Intelligence and Miscellaneous Articles. 395 



In using carbonic acid snow to obtain intense cold it is usually 

 mixed with ether, as directed by Faraday and Thilorier. In these 

 conditions the ether is generally considered as intended to produce 

 a much more intimate contact with the body to be cooled than is 

 obtained with the snow alone. 



It is, however, a question whether ether has not a special action 

 other than that. 



We commenced by measuring the temperature obtained with 

 carbonic acid snow alone. A thermoelectric pincette, by which 

 a fraction of a degree could be estimated, was placed in the centre 

 of a large mass of this substance. In some cases the snow was 

 strongly compressed, and in others left to its ordinary porosity. 

 The results obtained varied very slightly, and the temperature of 

 the snow at the ordinary pressure is about — 60°. 



To try what effect a vacuum has on the temperature, we used a 

 Bianchi's rotatory air-pump and the absorbing action of potash ; 

 we were thus able to produce for some time together an almost 

 complete vacuum; but although the experiment was frequently 

 repeated, the conditions being varied as much as possible, the 

 temperature did not sink below — 76°. 



The same thermoelectric pincette gave us in the pasty mixture of 

 solid carbonic acid and ether a temperature of — 77° at the ordinary 

 pressure, and in a vacuum of about — 103°. 



The following experiment shows very neatly the special part 

 which ether plays. It is known that when a tube containing liquid 

 carbonic acid is immersed in the mixture, the contents of the tube 

 solidities very rapidly. If the temperature of the mixture were not 

 below that of the congelation of carbonic acid, this congelation 

 would not rake place. 



In order to ascertain the part played by the liquid in the mix- 

 ture we gradually added carbonic acid to ether. The first portions 

 of snow rapidly disappear in contact with the liquid. This dis- 

 appearance is not solely due to a volatilization resulting from the 

 difference of temperature, but to a solution of solid matter. For 

 the ether, which has kept its transparency and limpidity, disengages 

 carbonic acid steadily for a long time. By continuing the addition 

 of the carbonic acid snow, a point is reached at which it ceases to 

 dissolve, and the mixture then gradually becomes more and more 

 pasty. By following the changes of temperature with the thermo- 

 electric pincette, it will be observed that it sinks at each addition 

 of snow until the liquid, losing its transparency, indicates that it is 

 saturated. 



It appears then natural to admit that the cold produced by solu- 

 tion of solid carbonic acid in ether is the cause of the difference of 

 temperature observed between simple snow and the mixture. The 

 greatest cold is attained just at the point of saturation. 



It will be understood from this that if we vary the proportions 

 of the mixture the differences of temperature should be almost null, 

 provided there is an excess of solid snow which keeps up the satu- 

 ration. We have found in fact that, by varying the proportions 



