there was a small reduction in rate of the O 2 concentration rise, perhaps due to deterioration in the condition of the plants, noticeable towards the end of the experiment. Direct heating and excessive light exposure, arguably both present in this experiment, can lead to the denaturing of enzymes within chlorophyll [ 8 ]. There were fluctuations in CO 2 concentration throughout the study, with a tendency for it to rise as time progressed (Figure 3 ).

As well as providing an insight into the use of plants to maintain a self-sufficient biosphere, such as would be required on the surface of extra-terrestrial bodies without an atmosphere, our experiment highlights the detrimental effects of a markedly increased CO 2 concentration. CO 2 concentrations have altered dramatically over the course of the Earth's history [ 9 ], and there is much concern that levels are now rising at an alarming rate [ 10 ]. Under certain environmental conditions, increasing the ambient concentration of CO 2 can be beneficial, increasing photosynthetic activity, plant growth and yield [ 11 , 12 ]. Using CO 2 enrichment to increase plant growth and yield is now commonplace in commercial glasshouse crop production, with optimal levels being between 700 and 1,000 ppm [ 13 ]. However, in some species, super-elevated CO 2 concentrations (over 2,000 ppm) induces foliar symptoms of chlorosis and necrosis [ 14 , 15 ], and levels above 10,000 ppm are known to cause damage to young maize plants after 48 h in the form of ‘yellow streaks’ [ 16 ]. During this experiment, the CO 2 levels remained above 2,000 ppm and reached a maximum of 6,600 ppm, yet yellow streaks were observed on the maize plants by the end. It is possible that damage to the maize may have also reduced the photosynthetic yield and the production of O 2 towards the end of this experiment. This study, therefore, provides an insight into the use of plants to maintain a self-sufficient biosphere, such as would be required on the surface of extra-terrestrial bodies without an atmosphere, and the potentially detrimental effects of a dramatically increased CO 2 concentration.

This simple experiment is a humble reminder of the integral relationship between animal and plant life on Earth, in which the former owe their existence to the latter. Without the presence of plants within the sealed environment, the concentration of O 2 would have fallen and CO 2 concentration would have risen to a point at which human life could no longer be supported. Whilst O 2 sustains human life and plants maintain its level within the atmosphere with remarkable efficiency, the fundamental role of photosynthesis is arguably taken for granted. Deprived of plants, the subject within the container would have succumbed to the effects of severe hypoxaemia. The experiment reminds us of our total dependency upon plants, and the ecosystem in which they exist.

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Acknowledgements

We would like to thank the BBC Scotland team for the ‘How to Make a Planet’ series and all the staff at the Eden Project in Cornwall who made this experiment possible.

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Andrew Thompson

School of Geography, Earth & Environmental Sciences, Plymouth University, Plymouth, PL4 8AA, UK

Iain Stewart

Centre of Human & Aerospace Physiological Sciences, School of Biomedical Sciences, King's College London, London, SE1 1UL, UK

Katrina Hope

The Eden Project, Bodelva, Cornwall, PL24 2SG, UK

Alistair Griffiths

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Correspondence to Daniel Martin .

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The author declares that they have no competing interests.

Authors’ contributions

AT conceived the idea, and the experiment was designed by AT, AG and DM. The experiment was conducted by DM, KH, EG, GK, AT and IS. Data were analysed by DM, and the manuscript was written by DM, AG and EG. All authors discussed the results and implications and commented on the manuscript at all stages. All authors read and approved the final manuscript.

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Martin, D., Thompson, A., Stewart, I. et al. A paradigm of fragile Earth in Priestley's bell jar. Extrem Physiol Med 1 , 4 (2012). https://doi.org/10.1186/2046-7648-1-4

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Discovering Oxygen: A Brief History

Because there are three different dead guys who regularly vie for credit for discovering oxygen, we’ve staged a little friendly competition to establish which of these great men deserves the title of the O-master. In evaluating the contenders, we’ll look at when they isolated oxygen and how their experiments furthered our understanding of the element. In addition to bragging rights, the winner takes home one zillion liters of oxygen.

