1825/J Method of analyzing Sulphate of Zinc. 365 



successive trials varied from 68*5 grains to 69*2 grains, and 

 nothing was given out but water. This I ascertained by making 

 the experiment in a retort, and collecting the water in a 

 receiver. ^ 



After the salt had ceased to give out water on the sand-bati^, 

 ^e crucible was transferred to a spirit lamp, and the heat gx^ 

 eiually raised to redness. Water was given off at first nearly 

 pure; but it was soon mixed with sulphuric acid fumes, and 

 the quantity of these fumes was greatest when the salt became 

 red-hot. The total loss of weight which 181*25 grainy of 

 crystaUized sulphate of zinc sustained when thus treated, varied 

 in different trials from 81*6 to 81-9 grains. The salt thus 

 treated did not dissolve completely in distilled water, and the 

 undissolved portion was always greatest when tjie loss of weigKt 

 was greatest. 



From these experiments, repeated about a dozen of times, I 

 concluded that 181*25 grains of sulphate of zinc do not contain 

 so much water as 81*6 grains, nor so little as 69*2 grains. . , 



The conclusions to be drawn from these experiments will be 

 better understood if we divide the quantities experimented on 

 by 10. If we do so, we find that 18-125 grains of crystallized 

 sulphate of zinc contain more ^Yater than 6*92 grains, but less 

 than 8*16 grains. I had previously satisfied myself that the 

 atomic weight of water is 1*125. Now six atoms of water 

 amount to 6*75, and seven atoms to 7*875. 8*16 exceed this 

 last number by 0*285, which is only a small fraction of an atom. 

 The conclusion which I drew from these experiments is, that 

 crystallized sulphate of zinc contains seven atoms of water, 

 that when placed on the sand-bath it gives out six of these 

 seven, and that the remaining atom cannot be separated without 

 taking along with it a portion of sulphuric acid. 



These conclusions, indeed, required to be verified by the 

 subsequent steps of the analysis. Meanwhile it was pro- 

 bable that 18*125 grains of sulphate of zinc contain 7.875 grains, 

 or seven atoms of water. ,^ I 



3. To obtain the oxide of zinc without loss from the sulph^e, 

 1 had recourse to a variety of methods, some of which were 

 more, others less successful. A few of these may be stated . 



(1.), The quantity of acetate of barytes necessary to decom- 

 pose a given weight of sulphate of znic was found to be^^i^- 



P^!y?&l?^^^:^^^^^ P^^^ ^*^^ ^'^ ^fy^t^^^^X. 7 u; // 9riT .S^ 

 d £i^Xio :) Acetate of barytes . . .4-fi^^lP/l/^.l(0.X^3itf5b9fiiijjdo. 

 J819V98 ill Sulphate of zinc . /.J^4ipm /Vi&ipP3gql>ilP259bwoq o:^ 

 Y^i^iq B isbff , ,. ,. iqsi biiB ^isqsq sflfiiold'io gbldi 



g-g^iV two salts bem g d issol ved m thes© propof ttons,.;^a nnx^d, 



jJlp .sulphate of barytes was collected on the filter, aiad the 

 Metatej9^l^i9ftliE^. evaporate4^t(^,jjte^g^3j^^ fiffift^bift^ 

 lBi9V9a fli Jrigiswlp gc;- aiwif^iom im ©vig oi b98«90 yarit 



