THE ANALYSIS OF MILK. 87 



such a nature as to permit of its practical application in milk-testing. 

 Nor would this test be very valuable in view of the many adulterations 

 which it would fail to detect. 



The proof of the addition of carbonates or alkali bicarbonates is most 

 easily obtained by incinerating 300 to 500 grams of milk, and determining 

 the percentage of carbonic acid in the ash. The ash of unadulterated milk 

 does not contain more than 2 per cent of carbonic acid; while anhydrous 

 carbonate of soda contains 41*5 per cent. If the percentage of carbonic 

 acid in milk exceeds 2 per cent, this may be regarded as a certain indi- 

 cation that an alkaline carbonate has been added to the milk. Even an 

 addition of 1'5 grams of anhydrous soda to a litre of milk imparts to it a 

 distinct soapy taste. In Hilger's process 50 c.c. of the milk are diluted 

 with five times the quantity of water, coagulated with a small quantity 

 of alcohol, and filtered. If the filtrate be evaporated to half its bulk, an 

 alkaline reaction indicates the presence of an alkaline carbonate. 



The presence of salicylic acid in milk is best detected by Pellet's 

 method. 100 c.c. of the milk to be investigated, 100 c.c. of water at 60 C., 

 five drops of acetic acid, and five drops of a solution of mercury oxide in 

 nitric acid are mixed together, shaken, and after the albumin has been 

 coagulated the mass is filtered. The clear filtrate is then shaken with 

 50 c.c. of ether. After the ether has separated out it is removed, placed 

 in a clean vessel, diluted, the residue dissolved in a few drops of water, 

 and tested to see if it will give, on the addition of two drops of a 1 -per- 

 cent solution of iron perchloride, a violet coloration. If it shows a 

 coloration, its amount can be determined by comparing the depth of 

 colour produced with a standard solution of salicylic acid and iron per- 

 chloride. The amount of salicylic acid can in this way be approximately 

 determined. 



In order to test the quantity of boracic acid in milk, Meissl recommends 

 the following process: 100 c.c. of milk are rendered alkaline with milk 

 of lime, evaporated, and incinerated. The ash is dissolved in the least 

 possible amount of concentrated hydrochloric acid, the carbon is filtered 

 off, and the filtrate is evaporated to dryness, the hydrochloric acid being 

 in this way completely driven off. A small quantity of a very dilute 

 solution of hydrochloric acid is then used to damp the ash. The crystal- 

 line mass is then treated with kirkuma (a tincture of turmeric, prepared 

 according to Fresenius, Qualitative Analysis, 14th Edition, p. 90) and dried 

 in the water-bath. In the presence of even very small quantities of boracic 

 acid the dry substance exhibits a colour from cinnabar to a cherry-red. 

 The reaction is so delicate that even -001 to '002 per cent of boracic acid 

 can be easily detected in milk. An exact quantitative determination of 

 boracic acid in milk is not possible. The amount present can, however, be 



