SOUR MILK. 201 



milks has varied from 0-32 per cent, above the solids not fat 

 in the original milk to 0-20 per cent, below, and to average 

 0-06 per cent, above. The determinations on the original milks 

 were made by subtracting the fat by Gottlieb's method from the 

 total solids by evaporation. With milks in which no very large 

 amount of volatile acid was developed the figures were -j- 0-17, 

 0*19, and -}- 0-07 respectively. At the Government Labora- 

 tory only corrections Nos. 1, 2, and 5, and, if necessary, a correc- 

 tion of 92 parts for each 88 parts of butyric acid are made. The 

 author, however, believes that the additional corrections give 

 more exact results, though the difference due to neglecting them 

 is small. The whole system of corrections is based on a long 

 investigation made at the Government Laboratory, which has 

 established that, if milk is adulterated with added water, the 

 percentage added can be deduced from an analysis of the sour 

 milk, and that the figure thus obtained does not differ by more 

 than 3 per cent., and usually by much less from that estimated 

 by the analysis of the fresh milk. 



The author and Miller have submitted the Government Lab- 

 oratory method to a critical examination, and generally endorse 

 the above conclusions. 



Table XXXIX. gives the results of the analysis of 18 samples 

 of sour milk, corrected according to the foregoing scheme. 



Carbonic acid can only be estimated in koumiss or kephir 

 contained in a corked bottle. The worm of a champagne tap is 

 carefully turned off to leave a perfectly smooth stem ; the tap 

 is also carefully reground to make sure that it fits. 



A drying and absorbing apparatus is fitted up, consisting of 

 (a) a U-tube containing pumice and sulphuric acid, (b) a U-tube 

 containing soda lime immersed in a beaker of cold water, (c) a 

 U -tube filled half with soda lime and half with calcium chloride. 

 These are connected in the order named, and the end of (a) is 

 connected by a short piece of india-rubber tubing to the cham- 

 pagne tap. 



(6) and (c) are weighed, and the tap (closed) carefully forced 

 through the cork of the bottle ; the tap is opened slightly and 

 the carbon dioxide allowed slowly to escape ; when the escape of 

 gas becomes slack the bottle may be warmed slightly, by placing 

 it in warm water, and shaken to promote further escape. When 

 no more gas comes off the tap is disconnected, a soda lime 

 tube substituted, and a current of air drawn through the 

 apparatus. 



(6) and (c) are dried, cooled, and weighed again ; the increase 

 represents the amount of carbon dioxide which has escaped from 

 the bottle. The total contents of the bottle are now weighed 

 and the percentage is calculated. 



