PROGRESS IN PHYSICAL CHEMISTRY. 309 



such as silver, mercury, platinum, etc., to the prolonged 

 action of high pressure amounting at most to 1,000,000 lbs. 

 per square inch, a certain small amount of decomposition 

 occurred, which was indicated by a darkening in the colour 

 of the substances. The reactions involved are endothermic 

 and the author concludes that the application of mechanical 

 force can bring about such reactions. The results have 

 given rise to a controversy (168) with Spring, in which both 

 he and Lea claim to have been the first to show that 

 mechanical energy can be continuously transformed into 

 chemical energy. 



CHEMICAL ENERGY. 



Thermochemistry . — Most of the work in thermochemistry 

 has been concerned with the determination of thermal 

 constants and does not admit of general treatment. An 

 extensive investigation has been carried out by Stohmann and 

 his pupils (169), who redetermine the heats of combustion 

 of the fatty acids. Formic acid gives an exceptionally large 

 value, and thus exhibits the behaviour which in general 

 characterises the initial members of homologous series. 

 Amongst the general conclusions they obtain, the most note- 

 worthy are that on replacing H on a hydrocarbon by COOH 

 the thermal change is variable, and that acetic acid has 

 almost the same heat of combustion as malonic acid, and the 

 same is true for corresponding homologues of the two series. 



Berthelot ( 1 70) finds, as might have been anticipated, that 

 the heat of reaction of bromine and propylene differs from 

 that of bromine and trimethylene ; the latter is considerably 

 the larger. In another paper Berthelot has tried to reconcile 

 his principle of maximum work with modern views of 

 chemical energetics (171). 



In a suggestive paper, Nernst (172) shows that, in 

 general, on mixing two concentrated solutions which differ 

 only as regards concentration the change in the free energy 

 is equal to the change in the total energy of the system. 

 From considerations of the vapour pressure and heat of 

 dilution this is shown to be the case for solutions of 

 sulphuric acid. 



