THE ADULTERATION OF MILK. 



531 



Specific gravity 1 03 



Total solids 12 50 



Fat ; 3-20 



Organic solids not fat 870 



Mineral salts '60 



Water 87-50 



The sample of milk selected for examination should be quite fresh, but 

 never warm. The temperature should be about G0° F. 



Of the several determinations required, that of specific gravity is 

 at once the easiest and the most important. It is made either by 

 means of the specific-gravity bottle or the hydrometer. 



The specific-gravity bottle is a small glass flask which will contain 

 a given weight of distilled water. The form used by the writer is 

 shown in Fig. 1. It is adjusted to fifty grammes of water, and is ac- 

 companied by a small brass weight to 

 exactly counterpoise the weight of the 

 flask. To determine the specific gravity 

 of a sample of milk the bottle is com- 

 pletely filled with the milk and the stop- 

 per brought into contact with the fluid, 

 care being taken that no air adheres to 

 its under side. The stopper is then per- 

 mitted to fall quickly into its bearing 

 in the neck of the bottle. The excess 

 of milk escapes through the fine perfora- 

 tion in the stopper. In this way an 

 invariable volume of fluid is always 

 weighed. The flask is then carefully 

 wiped off, and the whole weighed, re- 

 membering, of course, to add the coun- 

 terpoise weight to the scale-pan, in or- 

 der to allow for the weight of the flask. 

 The weight of the milk is obtained in 

 grammes, and this multiplied by "02 will 

 give its specific gravity directly. 



By the use of the hydrometer (or lactometer, as it is usually called, 

 when graduated for milk), the determination of the specific gravity 

 may be made much more rapidly. A convenient form of this instru- 

 ment is shown in Fig. 2. It will require no explanation beyond brief 

 mention of the system of marking employed. The upper graduation 

 on the stem of the tube is marked 1, and is the point to which the in- 

 strument will sink when placed in pure, distilled water, at 60° F. The 

 lower graduation is marked 1-05, and is the point to which the instru- 

 ment will sink when placed in a fluid of that specific gravity. As 

 normal milk averages 1'03, the variations on either side will be fully 

 covered by these limits. A low specific gravity indicates that the 



Fig. 1.- 



-Fifty-Gramme Sfecific- 

 Gbavity Bottle. 



