QUANTITATIVE ANALYSIS OF MILK. 411 



(b) Approximate Determination by Feser's Lactoscope. Milk 

 is opaque mainly because of the suspended fat globules and there- 

 fore by means of the estimation of this opacity we may obtain data 

 as to the approximate content of fat. Feser's lacto- 

 scope (Fig. 126, p. 411) may be used for this purpose. 



Proceed as follows : By means of the graduated pip- 

 ette accompanying the instrument introduce 4 c.c. 

 of milk into the lactoscope. Add water gradually, 

 shaking after each addition, and note the point at 

 which the black lines upon the inner white glass cylin- 

 der are distinctly visible. Observe the point on the 

 graduated scale of the lactoscope which is level with 

 the surface of the diluted milk. This reading repre- 

 sents the percentage of fat present in the undiluted 

 milk. Pure milk should contain at least 3 per cent 

 of fat. 



3. Total Solids. 1 Introduce 2-5 grams of milk FESER ' S 

 into a weighed flat-bottomed platinum dish 2 and LACTOSCOPE. 

 quickly ascertain the weight to milligrams. Expel the 



major portion of the water by heating the open dish on a water-bath 

 and continue the heating in an air-bath or water oven at 97-ioo 

 C. until the weight is constant. (If platinum dishes are employed 

 this residue may be used in the determination of ash according to 

 the method described below.) 



Calculation. Divide the weight of the residue, in grams, by the 

 weight of milk used, in grams. The quotient is the percentage of 

 solids contained in the milk examined. 



4. Ash. Heat the dry solids from 25 grams of milk, obtained 

 according to the method just given, over a very low flame 3 until 

 a white or light gray ash is obtained. Cool the dish in a desiccator 

 and weigh. (This ash may be used in testing for preservatives ac- 

 cording to directions on page 226.) 



1 The percentage of total solids may be calculated from the specific gravity and 

 percentage of fat by means of the following formula which has been proposed 

 by Richmond: 



8 = 0.25 L + 1.2 F + o.i4 

 S =. total solids. 

 L = lactometer reading. 

 F = fat content. 



~ Lead foil dishes, costing only about one dollar per gross, make a very 

 satisfactory substitute for the platinum dishes. 



3 Great care should be used in this ignition, the dish at no time being heated 

 above a faint redness, as chlorides may volatilize. 



