188 MASS. EXPERIMENT STATION BULLETIN 187. 



An attempt to add dirt to certified milk and recover or determine it 

 after passing the clarifier was undertaken by the method of differences. 

 This, however, is subject to the error in clarifying the same sample of milk 

 in two lots; the possibility of such error can be ascertained by consulting 

 page 160. Even though the same conditions are observed throughout as 

 considered previously, except the addition of dirt, the error resulting in 

 clarification is real, and the method of differences here used cannot be 

 accepted as absolute. So difficult is it to extract dirt from slime and weigh 

 it that the results must be considered as indicative only. 



If, for instance, an addition of a solvent to the slime for releasing the 

 dirt is made, the solution of the dirt is increased. When 1 per cent, of 

 KOH is added to dry manure the per cent, of solution goes to 28.5, 32.5 

 and 32, instead of 24 and 24.5, as in the case of water. 



To illustrate the results obtained by the addition of about .2000 to 

 .5000 gram of dirt to one liter of milk, the following determinations are 

 given: — 



Table XVIII. — Solvbilihj of Dirt in Milk. 



No. 1. 1 Grams. 



Slime from 1 liter of normal milk, . . . . . . . . . 2 . 2504 



Slime from 1 liter of normal milk + .5000 gram dirt 2.9123 



Difference representing dirt recovered, ......... .6619 



No. 2. 



Slime from 1 liter of normal milk, . . . . . . . . . 1 . 1276 



Slime from 1 liter of normal milk + .5044 gram dirt, . . . . . . 1.5519 



Difference representing dirt recovered, ......... .4243 



No. 3. 



Slime from 1 liter of normal milk, ......... 1.7432 



Slime from 1 liter of normal milk + .2000 gram dirt, 1.9340 



Difference representing dirt recovered, ......... .1908 



1 In this case the difference represents more dirt than was added. 



In the above samples the certified milk or normal milk represented the 

 minimum amount of dirt present in milk; accordingly, it doubtless had 

 little effect on the results obtained. While it is unjustifiable to say that 

 the amounts recovered from the slime, after the milk has had added a 

 definite amount of dirt and has been through a clarifier, indicate the effi- 

 ciency of the clarifier in removal of dirt, it is justifiable to infer that a 

 portion of the insoluble part is removed. A lack of exact methods, as 

 heretofore hinted, by which dirt is separated from the remainder of the 

 slime precludes drawing more definite conclusions or giving more satis- 

 factory data. 



The removal of dirt has been approached from another angle, which will 

 help in understanding the nature of dirt in milk in its relation to clarifica- 

 tion. In one instance 5 pints of commercial milk were passed through 

 the Wisconsin Sediment Tester, using individual discs of cotton for each 

 pint. The milk was then allowed to pass directly into the clarifier receiv- 

 ing can and clarified immediately. The slime eliminated by the clarifica- 

 tion was tested by macerating the slime and centrifuging. Visible amounts 



