1821.] of the Atoms of Copper ^ Zinc, Iron, Manganese, Sfc. 247 



Dissolve in another portion of that Hquid 13'25 grs. of pure 

 chloride of barium. Mix together the two solutions, and let the 

 precipitate subside. The clear supernatant liquid is neither 

 affected by muriate of barytes, nor by sulphate of soda ; conse- 

 quently it neither contains sulphuric acid nor barytes. It is 

 obvious from this that 17 grs, of sulphate of zinc contain exactly 

 five grs. of sulphuric acid. These facts v^arrant the conclusion, 

 that the composition of crystallized sulphate of zinc is a& 

 foUovv^s : 



1 atom sulphuric acid = 5*00 



1 atom oxide of zinc = 5-25 



6 atoms water = 6*75 



Thus it appears that an atom of oxide of zinc weighs 5'^5'; 

 consequently zinc itself must weigh exactly 4-25. 



It may, perhaps, be objected that my method of determining 

 the quantity of water in the salt might not be absolutely cor- 

 rect, as I had no means of determining whether the residual salt 

 retained any water or not. But let it be remembered that the 

 sulphuric acid in 17 grs. of the salt is exactly five grains, that 

 the oxide of zinc certainly approaches five in weight, and that if 

 we suppose the water to be increased by another atom, its 

 weight, would amount to 7'875 grs. leaving only 4*125 for the 

 weight of an eitom of oxide of zinc, which we are perfectly certain 

 from preceding experiments is greatly below the truth. It can- 

 not then be doubted that the atom of oxide of zinc weighs 5*25 ; 

 consequently the weight of the atom of zinc must be 4*25, or a 

 very little more than 1 had concluded from the previous experi- 

 ments of Berzehus and myself. 



III. Iron. 



It is well known that iron unites with two doses of oxygen, 

 and forms two oxides, the black and the red ; the oxygen in 

 which bear to each other the ratio of 2 to 3. This led at first to 

 the supposition that the black oxide of iron was a compound of 

 one atom iron + two atoms oxygen, and the peroxide of one 

 atom iron + three atoms oxygen. It vs^as under this impression 

 that Mr. Dalton fixed the weight of an atom of iron at 6^ ; but 

 when we examine the salts of iron, we do not findthemt o accord 

 with this view of the subject. Thus sulphate of iron( aostracting 

 the water) is a compound of 5 sulphuric acid + 4*5 black oxide 

 of iron. Now if we dissolve 9*5 grs. of anhydrous sulphate of 

 iron in water, and 20*75 of dry nitrate of lead in another portion 

 of water, and mix the two liquids together, we find that two new 

 salts are formed, both of which are neutral; namely, sulphate of 

 lead, and nitrate of iron; so that 4*5 grs. of black oxide of iron 

 just neutralize 6*75 grs. of nitric acid. We can have no doubt 

 from this that an atom of protoxide of iron weighs 4*5, or nearly 



