Chemistry which studies how atoms and molecules interact to form new and different substances is subdivided into various fields and one of which biochemistry studies how living organisms synthesize and use carbon and hydrogen based molecules needed for various kinds of life processes.
All the fields of chemistry depend on emphasis of precise quantitative measurements and these include measuring substances before and after a chemical reaction and this includes measuring the weights of the substances, finding the temperature if heat is released and/or absorbed, and even determining the molecular structure of the substances involved.
Chemistry, as a science, began with the work of a brilliant French scientist Antoine Laurent Lavoisier and he not only established the quantitative nature of chemistry while emphasizing the qualitative, he even did experiments involving organisms which, according to this blog, makes him the first biochemist.
Antoine Laurent Lavoiser was born in Paris, France to wealthy parents and because of his parent’s wealth, he had no trouble receiving a fine education. Originally he was meant to study law but he found science more to his taste and he pursued it with passion.
After completing his education in science, Lavoisier turned to chemistry and in the course of his experiments he emphasized careful weighing of chemical substances called reagents which are any substances before a reaction and also he weighted the products which are those after a chemical reaction.
It was his meticulous observations of accurate measurements that helped established the quantitative nature of chemistry and it was thanks to his determined effort that he had helped pushed chemistry as an quantitative science and on par with that other quantitative science, physics.
Thanks to his method of emphasizing careful weighings, he was able to solve two problems of chemistry, one involved the process of combustion and the other that water was not a chemical element as was once previously believed but a chemical compound or a combination of two or more different chemical elements.
Not surprisingly, chemistry under Lavoiser along with his British contemporaries, Joseph Priestly, who was one of the first to discover oxygen and Henry Cavendish, who isolated hydrogen was becoming a science in what is known as the chemical revolution.
Shortly after Lavoisier completed his science education, he was elected to the French Academy of Science on the grounds of excellent notes detailing his experiments and after that, his scientific researches were put to practical as well as academic use and being of noble birth, he was granted access to what was then prominent organizations prior to the French Revolution and one such organization was the Ferme générale which was a private organization that collected money for the government under France’s monarchy. Lavoisier used the money to help fund his research and because this organization was part of the government’s tax collection, this made him and others involved a target of France’s Reign of Terror and it was because of this that Lavoisier’s career in science ended when he lost his head to the guillotine.
While as a member of the French Academy of Science and the Ferme générale , Lavoiser was involved in various projects and one such project involved implementation of street lighting and Lavoiser showed no hesitation in leading the project.
To improve street lamps , which in those days before electricity, were the only source of light then, Lavoiser had to know about the process of combustion where certain substances burn releasing light and heat in the presence of gases, Lavoiser began the task of investigating combustion and through his experiments, he found that combustion involved the gas oxygen and he also found out a similar process occurring in animals but much more slowly and with less heat.
What were the steps that Lavoiser took to prove that oxygen is responsible for combustion? To understand how he arrived at that conclusion we must first emphasize that Lavoisier discovered an important principle in chemistry as well as in physics which is called the conservation of mass and this is simply that mass is always constant in a chemical reaction that is the properties of whether elements like oxygen and hydrogen may be different before and after a reaction where with oxygen and hydrogen, the result is water, the masses of the atoms remain constant.
An example to illustrate this is when wood burns and produce ashes and gas. If a piece of wood is placed in a closed vessel in the presence of oxygen and is allowed to produce ashes and gases, the wood may be different but since this reaction occurred in a closed vessel where no other gases were allowed to enter and escaped, the total amount of molecules and atoms are the same before and after. It is just that the molecules are arranged differently resulting in substances with different properties.
Lavoisier not only measured the weights of liquids and solids undergoing reactions he even measured the weights of gases. Prior to Lavoisier and beginning with ancient Greek speculation, it was thought that the matter making up the physical universe could be reduced to just four simpler “elements” which are fire, water, air, and earth.
Any combination of these resulted in the various kinds of substances we see but Lavoiser challenged this old theory and proved that “earth” is really a combination of various kinds of solid elements such as copper, iron, and sulfur and that water, which was first revealed by Lavoisier is a combination of two gaseous elements, oxygen and hydrogen.
For “proof” behind the ancient Greek idea, if a glass vessel of water is heated to boiling, some visible material may be noticed and according to the four element model, water was turning to earth. Lavoisier disproved this with his principle of mass by accurate weighing, and in an experiment where a vessel with a measured amount of water was heated for 101 days, he found that the glass vessel weighed the same before and after. Had it been true that water turns to earth, there would have noticeable changes in the vessel’s weight where the glass vessel would have a different weight after the heating.
The conclusion? The weight of the vessel was equal to the weight of the amount of visible material being released and it was from this that the visible material precipitated from the glass itself after long periods of heating.
Lavoisier challenged another theory, one that was previously put forward to explain combustion and that was the phlogiston theory.