Contender 1: Carl Wilhelm Scheele

Nationality: Swedish Occupation: Apothecary

Biggest Accomplishment: In 1772, he was the first person to figure out a way – actually a couple of ways - to isolate oxygen. He discovered that mercuric oxide, silver carbonate, magnesium nitrate, and potassium nitrate all gave off the same gas when heated. Scheele dubbed the mystery element “fire air” because he noticed that it produced sparks when it came into contact with charcoal dust.

Other Biggest Accomplishment: Discovered chlorine

Biggest Shortcoming:

Bad timing. Scheele didn’t publish his discovery until 1777, in a treatise called Chemical Observations and Experiments on Air and Fire . By that time, Joseph Priestley had already written a paper describing his findings and published the comprehensive Experiments and Observations on Air . Lavoisier had also successfully isolated the gas. Because Scheele waited so long to get the word out, his groundbreaking experiment was often overlooked by other scientists, earning him the nickname “Hard Luck Scheele.”

Contender 2: Joseph Priestley

Nationality: British

Occupation: Radical Unitarian Minister

Biggest accomplishment: In 1771, Priestley noticed that a mouse in a sealed jar would eventually collapse. He then tried slipping a sprig of mint inside and realized the plant magically revived his subject. Realizing that plants did something to freshen up the air, he wrote to his friend Benjamin Franklin, saying he hoped his discovery would stop people from cutting down so many trees.

Priestley didn’t actually isolate this mystery gas until August 1, 1774, when he heated some mercuric oxide powder and discovered that it gave off a gas that could reignite a glowing ember. He collected large amounts of the gas and tried breathing it himself. After a few puffs, Priestley was hooked. He declared, “My breast felt peculiarly light and easy for some time afterward.”

Other Biggest Accomplishment: Invented seltzer water

Biggest Shortcoming: Priestley just wouldn’t let go of phlogiston theory – a crackpot hypothesis that argued combustion was fueled by an invisible substance called phlogiston. Priestley believed that his mystery gas supported combustion because it was pure and could absorb phlogiston released by burning substances. That’s why he was pushing to name oxygen “dephlogisticated air.”

Contender 3: Antoine Laurent Lavoisier

Nationality: French

Occupation: Tax farmer/Commissioner of the Royal Gunpowder and Saltpeter Administration

Biggest Accomplishment: Lavoisier debunked phlogiston theory. Up until then, scientists couldn’t explain why tin gained weight when it was burned; if it was releasing phlogiston, it should lose weight. Lavoisier realized that there was no way phlogiston could have a negative mass and set out to prove that combustion was caused by something else. He heated Mercury until calx formed, then he heated the calx until it gave off a clear gas. Lavoisier realized combustion resulted from a chemical reaction with this gas – not some flammable mystery element called phlogiston. He dubbed the gas “oxygen” – a name that referred to its ability to create acids.

Other Biggest Accomplishment: Helped establish this thing called the metric system, which some people supposedly use.

Biggest Shortcoming: Lavoisier might have been the one to name oxygen, and for that, we’re grateful (nobody would be caught dead in a dephlogisticated air bar). However, he was not the first to isolate the gas or recognize its unique properties. His methods weren’t even original. In fact, Lavoisier had been in contact with both Priestley and Scheele and borrowed from their experiments.

And the O-Master Is...

We’re giving this one to Joseph Priestley. Although he gets points for publishing first, his real breakthrough was his realization that plants gave off oxygen. This discovery enabled future scientists to understand cellular respiration and photosynthesis – both of which are absolutely essential to life on Earth. We’re also giving Priestley points for recognizing the commercial potential of oxygen when he anticipated that the pure air could be a hit at parties. Sure enough, over 200 years later, oxygen bars have become a thing!

So next time you take a breath (hopefully soon), think of Joseph Priestley and his iconic experiment, which took place exactly 238 years ago today.

Discovering Nitrogen: Rutherford’s Jar Experiment

Concept Introduction

Rutherford’s nitrogen experiment and discovery was in the late 1700’s. He performed experiments to prove that he had isolated a new element.

