NOTES ON ATOMIC WEIGHTS. 207 



r 5*88 times that of hydrogen, the higher value being in all 

 probability the more correct. 



Having now satisfactory determinations of our funda- 

 mental ratio we still require other ratios to be able to de- 

 termine conveniently the atomic weights of many elements. 

 If an element forms many compounds with oxygen it is 

 never safe to conclude without the most rigorous proof that 

 we have a pure oxide absolutely free from the other oxides 

 of the same element. Hence determinations of atomic 

 weights made by the reduction of oxides to the element or 

 of one oxide to a lower one or of the oxidation of an 

 element to an oxide or of one oxide to a higher oxide must 

 always be accepted with caution. The use of the haloid 

 compounds (especially those of bromine), of many elements, 

 is of the greatest value, and for this we require an exact 

 knowledge of the ratio bromine : oxygen. For this we 

 depend chiefly on the classical work of Stas. The publica- 

 tion of the complete works (5) of J. S. Stas under the able 

 editorship of Professor W. Spring, of Liege, enables every 

 one now to obtain in an elegant and convenient form these 

 models and masterpieces of accurate research which were 

 formerly so difficult to procure. How great the contrast 

 between the work of Stas and too much of that turned out 

 at the present day a glance at almost any page of his 

 works will show. Every step was proved most conclusively, 

 however simple and even axiomatic it may seem to us now, 

 before he proceeded to more elaborate propositions and 

 deductions. For instance, in his Nouvelles Recherches he 

 begins by proving that ammonium chloride prepared from 

 absolutely different sources and purified in different ways 

 always contains exactly the same proportion of chlorine, 

 and that the same weight of each sample precipitated 

 exactly the same amount of silver from its solution in 

 nitric acid. He obtained his ammonia from ordinary sal 

 ammoniac after destroying any organic bases by a treat- 

 ment with aqua regia, and from commercial ammonium 

 sulphate by a similar purification, by heating it to a high 

 temperature with strong sulphuric acid, and then oxidation 

 with nitric acid, and from potassium nitrite by reduction in an 



