Oil Analysis & Fermentation
From WikidChem
[edit]Elemental Analysis by Oil Combustion
Lavoisier used this technique to analyze compounds that burn cleanly.
The large bucket on the left-hand side was inverted over water to provide an air supply. The tubing below the bucket provided a second air supply so the flame was kept alive.
- The compound being analyzed WAS the oil, nothing was added to it, except the oxygen in air with which it was to react. Different oils could have been used, but none were, because there is no record of the machine actually having been used. The French Revolution intervened and Lavoisier was guillotined. Your idea of mixing something else with the oil for purposes of analyzing them together is a reasonable one, but not what anyone did. Improved methods with better oxidizing agents came first. - JMM
Lavoisier collected the resulting water with a desiccator and carbon dioxide in flasks containing aqueous base and a stirrer. Some water in these flasks would have escaped into the gas phase; Lavoisier placed a second desiccator after the CO2 collector to account for this.
The amount of carbon was determined from the amount of CO2 and the amount of hydrogen from the H2O in the first desiccator. Because oxygen appears in both products, its amount was figured out by subtracting the resulting carbon and hydrogen from the initial weight of the compound.
[edit]Elemental Analysis by Fermentation
Not all compounds burn cleanly into CO2 and H2O; they char instead. An example of this is grape sugar. Rather than burning these substances to figure out their elemental makeup, Lavoisier fermented them.
The large round-bottomed flask on the left contained grape sugar, water, and yeast; this is where fermentation took place. As the mixture fermented, CO2 bubbles (mixed with some water and other gases) formed and rose to the top of the flask's neck. Water was first removed from the CO2 using a desiccator (containing CaCl2). CO2 was then absorbed by a base, in this case NaOH. Any leftover gases were bubbled through mercury and trapped under a bell jar.
Of course, when the reaction had finished, there were still sugar, water, yeast, and alcohol left in the round-bottomed jar. Lavoisier needed to distill these components before he could calculate the amounts of C, H, and O in the grape sugar.
