| Lavoisier’s experiment to determine the composition of air |
| Antoine Lavoisier performed his classic twelve-day experiment in 1779. First, Lavoisier heated pure mercury in a swan-necked retort over a charcoal furnace for twelve days. The long and curved end of the retort was inserted under a bell jar placed in a trough containing mercury. This bell jar contained a definite quantity of air. On heating the retort, a red coloured powder i.e., oxide of mercury was formed on the surface of the mercury in the retort. At the same time, mercury level in the bell jar started rising. When no more red powder was formed, Lavoisier noticed that the level of mercury in the bell jar rose to about one-fifth of the total volume of bell-jar and then became stationary. Further heating of the retort was then stopped. The remaining gas, which is 4/5 parts of the initial volume of air present in the bell jar did not support life or burning. Lavoisier called this gas ‘Azota’ (In Greek Azota means unsuitable for life), which we now call nitrogen. |
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He removed the red oxide of mercury carefully and heated it in a similar retort. He obtained exactly the same volume of gas as disappeared from the bell jar in the first experiment. He found that the gas caused flames to burn brilliantly, and small animals were active in it. Lavoisier called this gas ‘oxygen’. Finally, on mixing the two types of gas, i.e. the gas left in the first experiment (nitrogen), and that given out in the second experiment (oxygen), he got a mixture similar to air in all respects.
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Lavoisier proved by his experiment that air consists of mainly two gases called nitrogen and oxygen. And also identified that air contains 4 parts of nitrogen and 1 part of oxygen.
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