THE ANALYSIS OF MILK 37 



the aldehyde figure (p. 38), are accurately measured 

 into a flask, which is placed so that the end of the 

 condenser dips into the liquid. Through the tube in the 

 cork 100 c.c. of a solution of caustic soda containing 

 300 grammes per litre are poured in, followed by 10 c.c. 

 of a 10 per cent, solution of sodium sulphide ; the tube 

 is closed, and the contents of the flask mixed by shaking ; 

 a flame is placed under the flask, and the ammonia 

 formed by the action of the sulphuric acid on the 

 proteins and liberated by the alkali, distilled over ; the 

 distillation takes about half an hour, a volume of ap- 

 proximately 200 c.c. being collected. A few drops of 

 cochineal are added to the distillate, and the excess of 



acid titrated with -- alkali (see Appendix). A blank 



experiment, i.e. one without the milk, should be per- 

 formed, and the difference between the volume of 

 alkali used in the blank and the experiment in cubic 

 centimetres multiplied by 0.0014 wm< gi ye the weight 

 of nitrogen ; this multiplied by 100 and divided by the 

 weight of the 5 c.c. taken will give the percentage of 

 nitrogen ; the nitrogen multiplied by 6.38 may be taken 

 as proteins in the milk. 



Estimation of Casein and Albumin Nitrogen. 

 To 10 c.c. of milk add 20 c.c. of a saturated solution 

 of magnesium sulphate, and crystals of the salt so long 

 as they are dissolved ; allow to stand for some time, and 

 filter off the precipitated casein, and wash this several 

 times with the saturated solution of magnesium sul- 

 phate (this is a slow process) ; place the filter and pre- 

 cipitate in a long-necked, hard glass flask, add 30 c.c. 

 of pure sulphuric acid and a drop of mercury, and pro- 

 ceed as above ; 150 c.c. of soda solution must be added 

 before distillation, and the distillate should be collected 



, N i 

 in 35 or 40 c.c. ot acid. 



The filtrate is diluted, and the albumin precipitated 

 by tannin ; the precipitate is collected on a filter, and 

 the nitrogen estimated as above. 



