ALDEHYDES IN DISTILLED LIQUORS. 31 



hydrochloride, allowing the mixture to stand for a week with frequent 

 shaking, afterwards digesting it on a water bath under a reflux condenser 

 for two days and then distilling, I obtained a sample which when cooled 

 to 15° failed to give any color with rosaniline bisulphite. 



Pure aldehyde. — It was prepared by the method of McLeod. 12 This de- 

 pends upon the fact that when paraldehyde is heated with diluted sul- 

 phuric acid and distilled, aldehyde is obtained almost quantitatively. 

 The aldehyde was collected in a receiver with a known quantity of 

 water, the whole, containing 45.06 grams of aldehyde, being diluted to 

 200 cubic centimeters. 



Such a mixture keeps for a long time without polymerization. Two 

 cubic centimeters of this solution, equivalent to 0.4506 gram of aldehyde, 

 dissolved in 500 cubic centimeters of water, was regularly employed in 

 this work. 



Reagents. — The reagents are as follows : 



(a) ^ iodine. 



(b) Potassium hydrogen sulphite, about 4 grams dissolved in 100 

 cubic centimeters of water. 



(c) Starch paste. 



Determination. — For ordinary work, 25 cubic centimeters of the alde- 

 hyde solution (the strength of which must be about 0.5 per cent) are 

 mixed with 50 cubic centimeters of the potassium bisulphite in a 150 to 

 200 cubic centimeter Erlenmeyer flask. The latter is well stoppered 

 and set aside for fifteen minutes, the mixture being occasionally shaken. 

 In the meantime, 50 cubic centimeters of the potassium bisulphite are 

 titrated by the standard iodine solution, using starch paste as indicator. 

 After the expiration of the proper time, the mixture is also titrated with 

 the same iodine solution. The difference between the two titrations will 

 correspond to the bisulphite combined with the aldehyde in 25 cubic 

 centimeters of the mixture. 



Calculation. — Since one molecule of potassium hydrogen sulphite com- 

 bines with one of aldehyde, and, on the other hand, to oxidize one 

 molecule of potassium hydrogen sulphite, two atoms of iodine are re- 

 quired, the amount of aldehyde can be found from the following pro- 

 portion : 



21 M 



T= A 



Where 21 represents the iodine combining with one molecule of potas- 

 sium bisulphite ; I, the amount of iodine calculated from that of potassium 

 bisulphite absorbed by the aldehyde ; M the molecular weight of the aide- 

 hyde. and A the amount of aldehyde to be determined; hence A = ~^- 



"Am. Chem. Journ. (1907), 38, 27. 



