336 Dr. Faraday's Experimental Researches in Electricity. 



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 decomposing 

 chloride. When the experiment had been continued so long 

 as to yield a reasonable quantity of gas in the volta-electro- 

 meter, the battery connexion was broken, the positive elec- 

 trode 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 elec- 

 trode 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 elec- 

 tric current as was able to decompose such weight of proto- 

 chloride 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 electro-chemical de- 

 composition 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 (71 6.), 

 &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 num- 

 bers 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 mo- 



