RICHARDS. — A TABLE OF ATOMIC WEIGHTS. 299 



adduce experimental evidence in proof of this view, but Seubert showed 

 in his reply * that their hypotheses can hardly be applied to his deter- 

 minations. Most of Seubert's and Halberstadt's inconsistencies may be 

 explained by the supposition that the complex salts, like all substances 

 crystallized from aqueous solution, contain traces of mother liquor held 

 in minute cells within the crystal structure, and that these traces of 

 water are not set free until the substance is disintegrated, I have 

 accumulated a large amount of experimental evidence, soon to be pub- 

 lished, upon this subject. Water is one of the most dangerous, although 

 one of the least heeded, impurities in this kind of work ; and in my 

 opinion it is responsible for the lack of agreement in this case. Hence 

 the best data for the calculation of the atomic weight of platinum seem 

 to be those concerning the relation of the metallic platinum to the 

 potassic chloride or potassic bromide formed by the decomposition of 

 the complex salts : for the water must surely have been expelled from 

 these products of the ignition. According to Clarke f potassic platin- 

 chloride yields 40.101 per cent of platinum and 30.671 per cent of 

 potassic cliloride, — the means of the closely agreeing results of Seubert 

 and Halberstadt, — while according to Halberstadt potassic platinbro- 

 mide yields 25.915 per cent of platinum and 31.591 per cent of potassic 

 bromide. Disregarding the weight of the complex salt, and assuming 

 that KCl = 7-4.595, and KBr = 119.095, it is easy to calculate the 

 respective values 195.06 and 195.39 for platinum. The mean of these 

 two values, 195.2, is given below, instead of Clarke's 194.89. The pos- 

 sible occlusion of potassic halide by the complex salt may render even 

 195.2 too low; but more investigation is evidently needed to prove this. 



The same errors may enter into the work on other platinum 

 metals ; indeed Seubert t admits that traces of water were contained 

 in some of his salts, but he applies no correction for this serious cause of 

 inaccuracy. Since, however, Clarke's method of combining the discord- 

 ant results seems more nearly to eliminate the error in these cases, his 

 values for these elements are but little changed in the following table. 



Feeling wholly unable to decide the present controversy between the 

 two conflicting values (184.9 and 184.0) now proposed for tungsten, 

 I have chosen the mean, 184.4, as a compromise which cannot be much 

 more than 0.3 per cent out of the way.§ 



* Berichte d. d. cheni. Gesell., XXI. 2179. 



t Recalculation, page 333. 



t Liebig's Annalen, CCLXI. 262. 



§ Compare Hardin, Journ. Am. Ch. Soc, XIX. 657. (1897.) 



