Mr Skinner, On the Electro-chemical equivalent of Carbon. 267 



§ 5. A theoretical explanation of the production of carbon 

 dioxide is required in the case of the electrolysis of pure water 

 (Bartoli and Papasogli, loc. cit.) of dilute sulphuric acid (Faraday, 

 Experimental Researches, vol. I. section 744) and of potassium 

 permanganate solution. 



Bartoli and Papasogli used distilled water, and an electromotive 



+ 

 force of 1200 volts. The ions in distilled water are OH and H, 



and when the OH ions combine with the carbon it is possible that 

 an orthocarbonic acid C (OH) 4 is at first formed, and that this 

 breaks up into C0 2 and 2H 2 0. Orthocarbonic acid has not been 



isolated although its ethereal salt has been prepared. In the case 



- + 



of dilute sulphuric acid with its ions HS0 4 and H we may suppose 

 that an unstable compound C (HS0 4 ) 4 is formed at first, and that 

 this immediately breaks up in aqueous solution forming C0 2 and 



4H 2 S0 4 . Similarly in KMn0 4 solution, where the ions are Mn0 4 



+ 

 and K, we must suppose that C (Mn0 4 ) 4 is an intermediate product 

 which reacting with water produces C0 2 and 4HMn0 4 . The 

 solution of carbon is here regarded as analogous to the solution of 

 the zinc in a simple voltaic cell. 



The formation of CO appears to be controlled by the current 

 density. The results in Table I. show that with a low current 

 density less CO is formed than with a high density. The nature 

 of the negative ion has an influence, since Cohen found that only 

 70 per cent, of the gas given off from warm fairly concentrated 

 sulphuric acid was C0 2 , and 29 per cent, was CO. The lowest 

 percentage with permanganate and bichromate was 77 per cent. 

 No organic compounds were found deposited or in solution in my 

 experiments. 



The solution of the quantity of zinc in a simple cell which is 

 accompanied by the flow of a unit quantity of electricity may be 

 regarded as the electro-chemical equivalent. In this sense these 

 experiments give a value for the electro-chemical equivalent of 

 carbon three times that of hydrogen, since twelve parts by weight 

 of carbon enter into combination when four parts by weight of 

 hydrogen are set free. 



