1882.] SETTING MILK. 303 



Taking these results and those of the first series, together with 

 the observations hitherto made, it may be regarded as most prob- 

 able that with deep setting, using the quantity of ice employed in 

 these trials, it does not pay to let milk stand more than twenty- 

 four hours, and if a larger amount of ice is required it may not 

 pay to let it stand more than twelve even; while if the Holstein 

 method is followed it will pay to let the cream rise, for thirty-six 

 hours. 



We see that in the first twelve hours more fat separated by the 

 Swartz method than by the other ; a fact which is all the more 

 striking if we consider that the fat globules had to rise seven or 

 eight times as far in the first case as in the second. Such observa- 

 tions as these, repeatedly made, have raised the much vexed ques- 

 tion, ""What temperature is best for raising cream ? " But such a 

 question is not quite fairly put. In neither method does the milk 

 for the whole twelve hours keep the same temperature. From 

 the time milk is set in ice water its temperature changes from mi- 

 nute to minute sinking without interruption till at last it reaches 

 about the temperature of the surrounding water, and from then 

 on is nearly stationary. The question would be better put thus : 

 Does rapid or slow cooling give the larger yield of fat within a 

 reasonable time ? 



To the first question, what constant temperature — that is, un- 

 changing from the time of setting to the time of skimming — is 

 most favorable, the author on theoretical grounds, supported too 

 by observation, would answer — a higher temperature than obtains 

 in Swartz's system. The milk serum becomes more and more dense 

 as the temperature sinks and offers increased resistance to the rise 

 of the butter globules. 



But to the other question — Which method of cooling, slow or 

 rapid, will give the larger yield of fat within a reasonable time — 

 he would answer, rapid cooling is preferable. The more quickly 

 the milk cools from the sides and bottom of the vessel in which it 

 stands, and in consequence of this the more promptly the perpen- 

 dicular currents through the milk to and from the surface are 

 checked, the sooner can the butter globules move freely and without 

 interruption to the surface. At the same time it must be borne in 

 mind that the cooling should not go below a certain point, for as 

 it approaches 32° the serum becomes thicker and the subsequent 

 rise of the butter globules is very slow. 



In accord with this view is the observation that by the Hoi- 



