228 



MILK AND DAIRY PRODUCTS PART 



liquid is then allowed to flow out, and the drops are counted. 

 Duclaux has arranged the following table, which shows the per- 

 centage of alcohol in a liquid according to the number of drops 

 at different temperatures : 



When the amount of alcohol reaches about 15 per cent., the 

 method loses its sensitiveness, and it is then better to deter- 

 mine the specific gravity with the pyknometer. With small 

 quantities of alcohol, however, Duclaux's method is more 

 accurate than any other. Between pure water and a 1 per 

 cent, alcohol solution there is a difference of 7 drops, as may be 

 seen in the table ; the apparatus is accurate to half a drop. 

 The drawback to the method is that other volatile substances 

 which distil over with the alcohol may increase the number of 

 drops. Where great exactness is wished, both Duclaux's 

 method and that of the specific gravity can be used to check 

 one another. After the determination of the specific gravity 

 has been made, the percentage of alcohol is easily ascertained 

 from tables prepared for this purpose, and which are to be 

 found in every treatise dealing with the analysis of foods. 



As regards the testing for and estimation of other decompo- 

 sition products of milk, such as aldehyde, 1 acetone, peptone 



1 For the detection of aldehyde, see p. 232. 