Phlogiston theory states that substances such as wood burns because the wood is releasing a substance called phlogiston in the process of combustion and in addition, phlogiston theory was applied to the rusting of metals, or in modern terms to the formation of oxides ( this process, at the time was called “calx formation”)
As far as rusting goes, when a metal loses phlogiston, there should be a decrease in weight but when measurements are applied to rusting metals, the opposite is seen to occur. Metals gain weight but for those chemists who were working under phlogiston theory, they had to assume that phlogiston had negative weight!
Lavoisier approached this problem by first performing experiments using a combination of careful weighing and with the use of closed vessels. Before Lavoisier, phlogiston theory only created more confusion when interpreting the results regarding the increase of weight of metals after rusting (or “calxing”) and it was very likely that the confusion stem because the experiments were rather sloppy to begin with.
In 1772, Lavoisier approached the problem of combustion by first heating a sample of phosphor and he repeated the same for sulfur and found that after combustion, both solids increased in mass. The increase in mass was observed for the two metals lead and tin. How was that possible? Lavoisier came to the conclusion that since phosphor, sulfur, tin, and lead were were burning in air and not in a vacuum, and that like the sulfur and phosphour after combustion, tin and lead increased in mass , the only way to plausibly explain this was that the two metals and non metals were reacting with something in the air. Just what it was in the air that resulted in the increase in mass where the phlogiston theory should predict the opposite?
The solution to the problem occurred when doing his experiment on calx formation of tin, that the gain of weight observed occurred after Lavoiser opened the vessel. As air rushed in, the amount of mass gained resulted because of outside air rushing in! This was the case for the amount of mass observed after combustion. Recall the conservation of mass, where matter before and after a reaction is constant. If that principle is correct, then how can there be an increase of mass after the reaction? That is because when the vessel is open after burning, do you have the increase in weight.
From the conservation principle, there should be no increase in weight as well as a decrease in weight so when the vessels are closed and measured before and after, the total weight is constant and that is what Lavoisier found.
From these studies, Lavoisier concluded that combustion and calx formation or in modern terms oxide formation are the same processes since both metals and non metals produce new substances when burned in air.
What was in the air that supported both combustion and oxide formation? He proceeded to determine the composition of air and his first clue came by studying the research of two British scientists, first by the chemist Joseph Black.
Black did analysis of chemical reactions involving chalk or calcium carbonate and that after a reaction, it gave of a gas that Black called “fixed air” which is now known as carbon dioxide, an end product of combustion. In regards to fixed air , this gas is a constituent of the atmosphere and it does not support combustion. Lavoisier at first thought that carbon dioxide may explain the weight gain observed in calx formation.
Lavoisier did his experiments using closed vessels with air and metals. There was no doubt that in the presence of air, there is that weight gain but the question was , was it all of the air and some part of the air? Lavoisier came across the work performed by another British scientist, Joseph Priestly. Priestly noticed that when a sample of a substance called mercury oxide or back then, red calx of mercury, was heated to extreme temperature , it gave a gas that supported burning.
To generate this gas requires heat that was pure and more intense and Lavoisier knew this so he used magnifying glasses to generate intense heat in the course of his combustion experiments. He repeated Priestley’s work and found out that that this released gas (which Priestly under the influence of phlogiston called “dephlosgisticated air”) does support combustion.
If it was proven to support combustion then it should also support oxide formation. Lavoisier’s experiment with this gas, released from mercury oxide did support combustion and oxide or calx formation much more so than just air.
Lavoisier even gave it the name, oxygen, which in Greek meant “acid former” mainly because when he carried out combustion of phosphorous , he produced phosphoric acid, and even though we now know that not every product of combustion results in an acidic product but the name of course is still with us.
Also, he found that the fixed air of Black, was not the beginning but the end after a reaction with the fixed air or carbon dioxide the gas released after the reaction, which he observed with the red calx of mercury.
Lavoisier proved that it was this part of the air called oxygen that supports combustion and when mixed with other gases such as carbon dioxide, only the oxygen, under the influence of heat, will react with whatever substance is present whether it is wood, resulting in heat and flames or if it is a metal, rust. If these same substances were in pure oxygen, the results would be more quick and vigorous.
In 1778, after six years of rigorous research on combustion, Lavoisier summarized his findings in what is called the Easter Memoir to the French Academy of Science and this important paper detailed his careful experiments on combustion and oxide formation. These two processes are indeed related because metals, such as iron and lead, and non metals such as sulfur react with oxygen, the gas that supports combustion while nitrogen ( which Lavoisier originally called “Azote” ) and carbon dioxide ( or fixed air) did not. When wood is burned, it reacts with oxygen giving off carbon dioxide while nitrogen, another component of air, remains inert or unreactive.
Needless to say, not everyone accepted Lavosier’s findings and some thought that he may have misinterpreted the phlogiston theory. Recall that if there is such a thing as phlogiston, then in the process of burning, phlogiston goes away which means that the burnt substance should weigh less. This would also be true for oxides.
In the course of his experiments, no such decrease as well as increase in weight was observed and as long as the reactions were done in closed vessels, the mass of the reactants and products will be equal.
