288 MILK AND THE PUBLIC HEALTH CHAP. 



The rate of cooling would be even slower if a larger bulk of 

 milk had been used. Milk (17 gallons) chilled to 4 to 6 C., 



FIG. 27. 

 Lawrence's Refrigerator. 



FIG. 28. 

 Cylindrical Refrigerator. 



kept at a room temperature of 19 to 21 C., took over 6 hours 

 to reach a temperature of 13 C. 



In another experiment a churn of milk, cooled to 6 '4 C., 

 was sent out in a milk cart at 11.40 A.M., covered with an 

 ordinary canvas churn cover to protect it from the direct rays 

 of the sun. It was driven about over parts of London, re- 

 turning to the depot at 4 P.M., when the mean temperature 

 of the milk was 10 '8 C. The initial air temperature was 

 18-6 C., and the final 21'6 C. (a warm summer day). In 



