86 Milk and Its Products 



and the surrounding circle painted in segments of 

 varying shades to represent cream, very rich milk, 

 normal milk, poor milk, etc. A drop of the milk 

 to be tested is placed in the central depression 

 and covered with a glass plate, so that a layer of 

 uniform thickness is always obtained. The opacity 

 of this drop of milk upon the black background 

 of rubber is then compared with a corresponding 

 segment of the circle. In so far as the fat 

 measures the opacity of the milk, this is a fairly 

 reliable test ; and, used in connection with a specific 

 gravity lactometer, a person with some experience 

 can readily detect suspected samples of milk, although, 

 of course, it is not possible to estimate very closely 

 the amount of adulteration or the quality of the 

 milk. The pioscope has been used very generally 

 and successfully by milk inspectors and those hav- 

 ing the control of city milk supply. 



Feser's lactoscope is another instrument designed 

 to determine the quality of milk by opacity. It 

 consists of a glass cylinder, in the center of which 

 is fixed a white rod graduated with black lines. 

 A certain amount of milk is put into the cylinder, 

 and by its opacity renders the black lines upon 

 the central standard invisible. Water is then added 

 to the milk in measured quantity until the black 

 lines can be seen, the amount of water so added 

 indicating the quality of the milk. This instru- 

 ment is more delicate than the pioscope, but it can 

 not be so quickly and readily used. The results 

 it gives are of very much the same nature and 



