ALCOHOLS 67 



Tests. 



(1) Smell. Even in dilute solutions alcohol may be detected by 

 its smell. 



(2) Oxidation to Acetaldehyde. On warming a little dilute alcohol 

 in a test tube with a few drops of potassium dichromate and some 

 dilute sulphuric acid the pungent characteristic odour of aldehyde will 

 be observed and the solution turns green : 



C 2 H 5 OH + O = CH 3 . CHO + H 2 O. 



(3) Formation of Ethyl Acetate. The fruity odour of ethyl acetate is 

 produced when some of the dilute solution is heated with concentrated 

 sulphuric acid and a little solid sodium acetate. 



(4) lodoform Reaction (Lieben). About an equal volume of iodine in 

 potassium iodide is added to a very dilute solution of alcohol I or 2 

 drops in half a test tube full of water and then, drop by drop, 

 caustic soda till the mixture is decolorised. On gently warming 

 the mixture, iodoform is formed and may be recognised by its 

 characteristic smell. A yellow crystalline precipitate will separate if 

 the solution of alcohol is not too weak. 



Note. This very sensitive reaction is not characteristic of alcohol 

 as it may be given by aldehyde, acetone, acetic ester and other sub- 

 stances which contain the grouping CH 3 C joined to oxygen. 



Alcohol gives the reaction on warming, acetone gives the reaction 

 in the cold. 



Estimation of Alcohol in Beer, Wines, Spirits. 



The amount of alcohol in these liquids is ascertained by distilling off the 

 alcohol and determining the specific gravity of the distillate. 



(a) 100 c.c. beer are distilled and 80 c.c. distillate are collected. 



(b) 100 c.c. wine + 80 c.c. water and a little tannin are distilled and nearly 100 c.c. 

 distillate are collected. 



(c) 50 c.c. spirit + 100 c.c. water, or 25 c.c. spirit + 150 c.c. water, are distilled and 

 nearly 100 c.c. distillate are collected. 



The distillate is made up to 100 c.c. with water, the liquids are mixed, 

 and the sp. gr. at 15-5 or 60 F. is determined by weighing in a sp. gr. bottle. 

 The amount is given by referring to an alcohol specific gravity table for the 

 percentage by weight. The amount in the sample is ascertained from the 

 formula : 



sp. gr. of distillate x amount of distillate in c.c. x per cent, of alcohol from table 



sp. gr. of sample x amount of sample taken 

 = percentage of abs. ale. by weight in the sample. 

 If the specific gravity of the sample be unknown, it may be calculated from 



wt. of distillate x per cent, of alcohol from table 



wt. of sample taken 

 = percentage of abs. ale. by weight in the sample. 



