148 THE ATOMIC WEIGHTS. 



Baubigny,* in 1883, resorted to the well-known sulphate method. 

 Zinc sulphate, elaborately purified, was dried at 440° to constant weight, 

 and then calcined at a temperature equal to the fusing point of gold. 

 These data were obtained : 



ZnSO^. ZnO. Per cent. ZnO. 



6.699 3.377 50.410 



8.776 4-4245 50-416 



Mean, 50.413, ± .0020 



Hence Zn = 64.909. 



In Marignac's determinations of the atomic weight of zinc, published 

 also in 1883,t there is a peculiar complication. After testing and criti- 

 cising some other methods, he finally decided to study the double salt 

 KjZnCl^, which, however, is difficult to obtai n in absolutely definite con- 

 dition. Although the compound was purified by repeated crystalliza- 

 tions, it was found to deliquesce readil}^, and thereby to undergo partial 

 dissociation, losing chloride of zinc, and leaving the porous layer on the 

 crystalline surfaces richer in potassium. In order to evade this diffi- 

 culty, jNIarignac placed a large quantity of the salt in a funnel, and col- 

 lected the liquid product of deliquescence as it ran down. In this 

 product he determined chlorine by volumetric titration with a standard 

 solution of silver, and also estimated zinc by precipitation with sodium 

 carbonate, and weighing as oxide. From the data thus obtained equa- 

 tions were formed, giving for each a nalysis an atomic weight of zinc 

 which is independent of the proportion between ZnClj and KCl in the 

 substance analj^zed. The data unfortunately are too bulky for repro- 

 duction here and the calculations are complex ; but the results found for 

 zinc, when Ag = 107.93, CI = 35.457, and K ^ 39.137, are as follows : 



1. One titration Zn ^= 65.22 



2. Two "titrations 65.37 



3. Two titrations 65.31 



4. Two titrations 65.28 



5. One titration 65. 26 



Each of these values represents a distinct sample of the deliquesced 

 material, and the number of chlorine determinations is indicated. 



A second set of determinations was made by the same analytical 

 method directly upon the recrystallized and carefull}^ dried KjZnCl^. 

 The values for Zn are as follows : 



6. Two titrations Zn ^ 65 28 



7. Two titrations 65.39 



8. One titration 65.32 



* Ccmpt. Rend., 97, 906. 1S83. 

 tArch. Sci. Phys. et Nat. (3), 10, 194. 



