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 moisture; 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 arin peas o proincing cold must be used in addition 
to ventilation, m en of above: ; but the ship started 
Ghethan wesc oe and not much time : 
: —— T suggested gees i ee ecetnat ele et — 
