190 THE ANALYSIS OF MILK PRODUCTS. 



Skim Milk. The methods of milk analysis may be applied ; 

 the fat is rather more difficult of extraction. If Ritthausen's 

 method be used for protein determination, it is not necessary to 

 extract the fat, but to dry and weigh the copper precipitate, and 

 afterwards to subtract the percentage of fat found from the 

 percentage of proteins plus fat. 



Condensed Milk. About 30 to 35 grammes of the well- 

 mixed milk should be weighed into a 100 c.c. flask, diluted with 

 50 to 60 c.c. of water, and the solution raised to the boiling 

 point ; this is cooled, made up to 100 c.c., and the total weight 

 taken. The diluted solution is analysed as milk. The fat is 

 rather more difficult to extract by Adams method than from 

 ordinary milk, and longer extraction should be given ; the 

 Gottlieb method is the best ; if cane sugar is present, the Werner- 

 Schmid process must not be used for the estimation of the fat, 

 as cane sugar yields a substance soluble in ether. The Ritthausen 

 method must not be used. When soluble albumin is estimated, 

 a fresh portion which has not been boiled is employed. 



Sour, Fermented, or Decomposed Milk. Preparation of 

 Sample. The whole contents of the bottle are turned out into 

 a beaker and whisked for a minute or two with a brush made of 

 fine wire ; the inside of the bottle is scraped all over with a wire, 

 some of the milk is poured back, and the contents shaken ; this 

 is now emptied into the beaker and again whisked. 



Many samples on mixing yield a portion of their fat in a churned 

 condition, which adheres to the wire brush ; in these cases a 

 separate estimation of the churned fat should be made. 



The estimation of fat in sour milks has already been discussed 

 under the various methods ; milk-sugar and cane sugar, if present, 

 are almost impossible to estimate, as they have usually undergone 

 more or less hydrolysis, and are usually neglected or estimated by 

 difference. Total acidity and aldehyde figure are estimated as 

 described ; it is, however, necessary to add a larger quantity 

 of formaldehyde solution on account of the great dilution by the 

 arge volume of alkali required for neutralisation. 



For the estimation of the s-pecific gravity of curdled milk 

 Weibull recommends the addition of ammonia, which dissolves 

 the precipitated curd ; the specific gravity of the mixture is 

 taken, and the specific gravity of the milk is calculated frorr 

 that of the mixture, and that of the ammonia. The method 

 gives excellent results, but, as the estimation of the specific 

 gravity of ammonia is an unpleasant operation, the author 

 prefers operating as follows : To 100 c.c. of curdled milk add 

 5 c.c. of dilute ammonia (1 part ammonia, sp. gr. 0-885, to 4 parts 

 of water), mix well, and take the specific gravity ; to 100 c.c. 

 of fresh milk add 5 c.c. of the same ammonia solution, and from 