An experiment is as effective in proving or disproving a theory if the same experiment produces the same result, under the same conditions, if repeated in the same way many times. In time, chemists performed the same experiments and found the same results. Metals and non metals combine with oxygen. It was because of this that the phlogiston theory was disproved.
After the Easter memoir, Lavoiser turned his attention to the composition of water. It was reported that when oxygen and hydrogen ( it was called “inflammable” discovered by another British scientist, Henry Cavendish ) combines under the presence of electricity, water is formed.
Lavoisier repeated the experiment and found the same results. He also did other experiments proving that water is a chemical compound of two different gases, oxygen and hydrogen. In collaboration with the physicist Pierre Simon de Laplace, Lavoisier devised an experiment where two jets of the gases oxygen and hydrogen were allowed to react under the presence of mercury.
Another method involved passing water through a red hot metal tube where it was hot enough for a reaction with the oxygen combining with the metal forming an oxide and the hydrogen being released from another end of the tube. The observation that water can be decomposed and formed from oxygen and hydrogen was finally revealed in the presence of thirty scientists using a different set of measuring equipment which included a thermometer for measuring temperature changes, a barometer for measuring pressure, balances, and a pneumatic trough for collecting gases.
The experiment was performed by Lavoisier in collaboration with a colleague named Jean Baptist-Meusner who helped him with the red hot iron tube experiment previously. The result of the demonstration was enough to convince the skeptical colleagues the correctness regarding the composition of the water along with the final demise of the phlogiston theory.
In 1789, Lavoisier published the Elementary Treatise of Chemistry( Traité élémentaire de chimie), which is no doubt, the first textbook devoted to chemistry. Most of the chapters deals with his work on combustion but he puts emphasis on quantitative measurements which is the foundation for modern chemistry. He even introduces a nomenclature or system of naming chemical elements and an element, in the modern definition of chemistry, is any simple substance such as oxygen that cannot be broken down any further while a compound is a combination of two or more elements such as water which is a compound composed of oxygen and hydrogen.
Since oxygen supports combustion, it did not escape Lavoisier’s attention that perhaps oxygen may be responsible for animal and human life. Since I reviewed the necessary background of Lavoisier’s work, it is here in the work on combustion that lead to Lavoisier performing experiments that would rightly make him a biochemist in modern terminology.
In 1774, Priestly isolated oxygen from burning mercury oxide using a magnifying glass and found that this gas increase activity in mice. It seemed that the gas was responsible for the mice’s frantic activity.
It was known even before Priestly and Lavoisier that in addition to food and water, air is vital to both terrestrial animals and humans and if deprived of water and air, humans and land animals die. Air is then vital to the survival of many organisms.
Throughout his research, Lavoisier devised new methods and even devices to aid his investigations. In 1783, Lavoisier invented a device called an ice calorimeter which measures heat given off from any substance.
Along with Laplace, an ice calorimeter was developed which consisted of two metal cylinders nested within one another. An outer cylinder enclosed a smaller cylinder and in between was snow and in the smaller cylinder is where a chemical reaction would take place. By measuring the amount of gases such as carbon dioxide being released and also the melt water released, he could arrive at an estimate of the temperature of a combusting substance.
The ice calorimeter was put to use when Lavoisier used a healthy live guinea pig in his ice calorimeter and he estimated how much carbon dioxide and body heat realesed by the live guinea pig. He compared the results with a sample of carbon burning in oxygen and by taking into account the amount of carbon dioxide released as that of the guinea pig, Lavoisier concluded that animals do take in oxygen and give of carbon dioxide but at a much slower rate and with the release of a small amount of heat. This form of combustion, is now called respiration.
Lavoisier proceed much further with his experiments in respiration and he moved from guinea pigs to even using a human subject and once again, Lavoisier applied his rigourous method of combining accurate measurments with careful reasoning , as is the core property of science, to proving that oxygen supports animal life. It was this kind of experiment that he rightly considered a biochemist since biochemistry does depend on quantitative reasoning in formulating hypotheses and supporting theories. These experiments were carried from 1789 to 1790 but came to an end when Lavoisier was arrested, tried, and sentenced to death.
Although, it wasn’t called biochemistry then but Lavoisier proceed with the foundation of quantitative reasoning with the use of meticulous observations and accurate weighing which in the end disproved old theories such as the phlogiston theory while creating new ones such as the fact that oxygen supports combustion and respiration and without, there would be never have been an established link between oxygen and animal life and hence no biochemistry.
Antoine Lavoisier (n.d). Retrieved July 7, 2017, from https://en.wikipedia.org/wiki/Antoine_Lavoisier
Asimov, I. (1964) Breakthroughs in Science. Eau Claire, W.I. Houghton and Mifflin Company
Joseph Priestly (n.d). Retrieved July 7, 2017, from https://en.wikipedia.org/wiki/Antoine_Lavoisier
Art Gallery ErgsArt-By ErgSap’s photostream https://www.flickr.com/photos/ergsart/22327051241/in/photolist-ehCn9t-A1XYtk-rXijVx-rXkcYd-fupjDB Public Domain Mark 1.0