Rutherford Suggests the Existence of Nitrogen 

200 years ago , a scientist discovered an invisible, odorless, and colorless gas. Chemists at the time propagated the theory of phlogiston. According to the theory, all flammable substances contained a “phlogiston”–a material released upon combustion. Phlogistons were also invisible, odorless, and colorless. These similarities contributed to nitrogen’s existence being overlooked. But Daniel Rutherford (1749-1819), a Scottish chemist, physician, and botanist, explored the overgeneralized theory. He investigated more acutely what really composed these “phlogistons.” 

Experimentally Isolating Nitrogen 

Rutherford postulated the existence of a gas that does not catalyze combustion reactions . This inability set it apart from the other components of our atmosphere, such as oxygen and carbon dioxide. He explored this hypothesis by conducting an experiment in 1772 that facilitated the isolation of this gas. His test included discrete steps that eliminated oxygen and carbon dioxide from a gaseous sample. 

Rutherford’s Nitrogen Experimental Steps:

• Placing a living mouse inside a closed glass jar until it expired. 
• Burning a candle in the same jar until its flame died. 
• Burning solid phosphorus in the jar until it, too, stopped burning. At this point, he had removed all of the oxygen from the gaseous sample; the mouse, candle, and phosphorus had consumed this oxygen and, in turn, produced carbon dioxide. 
• Passing the remaining air from the jar through a solution that absorbed this carbon dioxide via chemical reactions, thus removing it from the gaseous sample. 

Unpacking Rutherford’s Nitrogen Experiment Conclusions

His experimental successes.

Upon removing all oxygen and carbon dioxide from his initial sample of gas, Rutherford was left with what he dubbed “noxious” air. He employed this term to convey the fact that the mouse, and by association, living organisms, could not live in it. Nor could substances combust in it. But while he had successfully isolated nitrogen gas , his subsequent inferences regarding its identity as “phlogisticated air” proved incorrect. 

His Experimental Shortcomings

Rutherford deduced, based off of the theory of phlogiston, that his noxious gas must have played a compositional role as a phlogiston substance. He bolstered this assumption by noting that the substance was “left over” from the combustion reactions. Thus, while it had not necessarily catalyzed the burning of the candle or phosphorus , its presence at the end of the experiment reflected the expected behavior of a phlogiston.

In the late 1770s, French chemist Antoine Lavoisier, a great scientist , disproved the theory of phlogiston by introducing his findings regarding oxygen combustion. Essentially, Lavoisier pointed out that pro-phlogiston chemists could not account for weight changes that occurred during combustion reactions, given that fire itself could not be weighed. As decades passed, phlogiston became regarded more as a principle as opposed to a physical substance; eventually, its overcomplication and overly assumptive nature contributed to its demise. But while the theory thus cannot be applied to Rutherford’s findings, accounting for Lavoisier’s ideas supports the elimination of oxygen that occurred during the combustion reactions, which led to the ultimate, successful isolation of the “noxious gas.”

Nitrogen as an Element

Around 1800, scientists coined the word “nitrogen.” This term stems from the French words “nitre” and “gène,” which combine to convey nitrogen’s status as a key constituent of nitric acid (learn how nitric acid helped discover molybdenum ). Today, we know that nitrogen is the most abundant element in Earth’s atmosphere. It is present in all living matter. 

This element has proven crucial to life on our planet. Nitrogen compounds exist in everything from fertilizers to explosives. They constitute nearly all organic materials and food items. So while we have Rutherford to thank for distilling nitrogen and demonstrating its non-flammable nature, its identity, value, and traits are far more intricate than this single property.

Further Reading

Discovering the Nucleus: Rutherford’s Gold Foil Experiment Phase Diagrams Producing Oxygen (On AmazingRust)

• Biology Article
• Photosynthesis Early Experiments

Early Experiments on Photosynthesis

Table of contents, introduction, photosynthesis discovery – early experiments, experiment to prove carbon dioxide is essential for photosynthesis, other experiments.

Photosynthesis is a light-dependant process that plants use to produce their own food. It is the process by which plants convert light energy into chemical energy, which can be used later for plants’ own processes. During this process, oxygen is produced as a byproduct. Photosynthesis was discovered only in 1800. To prove the existence of photosynthesis in plants, many scientists performed numerous experiments.

