1867.] Physics. 433 



Mr. H. Debray has communicated to the French Academy the 

 results of some experiments having for their object to demon- 

 strate that chemical decomposition is analogous to the evaporation 

 of a liquid, in the sense that the tension of the gas proceeding from 

 the decomposition is constant. He operated upon pure carbonate of 

 lime, Iceland spar, or ordinary impure carbonate of lime, placed in tho 

 middle of a tube, communicating sometimes with a mercurial pump 

 and sometimes with a gauge apparatus for measuring the tension of 

 the carbonic acid disengaged by the decomposition. The carbonate 

 was alternately submitted to four constant temperatures ; viz. 360° C. 

 (vapour of mercury), 440° (vapour of sulphur), 660° (vapour of 

 cadmium), 1040° (vapour of zinc). It was found that at 360° tho 

 tension of the vapour of the carbonic acid was absolutely nil; at 

 440° it was hardly sensible ; at 660° it was only 85 millimetres ; 

 at 104CP it attained 551 millimetres. 



A remarkable discovery has been made by M. Peligot, from 

 which it would almost seem as if the old tradition of the existence 

 of malleable glass was not quite so absurd after all. A piece of St. 

 Gobain glass, prepared a long time ago by M. Pelouze, had lost its 

 transparency owing to devitrification, but had not altered in density. 

 The piece of glass, supported by one extremity, was placed in a 

 drawer, when it was found, after some days, to have become curved 

 under its own weight, it having become in fact malleable glass ; the 

 surface at the same time being covered with efflorescence. Pliny 

 speaks in his history of a glass that could be bent and unbent ; and 

 the story goes that Bichelieu ordered an inventor to be put to death 

 for proposing to divulge a process for making malleable glass. 



The following very important conclusions have been arrived at 

 by Messrs. Bussy and Buignet in their memoir on the changes of 

 temperature produced by the mixture of liquids of different natures. 

 1. In all the cases under examination, with one sole exception, the 

 calorific capacity of the mixture is a little superior to the mean 

 capacity of the elements. 2. The liquids for which the increase of 

 bulk is the most considerable are exactly those which develop most 

 heat at the moment of their union, such as ether and chloroform, 

 alcohol and water, sulphuric acid and water. The only instance 

 hitherto noticed of a diminution of bulk is in the case of the mix- 

 ture of chloroform and bi-sutyhide of carbon, whilst at the same time 

 decrease of temperature takes place at the moment of the union. 

 3. Independently of the loss of heat resulting from the changes of 

 volume, there exists a cause which produces an absorption of heat, 

 which can be sometimes equal and even superior to the heat given 

 out by the combination of the liquids. This cause is not quite 

 clearly made out. It is suspected to be related to the phenomenon 

 of diffusion 



