ALCOHOLS. 271 



Ethyl sulphuric acid mixed with water and distilled yields 

 sulphuric acid and ethyl alcohol : 



C 2 H 5 HS0 4 + H 2 = H 2 S0 4 + C 2 H 5 HO. 



Ethyl alcohol may also be obtained, as already mentioned, 

 by treating ethyl chloride with potassium hydrate : 



C 2 H 5 C1 + KHO = KC1 + C 2 H 5 HO. 



While the above methods for obtaining alcohol are of scien- 

 tific interest, there is but one mode of manufacturing it on a 

 large scale, namely, by the fermentation of certain kinds of 

 sugar, especially grape-sugar or glucose, C 6 H 12 6 . A diluted 

 solution of grape-sugar under the influence of certain ferments 

 (yeast) suffers decomposition, yielding carbon dioxide and 

 alcohol : 



C 6 H 12 6 = 2C0 2 + 2C 2 H 5 HO. 



Glucose. Carbon Ethyl 



dioxide. alcohol. 



By distilling the fermented liquid an alcohol is obtained con- 

 taining large quantities of water; on distilling this diluted 

 alcohol a second and third time, collecting the first portions of 

 the distilled liquid separately, an alcohol is obtained containing 

 but little water. These last quantities of water, amounting to 

 about 14 per cent., cannot be removed by simple distillation, 

 but may be separated by mixing the alcohol w r ith half its 

 weight of calcium oxide, which combines with the water to 

 form calcium hydrate, from which the alcohol may now be 

 separated by distillation. 



The alcohol thus obtained is known as pure, absolute, or real 

 alcohol. The alcohol of the U. S. P. contains 91 per cent, by 

 weight, or 94 per cent, by volume of real alcohol, and has a 

 specific gravity of 0.820 at 15.6. The diluted alcohol is made by 

 mixing equal weights of water and alcohol, and has a specific 

 gravity of 0.928. What is generally known as spirit of wine or 

 rectified spirit is an alcohol containing 84 per cent., and proof- 

 spirit one containing 49 per cent, by weight of pure alcohol. 



Pure alcohol is a transparent, colorless, mobile, and volatile 

 liquid, of a characteristic, pungent, and agreeable odor, and a 

 burning taste; it boils at 78, has a specific gravity of 0.794, is 



