M. Achille Cazin on Internal Work in Gases. 99 



At the moment equality of pressure commences, the first part 

 is cold, the second is warm, and the third is in a condition 

 which depends on the friction which it has produced during the 

 expansion. Let us suppose that this friction is greater in one 

 experiment than in another ; then there is a greater heating in 

 the third part of the gas ; consequently the pressure p is greater. 

 If we notice a value p<p' with slight friction, we may observe, 

 with friction sufficiently great, p>p l (p 1 having, moreover, the 

 same value in both cases) . 



This is what occurred in my expeiiments : the portion of gas 

 which passed from reservoir A glided along the tubes a' a, a x d \, 

 and produced great friction, especially along the part a i a' v 

 because the molecules in this place had the greatest velocity. As 

 to the first two parts of the gas, their velocity was inconsiderable, 

 and they behaved almost as if the tubes a a', a l a\ had not 

 existed. 



By suppressing the tube a x a\, the friction was considerably di- 

 minished, and the increase of pressure was much less than before. 



These observations clearly demonstrate that the sides of the 

 canal X Y which join the two reservoirs exert an influence on 

 the curve of excesses of pressure h; this influence consists in 

 raising the minimum b of this curve (fig. 1). It ought to be 

 appreciable with the glass vessel (the neck of which was 12 cen- 

 tims. long), but is lessened as much as possible with the zinc 

 reservoir which was used in the actual experiments. The neck 

 of this reservoir was, in fact, very wide and very short (dia- 

 meter 5 centims., length 4 centims.). 



This influence was considerable in an experiment I made with 

 a stone vessel : the neck consisted of a wide glass tube; it 

 formed an ajutage 15 centims. long and 4 centims. thick, and 

 there was a little cement on the edges of the tube. The curves 

 obtained by means of this reservoir were generally of the form 

 a' b' b" c' (fig. 1). I was compelled to give up the use of it. 



I ought to remark that it must not be concluded, from the 

 curve m np, that friction occasions the creation of a quantity of 

 heat different from that which results from the destruction of the 

 velocities of the gaseous molecules under ordinary circumstances. 

 The final thermal effect is always the same in every case — such, 

 for example, as would be observed in a body of water surround- 

 ing the reservoirs. That which changes with the intensity of the 

 friction is the law of the pressures during the expansion, because 

 the succession of thermal and partial mechanical effects itself 

 changes. The conversion of work into heat is effected the more 

 quickly the more intense the friction. 



[To be continued.] 



H2 



