Royal Society. 309 



errors of the moment of inertia and of the inductor surface — nor 

 those of the intensity of the earth's magnetism, except so far 

 as concerns variations in this magnitude. On the other hand, 

 I have assumed sixfold the above amount as the error. 



I by no means maintain that with such a limit of error all 

 that is desirable is accomplished ; but without constructing en- 

 tirely new instruments, and without erecting special buildings, 

 it would be for the present difficult to exceed this limit. 



It must moreover be considered that an alteration of £ per 

 cent, in the conductivity of the ordinary metals is produced by 

 an alteration of 1° in temperature. 



[To be continued.] 



XXXVII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from p. 229.] 



June 19, 1873. — William Spottiswoode, M.A., Treasurer and Vice- 

 President, in the Chair. 

 HPHE following communication was read : — 

 •*- " On the Action of Electricity on Oases. — ~No. II. On the Elec- 

 tric Decomposition of Carbonic-Acid Gas/' By Sir B. C. Brodie, 

 Bart., D.C.L., E.B.S. 



In my previous experiments the maximum amount of ozone 

 obtained by the action of electricity upon pure oxygen passed 

 through the induction-tube of W. Siemens was about 20 per cent., 

 an amount which, under the conditions of the experiment, could 

 not be exceeded. It occurred to me as possible to replace the 80 

 per cent.' of oxygen unaffected by the action of the electricity by 

 an indifferent gas, and thus to effect the complete conversion of 

 oxygen into ozone. This idea was the starting-point of the fol- 

 lowing investigation. 



When pure and dry carbonic-acid gas is subjected in the induc- 

 tion-tube to the electric action, a certain proportion of the gas is 

 decomposed into carbonic oxide and oxygen, a portion of which 

 appears in the form of ozone. The presence of this ozone may be 

 detected by its odour and the characteristic oxidations produced by it. 



It was a point of fundamental importance to determine whether 

 the ozone thus generated was the same^in kind as that formed by 

 the action of electricity on pure oxygen, and whether the oxidations 

 referred to were exclusively due to it ; for it was quite conceivable 

 that under the peculiar circumstances of the experiment other sub- 

 stances capable of producing similar oxidizing effects might be 

 formed. Now, in the investigation before referred to, I had dis- 

 covered certain quantitative reactions of ozone by which this sub- 

 stance is discriminated from all other known gases, and by which 

 its presence may be detected and its quantity estimated. The 

 electrized carbonic-acid gas was examined by the aid of these re- 

 actions. 



