8 ATOMIC WEIGHTS OF SODIUM AND CHLORINE. 



The final step in every case consisted, as usual, in mixing the 

 salt with amnionic chloride and ammonic chlorplatinate, fusing until 

 colorless, and decanting the fused mass from the residue. The ten 

 results agreed almost exactly, indicating that the preparations were, 

 at least, identical ; but, of course, the results are all in error, because 

 of the erroneous end-point. 



Only two preparations were used in the four experiments of 

 1881.* For one of these, impure sodic bicarbonate was neutralized 

 with hydrochloric acid. The salt, after three recrystallizations, was 

 repeatedly fused with ammonic chloride and chlorplatinate. f By 

 evaporating a solution of the resulting salt with chlorplatinic acid, it 

 was converted into sodic chlorplatinate without fractionation of any 

 kind. About nine-tenths of this material was dissolved in water. 

 Stas assumed that any potassic salt would not then dissolve ; but this 

 possibility is by no means excluded. The first lot of crystals from 

 the solution was decomposed and fused, and the resulting sodic chloride 

 used in the first two experiments. A second and third lot were also 

 obtained from the mother liquor of the first lot. The salt made from 

 the third lot was employed in the fourth experiment of 1881. Thus 

 there were only four crystallizations between the starting point (which 

 was admittedly impure) and the final product; and the first three of 

 these crystallizations were of common salt, isomorphous with potassic 

 chloride. In the third experiment of 1881 , the salt was made by neu- 

 tralizing pure acid sodic carbonate and repeatedly fusing with ammonic 

 chloride in platinum , with no fractionation at all . These specimens were 

 probably less pure than the earlier ones. 



Thus it appears that every preparation of Stas was fused in con- 

 tact with platinum, which was usually in a finely divided "nascent " 

 condition, or at least in the presence of decomposing ammonic chlo- 

 ride. The question is therefore important whether or not platinum can 

 dissolve in melted salt at the temperature of 8oo. We have found 

 that fused salt when pure has but a very slight dissolving effect upon 

 platinum, but in the presence of ammonic chloride or hydrochloric 

 acid at a red heat in the presence of air a noticeable quantity of plati- 

 num is dissolved, as is indicated by the loss of weight of the contain- 

 ing crucible. It seems likely, then, that Stas's material contained 

 traces of platinum, either in a very finely divided state or possibly as 

 a platinum salt ; but the amount could hardly have been large. Stas 

 invariably found non-volatile residues in his preparations, consisting 

 of silicates of sodium and calcium, which he discovered by vaporizing 

 the salt. These residues usually amounted to about 0.004 P er cent. 



*Oeuvres, 1,755. tOeuvres, 1,685. 



