32 ORGANIC AGRICULTURAL CHEMISTRY 



evaporating dish or watch glass. Remember alcohol volatilizes com- 

 pletely. What is the residue like? It is known as sodium ethylate 

 and has the composition C2H50Na. By quantitative determination 

 it has been proven that only one hydrogen is replaced by sodium. 

 This proves that one hydrogen is combined as in water in the form 

 of hydroxyl (—OH). 



(4) Test for ethyl alcohol. Prepare two solutions of ethyl alcohol 

 in water approximately i.o per cent and o.i per cent strength. (95 

 per cent alcohol i.o c.c. + water 99 c.c. = approximately i.o per cent 

 alcohol. 1.0 per cent alcohol lo.o c.c. + water 90 c.c. = approxi- 

 mately 0.1 per cent alcohol.) Test each of the solutions as follows: 

 — Take 10 c.c. of the dilute alcohol in a test tube. Add two or three 

 small crystals of iodine. Add 5.0 c.c. dilute KOH or NaOH. Warm 

 the mixture. A yellow crystalline precipitate giving the odor of 

 iodoform is proof of the presence of alcohol in the original solution. 

 Dilute the o.i per cent solution 10 times, and repeat the test. 



(5) Test for water in ethyl alcohol. To 5.0 c.c. of 95 per cent ethyl 

 alcohol add about i g. of anhydrous copper sulphate. Shake and 

 let stand. Note change in the copper sulphate. Anhydrous copper 

 sulphate is almost white. When it takes up water it is converted 

 into the ordinary copper sulphate which is blue and has 5 H2O as 

 water of crystallization, (CUSO4 . 5 H2O). If in the test the copper 

 sulphate remains white, the alcohol has no water, i.e. it is absolute 

 alcohol. If water is present even in small proportions, the copper 

 sulphate will turn blue. 



Alcoholic Fermentation. — It was early discovered that when 

 the juice of grapes and other sweet fruits was allowed to ferment 

 it took on a sharp taste and affected the body in a stimulating 

 manner. This property was found to be due to the presence of 

 alcohol in the fermented liquid. In 1836 Cagniard de la Tour 

 and von Schwann showed that the alcohol in such fermentation 

 was produced by the action of a living plant organism upon 

 sugar solutions. This organism is the common yeast plant, 

 Saccharomyces cerevisice. Liebig held the view known as the 

 mechanical chemical theory of fermentation according to which 

 the action was due to some catalytic substance. The views of 

 von Schwann and de la Tour were later thoroughly established 

 by the work of Pasteur, and it became an accepted idea that 



