194 MILK 



Dilution (with water or skimmed milk). — As shown 

 above, the density may have increased, decreased, or 

 undergone no change, depending upon the amount of 

 cream removed and the proportion of water added. 



The removal of cream will have led to a decrease 

 in the percentage of fat. Dilution with water would 

 not lead to any change in the proportion of fat in the 

 total solids, other than that accounted for by the 

 removal of cream ; dilution with skim milk would, how- 

 ever, show a further decrease in the percentage of fat 

 in the total solids. 



186. Preservatives. 



The addition of any preservatives whatever to milk is illegal. 

 The following tests for four of the commoner preservatives should 

 be carried out with four samples of milk, to which the following 

 preservatives have been added in the proportions given : — 

 No. I. 5 milligrams of boric acid per lo c.c. milk. 

 II. 5 drops of formalin per loo c.c. milk. 



III. 5 drops of hydrogen peroxide per loo c.c. milk. 



IV. .1 gram salicylic acid per loo c.c. milk. 



Detection of Boric Acid or Borates. — The first sample 

 of milk (lOO c.c.) is evaporated to dryness, and gently 

 ignited. The ash is then dissolved in a small quantity 

 of dilute HCl, filtered free from carbon particles, and 

 evaporated completely to dryness. 



(i.) A portion of the residue is dissolved in a little 

 very dilute HCl, and a piece of turmeric paper dipped 

 into the solution. The presence of boric acid is shown 

 by the fact that the paper will turn reddish brown on 

 drying in a steam oven, and this coloration can be 

 distinguished from that produced by the alkalies from 

 the fact that when moistened with a drop of an alkaline 

 solution, the brown colour is changed to greenish black. 



(ii.) A portion of the residue is placed in a test-tube 

 with a small quantity of concentrated HgSO^, a little 



