62 DAIRY ANALYSIS 



of course, distinguish between added cane sugar or added 

 milk sugar, but when it is known what the added 

 substance is, an estimation of sufficient accuracy is 

 obtained. 



Detection of Adulteration of Cream. As there 

 is no standard for cream, it may contain any per- 

 centage of fat, and still be cream ; there is a practical 

 standard of " thickness " which the purchaser mentally 

 estimates, and judges the value of the cream thereby. 

 Artificial thickening is sometimes resorted to, and 

 gelatinised starch, gelatine, " viscogen " (a solution of 

 lime in cane-sugar syrup), condensed milk or milk 

 powder, and collagens are added. 



Starch is detected by the blue colour produced on 

 adding a solution of iodine in potassium iodide. 



Gelatine is found, if present, by diluting the cream 

 with water and adding a little acid mercuric nitrate solu- 

 tion (see Appendix) ; the filtrate, if gelatine is present, 

 is usually turbid, and gives a precipitate on the addition 

 of a saturated solution of picric acid. 



Viscogen raises the percentage of lime in the ash ; 

 the lime on an average amounts to 22 per cent, of the 

 ash, and its ratio to phosphoric acid (CaO to P 2 5 ) is 

 i : 1.3. Viscogen raises not only the percentage in 

 the ash, but also the ratio to the solids not fat. A 

 small cane-sugar reaction may be obtained, and the 

 percentage of sugar polarised as milk sugar will exceed 

 52.5 per cent, of the solids not fat. 



Condensed milk or milk powder may be detected by 

 the solids not fat being found in much greater propor- 

 tion than that given as corresponding to the fat found 

 in Table V ; the percentages of ash, milk sugar, and 

 proteins, and the aldehyde figure will bear the same 

 proportion to the solids not fat as found in milk. Clotted 

 or Devonshire cream, however, is concentrated during 

 its preparation, but its physical appearance differs from 

 that of raw cream, and it does not give the reactions 

 with hydrogen peroxide given on p. 54. 



Collagens are difficult of detection ; they raise the 



