334 Dr. P>. Ilassolbertf on the 



*-> 





its elements under the influence of the electric, disoharge. 



On the other hand, compounds arc formed under the same 

 influence; and between those opposite actions there is pro- 

 duced in certain cases a condition oi' unstable equilibrium, in 

 which no further change is produced by the continued action 

 of tho electric current. Acetylene, amongst others, is, ac- 

 cording to Uerthelof, one of the bodies which behave in this 

 way. [f a continuous series of electric discharges be sent 

 through this gas, decomposition occurs, which, however, is 

 not complete, but ceases at a. certain point, depending upon 

 the pressure at which the composition of (he gaseous mixture 

 remains the same. (Since, moreover, with constant change 

 of pressure the percentage composition of this mixture 

 does not change gradually but suddenly, this composition is 

 within certain limits independent of the pressure. Tims, i\)v 

 example, IJorthelot found in 100 volumes of the resulting 

 mixture, at a pressure of from 3* l(> to 0*1 1 metres of mercury. 

 12 volumes of acetylene; at 0*31 metre, (rf) volumes; and 

 between 0*23 and (M0 metre, 3\ r ) volumes : the last mixture 

 retained its stability even at a pressure of only a lew millimetres. 

 We see from this thai the equilibrium between acetylene, 

 carbon, and hydrogen in the resultant gas-system changes 

 Only abruptly with the pressure in multiple proportions ; and 

 since, consequently, those 4 complications which would other- 

 wise result by continuous change in the composition of the 

 gas under the influence of the discharge are, for the most 

 part, avoided, l>orthelof and Richard have justly regarded 

 the spectroscopic examination of this and similar mixtures as 

 specially adapted to give clearer evidence as to the spectro- 

 scopic conditions of compound bodies. The results of these 

 investigations, so far as the mixture of gases at present under 

 Consideration is concerned, on the int.erpreta.tion given to 

 them by Bertholot and Richard, can hardly be brought into 

 agreement with the results of later spectroscopic research, 

 and consequently cannot, in my opinion, be made to servo as 



an argument against the admissibility of Pliicker's view of 

 iho second hydrogen spectrum* 



The mixture employed contained l"7 per cent, of acetylene, 

 and 98*3 per cent, of hydrogen. These proportions were so 

 chosen in order to be as far as possible from the limits given 

 above. The gas having been introduced, under a. pressure of 



a few millimetres, into a Greissler's tube, the disoharge of a 



powerful induction-coil was passed through the tube, and the 



spectrum observed, [t is described * by Berthelotand Richard 



as follows :-- 



* Lor. cit. p. 1648. 



