896 Transactions. — Chemistry. 



In making freezing mixtures it is usual to dissolve in acid, but for this 

 purpose I think water would be best, as the solution might be evaporated 

 and recrystallized. In this way the salt may be used over and over again 

 any number of times. It may be mentioned that as a means of reducing 

 temperature on a considerable scale, it is impossible freezing mixtures could 

 be economized. But during a great part of the journey it would not be 

 difficult to prevent the temperature rising above 60° C, so that if not suit- 

 able for a long journey it may be a valuable adjunct. 



If expansion of air, evaporation, or night radiation, or any combination 

 of these processes, be used, then it is probable that it would be best to 

 exchange the air inside the chamber by the cooled air, although it is not 

 necessary to do so, as the cooled air may be passed along tubes with thin 

 copper bottoms thus acting in the same way as the freezing mixtures. 



In taking advantage of night radiation, a black bulb thermometer should 

 be consulted, and when it stands low air should be passed through a vessel 

 with a thin copper top, the other parts being nonconducting; the copper 

 should be smoked on each side. Arrangements would, of course, have to 

 be made to catch the water precipitated. The air by its own density would 

 pass down its tube to the bottom of the chamber, and it may not be neces- 

 sary to use any artificial means of propelling the air. 



If air expansion be used, then the strong vessel into which the air is 

 compressed having been allowed to cool, the air must be allowed to expand 

 into a separate vessel to precipitate moistm*e ; this may be either a non- 

 conductor outside the chamber, or a conductor placed inside ; the latter 

 would probably be the most economical. 



Evaporation should be taken advantage of .when the wet bulb thermo- 

 meter is much lower than the dry bulb. Of course a Daniel's Hygrometer 

 would be a superior test ; the cooling may take place in copper tubes 

 covered with calico, kept wet by water dripping on it. This method may 

 be used with any of the others already mentioned. The whole of the 

 methods are so extremely simple that any intelligent man would quickly 

 know how to use any one or any combination. 



I was told that it was mentioned in a paper that the recent cheese and 

 butter shipment was made under my instructions ; but my connection with 

 the experiment was a very simple one. It was proposed to keep the chamber 

 cool by passing ordinary air through it. I explained that this could not 

 possibly reduce the temperature below that of the air of the tropics, and 

 suggested that artificial means of producing cold must be used in addition 

 to ventilation, mentioning the methods spoken of above ; but the shijj started 

 in a few days, so there was no time to make machinery, and not much time 

 for experiment, I suggested that if the experiment must be thus hurried, 



