76 M.i. J. Rose-Innes on the 



cury is poured ofl. leaving a circular film upon the upper 

 surface of the pap-jr. On unfolding the sheet, a blackish 

 substance is found distributed through it, graduated from the 

 positive towards the negative pole. 



(2) If a sheet of tinfoil is included within the folds of 

 filter-paper, while the battery is applied, the tinfoil becomes 

 perforated with pin-holes. This, however, must not be taken 

 per se as a proof of any direct transition of metallic mercury 

 through the diaphragm ; for if, instead of the mercury con- 

 tained in the ring, a sheet of metal is used as the upper elec- 

 trode, pinholes still appear in a sheet of tinfoil included in 

 the folds of damp filter-paper. Moreover, if a sheet of tinfoil 

 is used as the upper electrode, this also becomes perforated. 



(3) Again, if the sheets of tinfoil are removed, and a gold 

 coin is used for the upper (positive) electrode, upon the top 

 of the damp filter-paper, the current produces a gold discolo- 

 ration which penetrates the folds. I have not yet had time 

 to examine this result, but it seems to throw some light upon 

 the formation of metallic lodes and veins. And although the 

 discoloration is the effect of a steady current, and not sparks, 

 it may help to explain the " inductoscripts"* of Mr. F. J. 

 Smith. 



X. On the Isothermals of Isopentane. 

 By J. Rose-Innes, M.A. } fi.Scj 



HPHE recent publication by Prof. Sydney Young of a long 

 I series of researches on i-opentane (Proc. Phys.. Soc. 

 Session 1894-95, pp. 602-657) offers a great opportunity to 

 those interested in the theory of gases. Since isopentane is 

 a saturated hydrocarbon, there seems to be a reasonable hope 

 that we are here dealing with a substance which will not 

 tend to form complex molecules at low volumes, and whose 

 behaviour may therefore be treated as normal ; and this fact, 

 together with the wide range of volume over which the expe- 

 riments have been conducted, renders Prof. Young's results 

 well fitted to test the various formulae that have been from 

 time to time proposed. Among these formulas there is none 

 more important than that formerly suggested by Prof. Young 

 himself, in conjunction with Prof. Ramsay, that the pressure 

 of a gas kept at constant volume is a linear function of the 

 temperature ; and the bearing of the experimental results 



* "Inductoscripts," by F. J. Smith, Proc. Phys. Soc. vol. xi. p. 353 

 (1892). 

 t Communicated by the Physical Society: read May 28, 1897. 



