344 



PHYSIOLOGICAL CHEMISTRY 



(d) N ephelometric Method of Bloor. 1 This method is exactly similar in principle 

 and procedure to the method given for the determination of fat in blood. (See 

 page 300.) One c.c. of milk is ordinarily taken. 



(e) Approximate Determination by Peter'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 con- 

 tent of fat. Feser's lactoscope (Fig. 114) may 

 be used for this purpose. Proceed as follows: 

 By means of the graduated pipette accompany- 

 N ing 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 

 cylinder 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 represents the percentage of fat present 

 in the undiluted milk. Pure 

 milk should contain at least 3 

 per cent of fat. 



4. Total Solids. 2 Intro- 

 duce 2-5 grams of milk into a 

 weighed flat-bottomed plati- 

 num dish 3 and quickly ascer- 

 tain 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-iooC. until th,e weight 

 is constant. (If platinum 

 dishes are employed this 

 residue may be used hi the 



determination of ash according to the method described below.) 



Calculation. 4 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. 



ID r 



FIG. 113. SOXHLET APPARATUS. 



>II4< _ FESER , S 

 LACTOSCOPE. 



1 Bloor: /. Am. Chem. Soc., 36, 1300, 1914. 



4 ShackelPs method for the vacuum desiccation of frozen preparations may be used 

 where great accuracy is desired (see American Journal of Physiology, 24, 325, 1909). 



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

 substitute for the platinum dishes. 



4 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+i. 2 F+o.14 

 S = total solids. 

 L= lactometer reading. 

 F=fat content. 



