38 K. D. Kraevitch on an Approximate Laic of the 



Ferric Alum {Ammonia). — Paper imbued with solution of 

 this salt, dried and marked, was immersed in solution of 

 potassium ferridcyanide. The marks came out blue, showing 

 that the ferric salt had undergone partial reduction. 



It is easily conceivable that the action of shearing-stress 

 should be enormously greater than that of simple pressure. 

 For it seems probable that pressure can only cause decom- 

 position when the resulting product is more dense, has a 

 greater specific mass, than the original substance. With 

 shearing-stress the case is altogether different. All matter is 

 in a state of vibration, and it is easily conceivable that the 

 forcible friction of a hard substance may increase vibration 

 in somewhat the same way as does a bow drawn over a 

 stretched cord. Both the elasticity and the tension of the 

 atoms themselves are vastly greater than those of any 

 stretched cord, so that the increased vibration may easily be 

 sufficient to shatter the molecule. 



The transformation of light, heat, and electricity into 

 mechanical energy, as well as the converse transformations, 

 are extremely familiar. That mechanical energy may be 

 transformed into chemical energy is proved by the results 

 described in these papers. The converse transformation, that 

 of chemism into work, is in an industrial point of view by far 

 the greatest chemical problem now awaiting solution. But it 

 is by no means certain that such a transformation is practi- 

 cally possible. At least it seems probable that the improve- 

 ment in our method of obtaining work from the chemism of 

 carbon may be in the direction of substituting electricity for 

 heat as the intermediary. 



IY. On an Approximate Law of the Variation in the 

 Pressure of Saturated Vapours. By the late K. D. Keae- 

 vitch*. 



THE dependence between the pressure of a vapour in a 

 state of saturation and the temperature is probably ex- 

 pressed by an exceedingly complex function, which, notwith- 

 standing the endeavours of many renowned physicists, has 

 not yet been determined. Even the interpolation (empirical) 

 formulae, with the exception of Biotas formula, cannot be 

 regarded as satisfactory. The cause of failure is to be found 

 in the endeavour to attain the dependence sought for in all 

 its exactitude, which is probably excessively difficult (if not 

 impossible) to do, because the pressure of a vapour in a state 



* Communicated by Prof. Mendele'eff. Translated by George Kamensky. 



