﻿478 Intelligence and Miscellaneous Articles. 



Since the battery produces a deflection of 480 millims., the elec- 

 tromotive forces are 



I=— =iL. =0-00052, 

 48000 



P=_J^_ =0-000312. 

 48000 



We thus see that, using amalgamated zinc electrodes, sulphate of 

 zinc gives considerable inequality and polarization if it contains free 

 sulphuric acid and the resistances are small, but that the former is 

 reduced to a quarter and the latter to zero if the free acid is neutra- 

 lized with carbonate of zinc. — Arch, des Scienc. Phys. et Nat. Nov. 

 1868. 



ON A DEVELOPMENT OF HEAT WHICH ACCOMPANIES THE 

 BURSTING OF THE PRINCE RUPERT^S DROPS. BY M. DUFOTJR. 



The bursting of a Prince Rupert's drop is accompanied by a vio- 

 lent projection of the substance of the glass. A molecular repul- 

 sion seems to be produced in the interior of the body, which is strong 

 enough to impart to the separating particles a great velocity. At 

 the moment, of explosion there is a considerable development of vis 

 viva, quite out of proportion to the feeble mechanical effort consumed 

 in bursting the point. From the latter point of view, the Rupert's 

 drops suggest a problem concerning the mechanical theory of heat ; 

 and it is natural to inquire whether the work which accompanies 

 this explosion is not accompanied by calorific phenomena. 



At first sight it would seem as if there were some analogy be- 

 tween the separation of the vitreous particles in a bursting drop 

 and the sudden dilatation of a gas which expands after compression. 

 The small amount of work which consists in opening a stopcock 

 renders possible a considerable amount of work in the expanding 

 gas, just as the small effort necessary to break the point of a tear 

 gives rise to the reduction to powder and the projection of a large 

 mass of glass. Yet between these facts, the analogy of which I 

 point out, there are so many differences of an essential character, 

 that we cannot predict whether the explosion of the Rupert's drops 

 is accompanied by thermal phenomena like those which accompany 

 the expansion of a gas. 



This thermomechanical problem, which is difficult to discuss 

 a priori, appeared important enough to merit some investigation ; 

 and I have endeavoured to ascertain whether the^; explosion is ac- 

 companied by a change in temperature of the substance of the 

 glass. 



In a first series of experiments a thermo-electric apparatus was 

 used, to ascertain whether there was any difference of temperature 

 between the drops and the powder they produce. All the results 

 agreed, and showed a heating of the substance of the glass ; the 

 method employed did not enable me to measure with accuracy the 

 increase of temperature, which, moreover, was very slight. 



In a second series of experiments the drops were broken in a small 

 brass vessel containing oil of turpentine, which received the powder 