Let us have a detailed look at the early experiments on photosynthesis.

Also Read:  What is Photosynthesis

Since photosynthesis is a light-dependant process, it only takes place in the presence of sunlight. But along with sunlight, the plant also requires water and carbon dioxide as raw materials for this process to synthesise carbohydrates. Green plants also possess a green pigment known as chlorophyll which helps in capturing light energy. All these key features of photosynthesis were revealed later during the mid-nineteenth century when numerous scientific studies were conducted on photosynthesis.

Below mentioned are the experiments that were conducted by the early scientists in support of photosynthesis.

Materials required: A healthy potted plant, a wide-mouthed glass bottle with a split cork, potassium hydroxide solution (KOH), and starch solution.

Experiment:

• Select a healthy potted plant and place it in the darkroom for two to three days to ensure the leaves are free from starch.
• In a wide-mouthed glass bottle, add 10-15 ml of potassium hydroxide solution and split the cork vertically.
• Now carefully insert half part of a leaf into a glass bottle through the split cork and the other half exposed to air.
• Place the complete unit undisturbed in sunlight for about 3 – 4 hours.
• After 4 hours, detach the leaf from the plant and slowly remove it from the bottle and test it with the starch solution.
• We can observe that the half part leaf which was inside the glass bottle (KOH solution) did not show any colour change, but the other half part exposed to the surroundings turned its colour to dark brown, indicating the presence of starch in it.

Conclusion: In this experiment, we can conclude that carbon dioxide is essential for photosynthesis. Both the portion of the leaf received the same amount of water, chloroplasts , and sunlight but the half part which was inside the glass bottle did not receive carbon dioxide.

After discovering the importance of carbon dioxide in photosynthesis, many experiments were conducted to understand other essential factors for this process. Joseph Priestly was one of the first scientists to perform these experiments.

Experiment by Joseph Priestley

In 1770, after a series of experiments, Joseph Priestley came to a conclusion regarding the essentiality of air for photosynthesis and also for the growth of plants.

Materials required: A bell jar, candle, rat, and a plant.

• Priestley kept a burning candle and a rat together in the single bell jar.
• After some time, the candle was extinguished, and the rat died.
• For the second time, he kept a burning candle, a rat, and a green plant together in the bell jar.
• He observed that neither the candle got extinguished nor did the rat die.

Conclusion: Based on his observations, Priestley concluded that in the first case, the air in the bell jar got polluted by the candle and rat. However, in the second case, the plant reinstated the air that was spoiled by the candle and the rat.

But it took another few years to reveal what was exactly released by the plant to keep the rat alive and the candle burning.

Jan Ingenhousz: He proved that sunlight is essential for the photosynthesis process during which carbon dioxide is used and oxygen is produced.

Jean Senebier: He demonstrated that during photosynthesis, carbon dioxide in the air is absorbed, and oxygen is released by the plant.

Julius Robert Mayer: Mayer proposed the idea that light energy is being converted into chemical energy during photosynthesis.

Julius Von Sachs: He discovered that the photosynthesis process leads to the production of glucose molecules.

T.W.Engelmann: Engelmann was the scientist who discovered the importance of chlorophyll in photosynthesis.

Cornelius van Niel: He introduced the chemical equation of the photosynthesis process when he revealed that the oxygen released by plants at the end of photosynthesis comes from water and not from carbon dioxide.

Also Read:  Photosynthesis in Higher Plants

To learn more about the photosynthesis discovery and early experiments on photosynthesis, keep visiting BYJU’S website or download BYJU’S app for further reference.

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Are any experiments that had been done but related to other factors which affecting the rate of photosynthesis?, If so then I would be grateful if you can send me any of them. I am very interested to do such experiment and that will be also a part of my assessment task that I will be doing next week. Most of the information that I get from the source really help me, and I hope that it is vital for me.

