THE TESTING OF MILK AND CREAM 



145 



4 I 



which is attached to the bottom of the tester. A handy type 

 of tester is shown in Fig. 38. The amount of dirt that col- 

 lects on the disk shows the amount of dirt contained in that 

 pint of milk. The disk is readily replaced by a new one and 

 thus many samples of milk can be successively 

 tested. The rapidity with which the milk is filtered 

 through the cotton is quite important where a large 

 number of samples are to be tested ; this filtration 



may be hastened by apply- 

 ing either heat or pressure 

 to the milk. One type of 

 these testers is provided 

 with a steam jacket for 

 heating the milk; and an- 

 other, with a tightly closed 



FIG. 38. A convenient milk cover and a rubber pres- 

 sure bulb by means of 



which the milk is forced through the filter. No heat 

 is necessary with the latter. After one sample of 

 milk has passed through the filter this is removed 

 and placed on a small card or piece of white paper. 

 A new cotton disk is then placed on the wire gauze of the 

 apparatus and another sample tested. 

 Test for the detection of formaldehyde. 



Five c.c. of milk are measured into a white porcelain dish, and 

 a similar quantity of water added ; 10 c.c. of hydrochloric acid 

 (HC1), containing a trace of tetrachloride of iron (FejCle), is 

 added, and the mixture is heated very slowly. If formaldehyde 

 is present, a violet color will be formed. (Testing Milk and 

 Its Products, Farrington and Woll, p. 249.) 

 Test for boracic acid (borax, borates, preservaline, etc.). 



One hundred c.c. of milk are made alkaline with a soda or 

 potash solution, and then evaporated to dryness and incinerated. 

 The ash is dissolved in water, to which a little hydrochloric 



