PHYSICAL AND CHEMICAL EXAMINATION OF MILK 175 



The following table shows the results of Babcock tests of skim- 

 med milk compared with those obtained by gravimetric analyses 

 (Beach) : 



ANALYSES OF SKIMMED MILK BY THE BABCOCK METHOD, USING 17.6 AND 25 C.C. ACID, 

 COMPARED WITH ANALYSES BY GRAVIMETRIC METHOD 



Gravimetric Per cent, fat, steam turbine tests. 



Sample No. method. 17.6 c.c. acid. 25 c.c. acid. 



1 0.141 0.045 0.060 



2 0.143 0.055 0.055 



3 0.149 0.015 0.030 



4 0.122 0.025 0.055 



5 0.121 0.080 0.080 



6 0.118 0.060 0.090 



7 0.147 0.055 0.085 



8 0.213 0.065 0.090 



9 0.135 0.020 0.035 

 10 0.158 0.040 0.050 



The Babcock readings were always lower than gravimetric 

 analyses, although the steam turbine kept the fat at a high tem- 

 perature and the bottles were whirled for six minutes at full speed. 



THE DETERMINATION OF TOTAL SOLIDS AND PLASMA SOLIDS 



Total solids are determined by weighing 2 to 5 grams of milk 

 in an evaporating dish, preferably a platinum dish, and evaporating 

 the contents to dryness. Porcelain dishes, glass dishes, or those 

 made of aluminum, nickel, or tin may be used, but a platinum 

 dish is most suitable, especially when the ash is to be determined. 

 The dish containing the milk is placed on a water-bath. After 

 the water has been driven off, the outside of the dish is wiped and 

 the dish placed in a desiccator to remove the last traces of moist- 

 ure. By weighing the solids the percentage is finally calculated. 

 A small amount of sand may be added to the milk before evapora- 

 tion is begun. 



Evaporation of milk for the determination of total solids is 

 frequently carried on in specially constructed ovens. These ovens, 

 of which several styles are used, are so constructed as to have a 

 steam jacket surrounding the inner part of the oven. The tem- 

 perature, therefore, is not above 100 C. Higher temperatures 

 cause decomposition of some of the constituents and must be 

 avoided. 



Two methods for determining total solids are given by the 

 Association of Official Agricultural Chemists, as follows : 



"Method 1. Heat from 3 to 5 grams of milk at the temperature 

 of boiling water until it ceases to lose weight, using a tared flat 

 dish of not less than 5 cm. diameter. If desired, from 15 to 20 

 grams pure dry sand may be previously placed in the dish. Cool 

 in a desiccator and weigh rapidly to avoid absorption of hygro- 

 scopic moisture. 