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Drowning Rats Psychology Experiment: Resilience and the Power of Hope

In the 1950s, Curt Richter, a professor at Johns Hopkins, did a famous drowning rats psychology experiment. This experiment, though cruel, demonstrated the power of hope and resilience in overcoming difficult situations. Summary by The World of Work Project

A Psychology Experiment: Drowning Rats

In a series of experiments that are fairly cruel and unpalatable, yet interesting in their findings, Curt Richter demonstrated that hope is a powerful factor in perseverance. In our view, this is also closely linked with resilience .

The Drowning Rats Psychology Experiments

Curt’s experiments focused on how long it takes rats to die from drowning. He conducted his experiments by placing rats into buckets filled with water and seeing how long they survived. He introduced a range of variables into the experiment, that yielded some interested results.

Domesticated Rats

12 domesticated rats were used in Curt’s first set of experiments. The first of these rats initially swam around the surface, then dove to the bottom of the bucket and explored what was there for a while. It lasted a total of two minutes before it drowned.

Two of the other domesticated rats did roughly the same thing, and survived for roughly the same period of time.

The other nine domesticated rats though did something completely different. After an initial exploration, the predominantly spent their time and the surface. And the just kept swimming. They survived for literally days before eventually succumbing to exhaustion and drowning.

The second set of experiments Curt undertook involved 34 wild rats. Wild rats are excellent swimmers, and these savage and aggressive ones had only recently been caught. Obviously, Curt expected them to fight hard for their survival.

Surprisingly though, this wasn’t the case at all. Despite their ferocity, fitness and swimming ability, not one of the 34 wild rats survived more than a few minutes.

The Role of Hope

Curt reflected on what caused some of the rats to give up and decided that hope a key factor in the willingness to struggle on. Where rats have perhaps been helped in the past and have hope of being saved, they will keep fighting in the believe that all is not lost. However, when they don’t have this prior experience, they will give up quickly.

In his own words he said: “ The situation of these rats scarcely seems one demanding fight or flight — it is rather one of hopelessness… the rats are in a situation against which they have no defense… they seem literally to ‘give up.’ ”

With this in mind, Curt decided to experiment further.

Introducing Hope and Support

The last set of experiments that we’ll focus on were concerned with the impact that introducing hope would have on the perseverance of the rats in buckets. In these experiments Curt’s hypothesis was roughly that introducing hope to rats would increase their survival times.

To test his hypothesis Curt selected a new cohort of rats who were all similar to each other. Again, he introduced them into buckets and observed them as they progressed towards drowning. This time though, he noted the moment at which they gave up then, just before they died, he rescued them. He saved them, held them for a while and helped them recover.

He then placed them back into the buckets and started the experiments all over again. And he discovered that his hypothesis was right. When the rats were placed back into the water they swam and swam, for much longer than they had the first time they were placed in the buckets. The only thing that had changed was that they had been saved before, so had hope this time.

Curt wrote that “ the rats quickly learn that the situation is not actually hopeless ” and that “ after elimination of hopelessness the rats do not die .”

What This May Mean For People

Humans and rats are very different beings, but there is still a belief that we can learn a lot from these experiments. Where individuals have hope, they have higher levels of perseverance. They will keep fighting when they feel these is a chance of success or rescue. When they don’t have hope, they won’t.

A range of other experiments have also supported this.

What This Means in the World of Work

From a work perspective, these findings can be taken to mean that people will remain resilient and will continue to persevere in the face of difficult situations, provided they have hope.

So, if they are rescued from time to time. If they are supported. If they believe the future will be a better place and if they feel others are there to help them, they may be able to drive themselves through difficult situations. The importance of belief here is similar to the importance of belief in the expectancy theory of motivation .

What this means for leaders is that people in your team will be strong and resilient, provided that you give them hope of a better future. If that hope is extinguished, your people will stop fighting for you.

