104 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



fused chloride in the tube ; being, however, so bent, that it could not by any shake 

 of the hand or apparatus touch the negative electrode at the bottom of the vessel. 

 The whole arrangement is delineated fig. 14. 



790. Under these circumstances the chloride of tin was decomposed : the chlorine 

 evolved at the positive electrode formed bichloride of tin {77^-), which passed away 

 in fumes, and the tin evolved at the negative electrode combined with the platina, 

 forming an alloy, fusible at the temperature to which the tube was subjected, and 

 therefore never occasioning metallic communication entirely through the decom- 

 posing chloride. When the experiment had been continued so long as to yield a 

 reasonable quantity of gas in the volta-electrometer, the battery connexion was 

 broken, the positive electrode removed, and the tube and remaining chloride allowed 

 to cool. When cold, the tube was broken open, the rest of the chloride and the glass 

 being easily separable from the platina wire and its button of alloy. The latter when 

 washed was then reweighed, and the increase gave the weight of the tin reduced. 



791. I will give the particular results of one experiment, in illustration of the 

 mode adopted in this and others, the results of which I shall have occasion to quote. 

 The negative electrode weighed at first 20 grains ; after the experiment it, with its 

 button of alloy, weighed 23'2 grains. The tin evolved by the electric current at the 

 cathode weighed, therefore, 3*2 grains. The quantity of oxygen and hydrogen collected 

 in the volta-electrometer = 3"85 cubic inches. As 100 cubic inches of oxygen 

 and hydrogen, in the proportions to form water, may be considered as weighing 

 12*92 grains, the 3*85 cubic inches would weigh 0-49742 of a grain; that being, 

 therefore, the weight of water decomposed by the same electric current as was able 

 to decompose such weight of protochloride of tin as could yield 3-2 grains of metal. 

 Now 0*49742 : 3*2 : : 9 the equivalent of water is to 57'9, which should therefore be 

 the equivalent of tin, if the experiment had been made without error, and if the elec- 

 tro-chemical decomposition is in this case also definite. In some chemical works 58 

 is given as the chemical equivalent of tin, in others 57'9. Both are so near to the 

 result of the experiment, and the experiment itself is so subject to slight causes of 

 variation (as from the absorption of gas in the volta-electrometer (716.), &c.), that 

 the numbers leave little doubt of the applicability of the law of definite action in this 

 and all similar cases of electro-decomposition. 



792. It is not often I have obtained an accordance in numbers so near as that I 

 have just quoted. Four experiments were made on the protochloride of tin, the 

 quantities of gas evolved in the volta-electrometer being from 2*05 to 10'29 cubic 

 inches. The average of the four experiments gave 58*53 as the electro-chemical 

 equivalent for tin. 



793. The chloride remaining after the experiment, was pure protochloride of tin ; 

 and no one can doubt for a moment that the equivalent of chlorine had been evolved 

 at the anode, and having formed bichloride of tin as a secondary result, had passed 

 away. 



