282 PETER SPENCE 



at Exeter, in August, 1862. He desired 

 to obtain a temperature 228 Fahr., to 

 extract alumina in the form of sulphate from 

 minerals containing that earth. His 

 apparatus was heated by steam and fire, and 

 he was able to digest for a long period the 

 solutions at the necessary temperature. It 

 happened that, by accident, the fire was 

 neglected and the steam alone operated; 

 nevertheless, to his surprise, he observed the 

 high temperature was preserved; he was led 

 to investigate, and experiment on this pheno- 

 menon ; he selected a solution of a salt (nitrate 

 of soda) having a high boiling point about 

 250 Fahr. The nitrate of soda was placed 

 in a vessel surrounded by a jacket; steam at 

 atmospheric pressure was let into the inter- 

 vening space, until a temperature of nearly 

 2i2 Q Fahr. was obtained; the steam was then 

 shut off, and an open pipe immersed in the 

 solution, and the steam from the same source 

 was thrown directly through it into the liquor; 

 in a few seconds the thermometer slowly, but 

 steadily moved, and minute after minute 

 progressed until it touched 250** Fahr. 



This thoroughly confirmed the results 

 obtained in the digesting vessel and became 

 to the author of great practical value. 



