140 ANALYSIS OF MILK. 



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 

 dif5:erence. 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 

 large volume of alkali required for neutralisation. 



For the estimation of the specific 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 from 

 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 to operate 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 

 the lowering of the specific gravity of the fresh milk, the correc- 

 tion to be made for the ammonia is deduced ; this is usually 

 0-0026 or 0-0027, or 2-6 to 2-7 lactometer degrees. 



de Koningh proposes the use of a solution of caustic soda of 

 specific gravity r030 instead of the ammonia; he finds that 

 on mixing 5 c.c. of this solution to 100 c.c. of piilk that a lowering 

 of the specific gravity by 0-0008 or 0-8 degree takes place. The 

 author and Harrison find that with fresh milks the lowering is 

 less, 0-0003 on the average, and increases with the acidity of the 

 milk ; the cause of this lowering is shown by their experiments 

 to be due to the fact that the specific gravity of a solution of a 

 sodium salt is always less than the sum of the specific gravities 

 of equivalent solutions of caustic soda and an acid (less 1). The 

 following procedure has given good results in the author's hands : 

 — Add sufficient solution of caustic soda (sp. gr. 1-032) to render 

 the mixture with the sour milk distinctly alkaline to phenol- 

 phthalein ; determine the specific gravity of the mixture and 

 the acidity of the sour milk (see p. 133). To the figure found 

 for the specific gravity add the acidity in degrees multiplied by 

 0-000022, and subtract O'OOOl ; thus, if the specific gravity 

 found be r0305, and the acidity be 70°, the corrected specific 

 gravity is 



1-0305 + 70 X 0-000022 - 0-0001 = 1-0305 -1- 0-00154 - 0-0001 = 1-0319. 

 Estimalion of Proteins. — The proteins precipitated by the acid 



