ZINC. 147 



Upon comparing Erdmann's results with those of Jacquelain two 

 points are worth noticing : First, Erdmann worked with purer material 

 than Jacquelain, although the latter applied corrections for the impuri- 

 ties which he knew were present ; secondly, Erdmann calcined his zinc 

 nitrate in a porcelain crucible, while Jacquelain used platinum. In the 

 latter case it has been shown that portions of zinc may become reduced 

 and alloy themselves with the platinum of the crucible ; hence a lower 

 weight of oxide from a given quantity of zinc, a higher percentage of 

 metal, and an increased atomic weight. This source of constant error 

 has undoubtedly affected Jacquelain's experiments, and vitiated his 

 results. In Erdmann's work no such errors seem to be present. 



Favre * employed two methods of investigation. First, zinc was dis- 

 solved in sulphuric acid, the hydrogen evolved was burned, and the 

 weight of water thus formed was determined. To his weighings I ap- 

 pend the ratio between metallic zinc and 100 parts of water : 



25.389 grm. Zn gave 6.928 grm. H 2 O. 366.469 



30.369 " 8.297 " 366024 



31.776 " 8.671 " 366.463 



Mean, 366.319, .088 



Hence Zn = 65.494. 



The second method adopted by Favre was to burn pure zinc oxalate, 

 and to weigh the oxide and carbonic acid thus produced. From the 

 ratio between these two sets of weights the atomic weight of zinc is easily 

 deducible. From Favre 's weighings, if C0 2 = 100, ZnO will be as given 

 in the third column below : 



7.796 grm. ZnO = 8.365 grm. CO 2 . 93. 198 



7-342 " 7.883 " 93-137 



5.2065 " 5.588 " 93-173 



Mean, 93.169, .012 



Hence Zn = 65,521. 



Both of these determinations are open to objections. In the water 

 series it was essential that the hydrogen should first be thoroughly dried 

 before combustion, and then that every trace of water formed should be 

 collected. A trivial loss of hydrogen or of water would tend to increase 

 the apparent atomic weight of zinc. 



In the combustion of the zinc oxalate equally great difficulties are 

 encountered. Here a variety of errors are possible, such as are due, for 

 example, to impurity of material, to imperfect drying of the carbon 

 dioxide, and to incomplete collection of the latter. Indeed a fourth 

 combustion is omitted from the series as given, having been rejected by 

 Favre himself. In this case the oxide formed was contaminated by traces 

 of sulphide. 



'Ann. Chim. Phys. (3), 10, 163. 1844. 



