188 



Prof. Dewar. On the Formation of [June 19, 



If we imagine some reaction — such, for example, as the combina- 

 tion of colouring matter with a tissue — influenced in one set of 

 experiments by nickelous sulphate, and in an altogether different set 

 by an equal weight of cobaltous sulphate, we can hardly conceive any 

 ground for the development of a reciprocal function, such as we have 

 experimentally traced. On the other hand, it seems reasonable to 

 suppose that, when two bodies are simultaneously confronted with 

 a single reagent, they both contend for its effect. Thus a chemical 

 antagonism may arise between them by virtue merely of their being 

 together ; and thence the reciprocal function. So far as we are aware, 

 the only other chemical function of the kind, hitherto investigated, is 

 to be found in Chizynski's* examination of the partial precipitation, 

 by ammonic phosphate, of mixed calcic and magnesic chlorides. 

 That chemist arrived at the conclusion, for which we consider his 

 evidence to be adequate, that " equal masses of calcic and magnesic 

 chlorides have always equal, but oppositely active, coefficients of 

 affinity." 



X. " On the Formation of Hydrocyanic Acid in the Electric 

 Arc." By James Dewar, M.A., F.R.S., Professor of 

 Chemistry to the Royal Institution. Received June 5, 

 1879. 



A series of experiments favouring the conclusion that the so-called 

 carbon lines are invariably associated with the formation of acetylene f 

 induced me to make some experiments to ascertain whether this sub- 

 stance can be extracted from the electric arc, which invariably shows 

 this peculiar spectrum at the positive pole, when it is powerful and 

 occasionally intermittent. For this purpose the carbons were used in 

 the form of tubes, so that a current of air could be drawn by means of 

 an aspirator through either pole, and the products thus extracted from 

 the arc, collected in water, alkalies, and other absorbents. Gases may 

 be led through one of the poles, and suction induced through the 

 other, in order to examine their effect on the arc. 



The following experiments record the results obtained by means of 

 the Siemens and de Meriten's magneto-machines. 



Experiment 1. — Drew a current of air by an aspirator through the 

 drilled negative carbon, and passed the gases through potash, and 

 iodide of potassium, and starch paste ; found no nitrites ; potash con- 

 tained sulphides. 



Experiment 2. — Hydrogen led in by the positive pole and the gases 

 extracted as above, gave the well-known acetylene compound with 



* Ann. Ch. Pliarm., Supp. iv, 226—253. 



t As suggested by Pliicker, Angstrom, and Thalen. 



