Combination of Gases by Platinum. 129 



preventer of cross precipitation ; for instance, if zinc and copper 

 be employed with muriatic acid but without diaphragm, putting 

 out of the question the pi'ecipitation of the zinc on the copper, 

 the power would be only as the excess of the affinity of chlorine 

 for zinc over its affinity for copper; with the diaphragm we 

 have no opposing current, the affinity of chlorine for copper, 

 assisted by that of hydrogen for oxygen, is able readily to 

 cause decomposition of the sulphate of copper and give rise 

 to a strong current. In the first or common arrangement, 

 this current opposes, and consequently, in estimating the re- 

 sulting power, must be deducted from that produced by the 

 superior affinity of chlorine for zinc ; in the last arrangement, 

 the thus evidently inferior obstacle, the resistance to decom- 

 position of the sulphate, is the only one to be overcome*. 



It would seem then that the best form of combination would 

 be one with two metals and two electrolytes, the generating 

 metal being one which has the strongest affinity for the anion 

 of the electrolyte in contact with it, wiiile the other solution is 

 most readily decomposable by its cation and does not cause a 

 precipitate upon which its own anion would readily react ; zinc 

 with muriatic acid and copper with sulphate of copper fulfil 

 these conditions to a great degree; if these principles be 

 correct, very superior combinations may be discovered. I 

 cannot refrain from expressing, with much diffidence, a hope 

 that these experiments may be thought worthy of verification 

 and extension by those "older in practice, abler than myself." 

 I remain, Gentlemen, yours, &c., 



W. R. Gkove. 



P.S.J«n. 1839. I should have pursued these experiments fur- 

 ther, and with other metals, but was led aside by some experi- 

 ments with diffiirent solutions separated by a diaphragm and 

 connected by platinum plates ; in many of these I have been 

 anticipated. 



I will however mention one which goes a step further than 

 any hitherto recorded ; and affords, I think, an important il- 

 lustration of the combination of gases by platinum. 



Two strips of platinum 2 inches long and three-eighths of 

 an inch wide, standing erect at a short distance from each 



• The reason why iron with sulphate of iron and muriatic acid is inferior 

 to the copper combination here described, may be that the difference of 

 afTuiitics is not so great, but more jjrobably proceeds from tlie minute cur- 

 rents on the surface of the iron weakening the efficacy of the chemical 

 action to produce a general current; copper being more iioniogeneous 

 evolves no hydrogen and the vviiole action is utilized. Co[)per with sul- 

 phuret of potassium and sulphate of cop|)er is a most powerful unimctal 

 combination, if unimetal it may be called. 



Vhil. Mag, S. 3. Vol. U. jVo. 86. I'cb. 1839. K 



