38 DAIRY ANALYSIS 



The casein nitrogen and albumin nitrogen may be 

 multiplied by 6.38 to give the amounts of casein and 

 albumin respectively ; the sum of the two is usually a 

 little below the total nitrogen. 



Indirect Estimation from Organic Phosphorus 

 and Sulphur. Estimate the phosphoric acid in the ash 

 of the milk (see p. 15), preferably using 25 grammes 

 of milk ; evaporate 25 c.c. of the filtrate obtained by 

 adding Wiley's mercuric nitrate to milk for the polari- 

 metric estimation of milk sugar (see p. 30), ignite and 

 estimate the phosphoric acid in the ash of this ; multiply 

 the weight of P 2 5 by 4.42, and this will give the per- 

 centage of mineral phosphoric acid in the milk ; this 

 subtracted from the percentages of total phosphoric acid 

 will give the organic phosphoric acid, and the casein can 

 be calculated from this by multiplying by 50.8. 



Take 25 c.c. of milk, add 10 c.c. of strong nitric acid 

 and i gramme of sodium carbonate, evaporate to dryness, 

 and add 2 or 3 c.c. more nitric acid, and again evaporate ; 

 ignite to a fairly white ash, and take up the residue' 

 with dilute hydrochloric acid ; evaporate to dryness, 

 and boil the residue again with dilute hydrochloric 

 acid, and filter. Just raise the filtrate to boiling, and 

 add barium chloride solution drop by drop so long as a 

 precipitate is produced. Allow the solution to stand 

 24 hours to complete the precipitation, the first two 

 hours preferably in the water-oven, and collect the 

 precipitate on a small filter, wash well with hot water, 

 and place filter and precipitate still wet in a weighed 

 platinum dish ; ignite over a small flame till the paper 

 is burnt, and then more strongly ; the weight of the 

 precipitate (corrected for the ash of the filter) multiplied 

 by 13.7 and divided by the weight of milk taken will 

 give the percentage of sulphur in the milk. For each 

 71 parts of organic P 2 5 , 32 parts of sulphur belong to 

 the casein ; the remainder of the sulphur multiplied by 

 58.5 will give the albumin. 



Aldehyde Figure. This determination may be 

 combined with an acidity estimation; to 10 or n ex. 



