Mr, Grove on the Decomposition of Water hy Heat. 95 



chemical affinity is only another mode of molecular attraction. 

 Thus a high degree of rarefaction, as at the bounds of the 

 atmosphere, or in the interplanetary spaces, may entirely 

 change the chemical condition of matter. 



In a paper published in the Philosophical Transactions for 

 1843, p. Ill, I have shown that we may oppose a chemical 

 action by a physical one (electrolysis by a vacuum), that an- 

 tagonizing chemical by physical tension, they mutually oppose 

 each other. 1 believe the converse of this experiment has 

 been made by M. Babinet, who by physical compression has 

 prevented the development of chemical action. 



I have also described in the Philosophical Magazine for 

 November 1845, certain phaenomena which appear to me to 

 be irreconcileable with received chemical views ; and though 

 I then believed that the theory of Grotthus would be obliged 

 to give way, I now incline to think that some of our chemical 

 doctrines must ere long undergo a revision. 



It is rather surprising that the valuable applications of which 

 the phaenomena of voltaic ignition are capable, and the fertile 

 field which (as I believe) it presents for discoveries, both phy- 

 sical and chemical, should have been so completely neglected. 

 It is true that until a recent period the imperfection of the 

 voltaic battery rendered accurate and continued experiment 

 on this subject difficult of performance, but still much might 

 have been done. Davy made several experiments on the 

 voltaic disruptive discharge, which in many points may be 

 regarded simply as very intense ignition \ but I am only aware 

 of two experiments of his on voltaic ignition; one, in which 

 he employed it in an exhausted receiver to examine to what 

 extent the i*adiation of heat was carried on in vnaio; and 

 another, already alluded to, in which, by immersing a portion 

 of an ignited wire in water, he observed that it conducted in 

 some inverse ratio to its heat. 



I have made a vast number of experiments on the voltaic 

 arc or disruptive discharge, in various media*; when this is 

 taken in a medium incapable of acting chemically on the elec- 

 trodes, the phaenomena are those of intense ignition of the 

 terminals, which are dissipated in vapour and condensed upon 

 the interior of the vessel in which the discharge is taken. 1 

 have examined some of these deposits, and they appear to 

 consist of the metal of the terminals in a finely-divided state ; 

 this is strikingly shown with zinc. If the arc be taken between 

 zinc points in an exhausted receiver, a fine dark powder, 

 nearly black, is deposited on the interior, which, when col- 

 lected, proves to be pure zinc, and on the application of a 



* Phil. Mag., June 1840 ; Literary Gazette and AthenEeum.Feb. 7, 1845. 



