164 Proceedings. 



we have pv — constant, and the curve connecting/ and v is 

 an equilateral hyperbola. It will be remembered that the 

 temperature will change during the operation, and that this 

 is not a form of Marriotte's Law. Like the usual laws of 

 gases this is doubtless only an approximation to the actual 

 law. 



"Before leaving this subject, I would add that Hirn 

 considers that his experiments show that there is a 

 real measurable cohesion in both gases and vapours. 

 This force of cohesion he calls the internal pressure, and 

 considering what we usually call the pressure of a gas as 

 the difference between the intensity of the expansive action 

 of heat and this internal pressure, he is able from his experi- 

 ments to estimate it. For example, in the case of super- 

 heated steam at 15 '38 atmospheres and 200 , he finds the 

 internal pressure to be 3 atmospheres. In this way Hirn 

 proposes to explain how it is that while, in accordance with 

 Faraday's Law, a definite electric current will deposit from 

 metallic solutions an amount of metal proportional to the 

 chemical equivalents of these metals, the combination say 

 of 1 gram of oxygen with an element say of iron or zinc 

 does not produce even approximately the same amount of 

 heat as it should do if the act of chemical combination 

 corresponded definitely to an electric separation. By 

 considering chemical affinity and the cause of cohesion as 

 different things, acting independently in any combination, 

 the work done in a chemical action consists of two parts : 

 one in the change of position due to the chemical action, 

 and the other due to the change in the molecular attraction 

 or internal pressure. The heat due to the first is equivalent 

 to the electric action which accompanies the chemical action, 

 the heat due to the other is independent of it, and is com- 

 parable with that developed in the compression of a gas or 

 condensation of a vapour. Hirn's views regarding gases 

 and vapours appear to - be peculiar to him, and at variance 



