246 Dr, ThomsuH*s Experiments to determine the Weight [April, 



Philosophy, }iv'u 330), will find that chloride of barium is com- 

 posed of 



1 atom chlorine = 4*5 



1 atom barium = 8-75 



13-25 



And that when this salt is dissolved in water, it becomes muriate 

 of barytes composed of 



1 atom muriatic acid .... = 4-625 

 1 atom baiytes = 9*75 



14-375 



Dissolve ill a minimum of distilled water 31'25 e;rs. of blue 

 vitriol, quite pure, dry, and in crystals. In another vessel 

 dissolve lo-26 x 2 = 26-5 grs. of chloride of barium. Mix 

 the two solutions together, and allow the mixture to stand 

 till the precipitate has fallen down, and the supernatant liquor is 

 quite clear. Examine this liquor by mixing it with muriate of 

 barytes and with sulphate of soda in two separate vessels. If 

 the experiment has been properly conducted, the liquid will not 

 be in the least altered by either of these reagents, showing 

 clearly that it contains neither sulphuric acid nor barytes. 

 Hence it is clear that the quantity of sulphuric acid (two atoms) 

 in 31*25 grs. of blue vitriol is just saturated by the quantity of 

 barytes (two atoms) in 26-5 of chloride of barium. If, instead of 

 31*25 grs, of blue vitriol, you take only 31 grs. or even 31*125 

 grs. the liquid will be found to contain an excess of barytes. 



If 31-25 grs. of blue vitriol'be dissolved in water, and a plate 

 of zinc put into the solution, the copper will be precipitated, and 

 it will be found to weigh exactly eight grains. 



II. Zinc, 



Many attempts have been made by chemists to determine with 



precision the atomic weight of zinc. Those of Berzelius and my 



own will be found in an early volume of the Annals of Fhiloso- 



:phy. I had deduced from these experiments 4* 125 as the weight 



of an atom of zinc. Dr. Wollaston*s weight, 4*1, may be consi- 



;<dered as nearly the same with mine. Dr. Prout fixed the weight 



%t 4, chiefly from theoretical considerations. The following 



'experiments will show that all these determinations are under 



the truth. 



Sulphate of zinc, or white vitriol, as it was formerly called, is 

 a salt, which crystallizes in four-sided prisms, and is transpa- 

 rent. It may be freed from its water by a cautious exposure to 

 a red heat; and 17 grs. of the crystals, when thus treated, lose 

 exactly 6*75 grs. Of course the residual salt weighs 10-25 grs. 



Dissolve 17 grs. of crystals of sulphate of zinc in water. 



