STANDARDS. 



357 



cent, of ash may be adopted for the purpose of judging whether 

 a milk is of genuine composition or not. The figure for the 

 ash is, however, liable to be increased by the addition of mineral 

 substances to the milk ; thus boric acid and borax, used 

 as preservatives, and salt, added to mask the addition of water, 

 would raise the ash ; estimation of the boric acid, which is 

 absent in genuine milk, or of the chlorine, which does not often 

 exceed 0-10 per cent., will show additions of this nature. The 

 amount of ash insoluble in hot water is also a useful figure ; 

 it amounts in milk to at least 0-50 per cent., and is very nearly 

 equal to the total nitrogen. 



A milk never should be pronounced as watered on the evidence 

 of the solids not fat alone, unless this is well below 8-0 per cent.-; 

 a determination of the milk-sugar, total nitrogen, and ash should 

 be made in addition ; a judgment formed on the three determina- 

 tions will be in all probability correct, and if the figures for at 

 least two of them are above the limit, the milk is probably 

 genuine. 



Variations of Fat in Milk on Standing. The fat 

 globules of milk have a natural tendency to rise to the surface 

 and to cause thus an unequal distribution of fat in different 

 portions of the milk. 



Table CXXV. will give an idea of the rate at which appreci- 

 able change in the composition of the milk occurs ; 12 gallons of 

 well-mixed milk were placed in a churn with a tap at the bottom 

 at 11.25 a.m., and a measure holding 7 quarts was drawn out 

 every half -hour till 2.25 p.m. ; each of these quantities was 

 analysed, as also the residue left in the churn (5 quarts) ; the 

 milk was undisturbed throughout. 



TABLE CXXV. VARIATIONS IN COMPOSITION OF MILK ON 

 STANDING (LARGE CHURN). 



In another experiment two small churns, such as are used in 

 restaurants, each holding 12 quarts, were stood side by side ; 



