Attack on his " First Principles of Chemistry." 219 



state exactly what I got, and what I doubt not I should get 

 again were I to repeat the analysis. 



But this solitary analysis was not the only one from which 

 I deduced the atomic weight of oxide of zinc, tliough I thought 

 at the time, and still think, that it affords sufficient data for 

 the purpose. I may mention another here, which I made 

 about a year ago, and which was witnessed by one of my 

 practical pupils. 5-25 grains of pure oxide of zinc were 

 mixed with their own weight of flowers of sulphur, and heated 

 in a covered porcelain crucible over a spirit-lamp till the 

 crucible was made red hot. It was kept at that temperature 

 till all sulphur fumes had ceased to exhale. The crucible was 

 then allowed to cool. By this process the oxide was converted 

 into sulphuret of zinc. Its weight was 6-25 grains very nearly. 

 It rather exceeded 6-25, but was not so much as 6-26 grains. 

 Now the atom of oxygen is 1, and that of sulphur 2. It is 

 obvious that the Oxide must have been a compound of 



Zinc ^^-25 



Oxygen I 



5-25 



And the Sulphuret, of Zinc 4.'25 



Sulphur . . .2 



6-25 

 When this sulphuret was dissolved in muriatic acid it left a 

 trace of sulphur too small to be weighed, but visible to the 

 eye, and giving out a sensible odour of sulphurous acid when 

 heated. This slight surplus of sulphur was doubtless the 

 cause of the slight additional weight above 6-25 grains. 



Such an experiment could leave no doubt about the accu- 

 racy of my analysis of sulphate of zinc. The analysis of 

 blende which I made last year with great care, and repeated 

 four times, tends still further to corroborate the same thing. 

 As I have sent the result of my investigation of this mineral 

 to the Royal Society of Edinburgh, 1 do not consider myself 

 at liberty to detail it here. 



I had seen from the new edition of Dr. Turner's First 

 Principles of Chemistry, that Berzelius had announced my 

 number for barytes to be erroneous. But I have not yet seen 

 the paper in which this announcement is made, and do not 

 know what the alleged inaccuracy amounts to. I had found 

 the atomic weight of the -t alkaline earths to be 



Magnesia 2*5 



Lime 3-5 



Strontian 5*5 



Barytes 9*75 



2 F 2 Had 



