PA S TE URIZA TION. 



181 



would have the same resistance to heat as a layer of copper 

 2 meters in thickness. Consequently a very thin layer of water 

 or condensed steam on the sides of the heating-wall would 

 greatly interfere with the economic efficiency of a pasteurizer. 



In order to overcome this difficulty drip-rings were circled 

 round the drum of the pasteurizer at intervals on the steam side 

 of the heating-surface . The first rings put around the pasteurizer 

 were narrow smooth bands. These did not give entire satisfac- 

 tion, as the condensed water from the top rings would drip on 

 the edge of the lower ones, and cause the water to splatter over 

 the side of the heating- wall. Another kind of ring was then in- 

 vented, which 

 was thin, nar- 

 row, and saw- 

 teeth-like in 

 shape. These 

 rings were fast- 

 ened to the 

 heating-wall at 

 proper inter- 

 ■s'als at an angle 

 of 45° The 

 rings were so 

 arranged that 



the drops of condensed water escaping from the end of each saw 

 tooth would fall in the hollow between the teeth in the lower rings 

 and thus prevent any splattering of the ^^'ater against the heating- 

 wall. These contrivances greatly increased the efficienc}' — as high 

 as 48% — and the capacity of the pasteurizer experimented upon. 



(4) Difference in Temperature on Each Side of the Heating- 

 surface. — The difference in the temperature on each side of the 

 heating-surface has a great elfect upon the rapiditj' with which 

 the heat passes through the wall. The lower the temperature 

 is on the milk side the more rapidly does the heat pass through ; 

 and the higher the temperature of the milk is, the pressure on 

 the steam side being the same, the more slowly the heat passes 

 through the heating-wall. This would at first lead us to be- 



The Farrington pasteurizer. 



