8o MILK AND DAIRY PRODUCTS PART 



6. Gerber s "Sal" Method. 



Following the principle of the Sinacid method, Gerber 3 has 

 worked out a modification of his original test, which is known 

 as the " Sal " method. In this method a mixture of sodium 

 hydrate, Rochelle salt, and sodium chloride is used to dissolve 

 the casein, and instead of amyl alcohol the pleasanter isobutyl 

 alcohol is employed. The test is made in the usual Gerber 

 apparatus, and gives results which are quite as good as those 

 got in the acid method. 



When using the Sal method, the butyrometer tube must be 

 filled in the following order : 



11 c.c. of Sal solution, 

 O6 butyl (isobutyl alcohol), 

 10 well-mixed milk, 



and the temperature should be about 15 C. 



The rubber stoppers used in the tubes should fit well and be 

 dry, and screwed in so that the liquid reaches to the upper 

 third of the scale. Great care should be exercised in mixing 

 the contents of the tubes, the liquid, after each shaking, being 

 allowed to flow down again into the graduated portion. Then 

 the tubes are put into a water-bath at about 45 C., allowed to 

 stay there three minutes and again shaken for a short time, and 

 finally put in the centrifuge. 



The centrifuge should be whirled for 2-3 minutes at a rate 

 of 800-1,000 revolutions per minute, and when the tubes are 

 taken out they should be warmed again to 45 C. and read off. 

 With skimmed, separated, or other milk poor in fat, the reading 

 is taken from the middle of the meniscus, and not from the 

 lower surface as in whole milk. ' 



IV. DETERMINATION OF THE NITROGENOUS SUBSTANCES. 



1. Estimation of the Total Protein, 

 (a] Determination of the Total Nitrogen. 



By determining the amount of nitrogen in milk by Kjeldahl's 

 method, and multiplying the result by 6'37, the quantity of 



1 Milch- Zeitung, 1906, No. 4. 



