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 4 . ZnO. Per cent. ZnO. 



6.699 3.377 5 -4io 



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,f there is a peculiar complication. After testing and criti- 

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

 K 2 ZnCl 4 , 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 readily, 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, Marignac 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 ZnCl 2 and KC1 in the 

 substance analyzed. 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, Cl 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 carefully dried K 2 ZnCl 4 . 

 The values for Zn are as follows : 



6. Two titrations N . Zn = 65.28 



7. Two titrations 65.39 



8. One titration 65.32 



* Ccmpt. Rend., 97, 906. 1883. 

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



