ALCOHOL CHECK EXPERIMENTS. 97 



prohibited. Nevertheless, it is possible by means of determinations of 

 specific gravity and by reference to standard tables to determine with 

 great accuracy the percentage of absolute ethyl hydroxide present in a 

 mixture of alcohol and water. This procedure assumes, however, at 

 the outset that the liquid under examination contains only these sub- 

 stances. With many of the modern methods of preparing alcohol the 

 final product is frequently contaminated with alcohols of a higher car- 

 bon content. The ultimate result of the presence of these alcohols is 

 twofold. In the first place, it alters the specific gravity of the mixture ; 

 in the second place, inasmuch as the percentage of oxygen is lower, 

 the amount of carbon and hydrogen in each gram of substance is greater 

 with the higher alcohols than with ethyl alcohol. That these impuri- 

 ties are present in minute quantities in the different grades of commer- 

 cial alcohol is doubtless true, but with the grades of alcohol that we 

 have so far experimented with those ordinarily purchased from distillers 

 for use in biological and chemical laboratories we have had as yet no 

 evidence of the existence of higher alcohols in quantities sufficient to 

 influence our results. We therefore rely upon the determination of 

 specific gravity for a calculation of the amounts of carbon dioxide and 

 water that should be yielded by one gram of the alcohol. 



DETERMINATION OF SPECIFIC GRAVITY. 



By means of the pyknometer, devised and described by Squibb, 1 it is 

 possible to determine the specific gravity of a mixture of alcohol and 

 water to the fifth or even sixth decimal place. 



This pyknometer is so constructed that when immersed in water at 

 a temperature of 15.6, 50 grams of recently boiled, distilled water fills 

 the bottle and the graduated stem to an arbitrary number on the scale. 

 With the pyknometer now in use the stem is graduated from o to 70, 

 and we have found that when the level of water (bottom of the menis- 

 cus) stands at 42.5, the bottle contains 50 grams of distilled water. By 

 removing water with a small strip of bibulous paper it was found that 

 each division on the scale corresponds to a change in the weight of 

 water amounting to 1.8 mg. 



The pyknometer is first carefully dried, a very thin film of vaseline 

 applied to the ground glass stopper in the neck, and the apparatus 

 accurately weighed. The bottle is then filled with alcohol which has 

 previously been cooled in a well-stoppered bottle or flask to 10 or 12, 

 the graduated top inserted, and the bulb immersed in water at from 

 15 to 1 6. A lead collar fitting over the neck of the bottle holds it 



'Journ. Am. Chem. Soc. (1897), 19, p. in. 

 7B 



