Faraday as a Discoverer. 191 
that electrode; or it may seize upon the substance of the elec- 
trolyte itself, and thus introduce into the circuit chemical ac- 
tions over and above those due to the current. Faraday sub- 
jected these secondary actions to an exhaustive examination. 
Instructed by his experiments, and rendered competent by them 
to distinguish between primary and secondary results, he pro- 
ceeds to establish the doctrine of “‘ definite electro-chemical] de- 
composition.” 
Into the same circuit he introduced his voltameter, which 
consisted of a graduated tube filled with acidulated water and 
provided with platinum plates for the decomposition of the 
water, and also a cell containing chlorid of tin. Experiments al- 
ready referred to had taught him that this substance, though an 
insulator when solid, is a conductor when fused, the passage of 
the current being always accompanied by the decomposition of 
the chlorid. He wished now to ascertain what relation this 
decomposition bore to that of the water in his voltameter. 
Completing his circuit, he permitted the current to continue 
until “‘a reasonable quantity of gas” was collected in the vol- 
= pete. . 
OB int, 
tameter, The circuit was then broken, and the quantity of tin _ 
liberated, compared with the quantity of gas. The weight of 
the former was 3-2 grains, that of the latter 0-49742 of a grain, 
Oxygen, as you know, unites with hydrogen in the proportion 
of 8 to 1 to form water. Calling the equivalent, or, as it is 
sometimes called, the atomic weight of hydrogen 1, that of oxy- 
gen is 8; that of water is consequently 8+1, or9. Nowif 
the quantity of water decomposed in Faraday’s experiment be 
represented by the number 9, or in other words, by the equiva- 
lent of water, then the quantity of tin liberated from the fused 
orid is found by an easy calculation to be 57-9, which is al- 
most exactly the chemical equivalent of tin. Thus both the 
Water and the chlorid were broken up in proportions expressed 
‘heir respective equivalents, The amount of electric force 
Which wrenched asunder the constituents of the molecule of 
petent, to wrench asunder the constituents of the molecules of 
the chlorid of tin. This fact is typical. With the indications 
of his voltameter he compared the decomposition of other sub- 
7 aenhmitte ; 
; humberless tests, He purposely introduced secondary actions. 
© endeavored to hamper the fulfilment of those laws — 