Some Specific Quotes from Richter

“The situation of these rats scarcely seems one demanding fight or flight—it is rather one of hopelessness; whether they are restrained in the hand or confined in the swimming jar, the rats are in a situation against which they have no defense. This reaction of hopelessness is shown by some wild rats very soon after being grasped in the hand and prevented from moving; they seem literally to ‘give up’. Support for the assumption that the sudden death phenomenon depends largely on emotional reactions to restraint or immersion comes from the observation that after elimination of the hopelessness the rats do not die. This is achieved by repeatedly holding the rats briefly and then freeing them, and by immersing them in water for a few minutes on several occasions. In this way the rats quickly learn that the situation is not actually hopeless; thereafter they again become aggressive, try to escape, and show no signs of giving up. Wild rats so conditioned swim just as long as domestic rats or longer.” You can find these comments on p196 of this pdf .

Learning More

Our resilience can be an important factor in our Wellbeing in the workplace. It’s a bit of a difficult concept to pin down, but we can get a sense of how resilient we are with the Brief Resilience Scale .

There are steps we can take to improve our own wellbeing . Improving our self-awareness might also help us improve our wellbeing. Similarly, learning about different types of stress and how to manage stress can be helpful. The below podcast covers the concept of stress-buckets, which might of interest.

The World of Work Project View

These drowning rats psychology experiments are clearly abhorrent, as is most animal testing. We know that the findings of many experiments do not translate to humans. In fact, experiments of this nature are still being used by several organizations. This should stop. A good starting point for finding out which organizations still use this form of testing so that you can avoid their products is this article by PETA .

Though these experiments should no longer take place, we shouldn’t ignore what people have already discovered from them in the past. The findings from these experiments are interesting. The fact that hope leads to greater resilience comes as little surprise to us, though of course findings in rats may not translate to other species. That said, we think this is probably the case in humans as well as rats.

In fact, we believe that a large part of the role of leadership is to help individuals feel valued, respected, supported and hopeful about their futures. In doing this, individuals can have better qualities of working life, and organizations can have higher levels of productivity.

That said, we think these experiments and the lessons that can be learned from them are also very sinister. It’s clearly the case that providing people with hope, real or false, inspires them to greater effort. We are certain that many organizations and HR functions know this, and look to build this into their management approaches.

Where hope is real, it’s good. Where it’s falsely introduced to drive individuals to higher levels of perseverance in poor working situations, then it’s quite reprehensible. Which doesn’t mean it’s not profitable or that it doesn’t happen. It just means that people should not work for these organizations where they have any choice.

Interestingly, the relationship between hope and faith has been discussed many times throughout history. A good place to listen to some reflections on this is in this episode of the BBC podcast “In Our Time”.

How We Help Organizations

We provide leadership development programmes and consulting services to clients around the world to help them become high performing organizations that are great places to work. We receive great feedback, build meaningful and lasting relationships and provide reduced cost services where price is a barrier.

Learning more about who we are and what we do it easy: To hear from us, please join our mailing list . To ask about how we can help you or your organization, please contact us . To explore topics we care about, listen to our podcast . To attend a free seminar, please check out our eventbrite page .

We’re also considering creating a community for people interested in improving the world of work. If you’d like to be part of it, please contact us .

Sources and Feedback

Schulkin, Jay, and Paul Rozin. Curt Richter: A Life in the Laboratory. Baltimore: Johns Hopkins University Press, 2005., doi:10.1353/book.60340. https://www.aipro.info/wp/wp-content/uploads/2017/08/phenomena_sudden_death.pdf

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Learn Something Interesting

Education for the pure joy of learning, the harvard university hope experiment.

During the 1950’s, Dr. Curt Richter from Harvard University performed a series of experiments using water, buckets, and both domesticated and wild rats which resulted in a surprising discovery within the field of psychology. In the first experiment, Richter placed his test subjects into large buckets half filled with water with even those rats which were considered above average swimmers, giving up and dying within a few short minutes. In the second experiment, Richter pulled each rat out just as it was about to give up due to exhaustion and let them rest for a few moments. Upon inserting the rats back into the bucket of water, Richter found that the rats continued to struggle to survive for up to 60 hours as the rats now believed that if they continued to push forward with enough effort put forth, eventually they would be rescued once again. Richter recorded in his notes, “after elimination of hopelessness, the rats do not die”

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I’m a great swimmer and I hate rats…what does that make me?

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Thanks! I will now visit this blog every day!

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