270 



Dr. A. Dupre on the Elimination of Alcohol. 



is transferred to a small retort, some sulphuric acid is added, and the acetic 

 acid present is distilled over. To do so effectually, the distillation is con- 

 tinued almost to dryness, some water is then added to the residue, and the 

 distillation resumed ; this is repeated three times, The distillation may 

 be conducted over an Argand burner, and sometimes it is advisable to 

 place pieces of tobacco-pipe into the retort to avoid bumping. In the 

 distillate the acetic acid is now estimated by a standard solution of deci- 

 normal soda, 1 cub. centim. of which neutralizes 0"006 grm. acetic acid, 

 and indicates therefore 0*0046 grm. of alcohol. If ordinary care has been 

 used, no trace of sulphuric acid will be present in the distillate ; but if the 

 distillation has been carried too far, so that the residue in the retort has 

 become dry, traces of sulphuric acid may have passed into the distillate. 

 In such case the acidity of the distillate is carefully estimated, and the 

 neutral solution is evaporated to dryness on a water-bath. To the dry re- 

 sidue an amount of deci- normal sulphuric acid is added slightly in excess of 

 the quantity of deci- normal soda used, and the resulting solution is once more 

 evaporated on the water-bath. During this second evaporation all the 

 acetic acid is driven off. The acidity of the residue is now determined as 

 before, and will be found equal only to the excess of deci- normal acid taken, 

 in case nothing but acetic acid (or other volatile acid) was present in the 

 distillate. If, however, any sulphuric acid had passed over, the acidity of 

 this residue will be found greater than the excess of deci- normal acid added, 

 and this surplus is the measure of the sulphuric acid contained in the dis- 

 tillate. If this then is subtracted from the total acidity originally found, 

 the rest will be the acetic acid. If an appreciable amount of volatile acid 

 is present, which to a great extent may be judged of by the colour of the 

 bichromate solution after the heating, the disturbing effect of any sulphuric 

 acid having passed over may also be neutralized in the following manner. 

 The distillate is accurately divided into two equal parts ; the acidity of the 

 one half is estimated directly, the other half is evaporated on a water- 

 bath, and the acidity of the residue left is determined. The difference 

 between these two determinations will give the volatile acid present in one 

 half of the distillate. Lastly, the acetic acid may be estimated by neu- 

 tralizing the distillate by pure barium carbonate, filtering, washing, &c, 

 evaporating the solution to dryness, and weighing the barium acetate left. 

 The above process yields accurate results, even with very small quantities 

 of alcohol ; thus in two check experiments the amount of alcohol taken was 

 0*1 and 0*025 gramme, the acetic acid obtained neutralized 20" 1 cub. 

 centims. and 5*5 cub. centims. of deci- normal soda, corresponding re- 

 spectively to 0-0924 and 0'0253 gramme of alcohol. 



Examination of Breath. — By help of a suitable mouthpiece the breath 

 is blown, through a wide tube containing chloride of calcium, into a bag 

 placed between light-pressure boards (such a bag as is used in the ad- 

 ministration of laughing-gas, and holding from 4 to 5 cubic feet). From 

 this bag it passes into a flask containing water, thence into a Liebig's con- 



