26 MILK ANALYSIS 



Cows^ Milk. — The determination should be made when the 

 milk is fresh. When it is not practicable to make the deter- 

 mination within 24 hours, add one part of formaldehyde to 

 2500 parts of milk and keep in a cool place. 10 grams of the 

 sample are diluted with about 90 c.c. of water at between 40° 

 and 42", 1.5 c.c. of a solution containing 10 per cent, of acetic 

 acid by weight added, allowed to stand for five minutes, 

 washed three times by decantation, pouring the washings 

 through a filter, and the precipitate transferred completely to 

 the filter. If the filtrate is not clear at first, it will generally 

 become so in two or three filtrations, after which the washing 

 can be completed. The nitrogen in the washed precipitate 

 and filter is determined by the Kjeldahl- Gunning method. 

 The nitrogen, multiplied by 6.38, gives the casein. 



In working with milk which has been kept with preservatives, 

 the acetic acid should be added in small portions, a few drops 

 at a time with stirring, and the addition continued until the 

 liquid above the precipitate becomes clear or nearly so. 



2. Provisional Method lor the Determination of Albumin in 

 Milk. — The filtrate obtained in the above operation is neutral- 

 ized with sodium hydroxid, 0.3 c.c. of the 10 per cent, solution of 

 acetic acid added, and the mixture heated for 15 minutes. 

 The precipitate is collected on a filter, washed, and the nitro- 

 gen determined. 



The following method has been found satisfactory, avoiding 

 the difficulty of washing the precipitate: 10 c.c. of the milk 

 are mixed with saturated magnesium sulfate solution and the 

 powdered salt added to saturation. The mixture is washed 

 into a graduated measure with a small amount of the saturated 

 solution, made up to 100 c.c. with the same solution, mixed, 

 and allowed to stand until the separation takes place. As 

 much as possible of the clear portion is drawn off with a pipet 

 and passed through a dry 'filter. An aliquot portion of the 

 filtrate is taken, the albumin precipitated by a solution of 



