I'.Y J. HROWNTJH: HENDERSON, F.I.(;., AN!> f.. A. MKSTON, 167 



of hundreds of thousands of analyses have added to the 

 certainty of the posit -ion. The freezing i:!oint of fresh milk 

 from a herd of cows seems never to vary further than from 

 —0-55° C. to -0-5G^ C. with a mean of -0-655° C. The 

 maximum variation represents about 2 per cent, of added 

 water, while the working error of the process is less than 

 0*5 ])er cent, of added water. 



Before dealing with the details of the method, it might 

 be well to note the reasons for the constancy of the freez- 

 ing point of a substance of such variable composition as 

 milk. 



The freezing point of a solution of a substance in water 

 depends mainly on the number of crj^stalloid ions dissolved 

 in the solution. 



Substances which are not in solution, like fat, do not 

 affect the freezing point. As fat is the most variable 

 component of milk, the most varying factor is removed 

 from affecting the result. Substances also which are in 

 " colloid " solution such as the albumenoids affect the 

 freezing point either not at all or only to a very slight extent, 

 and in any case as the molecular weight of the albumenoids 

 is very high, their relative effect on the freezing point is 

 very small. 



Thus the second most variable constituent of milk 

 does not appreciably affect the result. The milk sugar 

 content of milk is fairly regular, but again we are dealing 

 with a substance of high molecular weight and with a 

 correspondingly small effect on the freezing point. 



It will thus be evident that we get down to the small 

 proportion of other constituents ere we get the substances 

 which control the freezing point, and it seems that these, 

 as in the blood of nearly all animals, are almost perfectly 

 constant in proportion. 



The freezing point of milk is, therefore, not in any 

 degree whatever a measure of the proportion of Total Solids 

 or Solids not Fat present. 



We have found milks of known genuine origin from 

 small herds, with Solids not Fat 9-7 per cent, and 7-6 per 

 cent, as well as those of normal composition give exactly 

 — 0-555° C. freezing point. 



