SKIM MILK. 253 



This sample contained an excess of cream, which made it 

 appear thick. 



Example b. — The sample gave a blue colour on adding iodine 

 solution. It was thickened with starch (or flour). 



Example c. — The milk was thick and, on dipping a glass rod 

 into it and lifting it out, a stringy mass adhered to it. On putting 

 the rod (which had been sterilised) into a bottle containing 

 sterilised milk, the latter acquired the same property in twenty- 

 four hours. The milk was " ropy." 



Problem VIII. — To determine the nature of sediment. 



In cases of this description, the milk should be placed in tubes 

 and centrifuged ; as much milk as possible must be decanted, 

 distilled water added, and the tubes again centrifuged ; this 

 procedure should be repeated till the water is clear. The sedi- 

 ment is examined microscopically (Fig. 31). 



^'egetable cells, if clear and sharply defined (Fig. 32), ari' 

 usually due to the bark of hay and the dust of cake given to thr 

 cnttle during feeding time. If indistinct and stained yellowish 

 or brownish, these usually indicate cow-dung (Fig. 33). 



Small hairs, cotton and woollen fibres usually show the pre- 

 sence of household dust. 



Crystalline particles usually indicate road dust. In this case 

 a little of the deposit is placed on a slide and warmed with dilute 

 hydrochloric acid, which is evaporated nearly ofi ; a drop of 

 water is added and also a drop of a solution of potassium ferro- 

 cyanide. A blue colour, due to iron, is obtained from road 

 dust. An estimation of the dirt may be made by aliowinu the 

 milk to stand, and measuring the amount in a graduated tube 

 (Fig. 34). 



Skim Milk. — The term " skim milk " is applied to milk from 

 which the bulk of the cream has been abstracted. Two ways of 

 abstract in;; the cream are practised : (1) by allowing the milk to 

 stand, taking advantage of the force of the earth's gravity to 

 separate the cream ; (2) by employing centrifugal force to attain 

 the same object. 



Distinction between Skimmed and Separated Milk. — 

 A distinction has been drawn between skim milk obtained by 

 these two methods ; that obtained by setting the milk being 

 called '■ skirrmied milk," and that obtained by centrifugal force 

 " separated milk." The distinction is one of degree, not of kind, 

 as, were it possible to keep milk without chemical change for an 

 indefinite period, the same result would ultimately be obtained 

 by either method. 



