CRITICAL EXPERIMENTS FOR DETERMINATION OF POTASSIUM, ETC. 625 



of the R 2 , and hyclroxyl or oxygen instead of part of the Cl 6 ; that, in short 

 they were mixtures of the general composition PtOl^^ (OH)^ + (R 2 _yH.y), and 

 we deemed it worth while to try and reduce the y to nil by using chloro- 

 platinate of sodium as a precipitant and the "a," by heating the precipitate in 

 a current of dry hydrochloric acid. 



In accordance therewith (St Petersburg) platinum solution equal to 1*100 

 grms. of metal was evaporated with 07616 grm. of chloride of sodium, i.e. 

 1"15 Na 2 Cl 2 for 195 of platinum, to dryness on a water-bath, the residue 

 redissolved in 20 c.c. of water, and added to the chloride of rubidium 

 solution to produce a mixture containing about 0*68 grm. of surplus chloride 

 of rubidium by calculation. The mixture was allowed to stand over night, and 

 the precipitate then washed by decanting filtration, first with water, then with 

 50 per cent, and lastly with absolute, alcohol. The greater part of the dried 

 precipitate was transferred to a large porcelain boat, and in it, within a 

 combustion tube drawn out at the exit end, kept in a current of air, dried with 

 oil of vitriol, at 120° C, until its weight became constant, which took about six 

 hours in all. The weight of the dried chloroplatinate was 27791 grms. The 

 salt was then replaced in the combustion tube, a U-tube filled with glass beads 

 moistened with vitriol attached to the exit end by means of a short india-rubber 

 joint (see section on determination of water, page 578), and this joint next 

 kept at 120°, in a current of dry air, until the U-tube ceased to gain weight ; 

 the U-tube consisted entirely of glass. The air was displaced by dry carbonic 

 acid, the latter by hydrochloric acid, and this gas allowed to act at 120° C. 

 for 3^ hours. The hydrochloric acid was then displaced by carbonic acid at 

 50°, and the latter by dry air, at the same temperature. The boat had gained 

 - 5 mg., the sulphuric acid U-tube 6*4 mgs. The contents of the latter, when 

 diluted largely with water, and tested with nitrate of silver, gave a mere 

 opalescence of chloride of silver. Hence the 6;4 mgs. of a gain were water, 

 and, assuming that the substance lost water, and hydroxyl with formation of 

 water (HO + HC1 = H 2 4- CI), the water expelled amounted to 3 # mgs., 

 and the hyclroxyl replaced by chlorine to 321 mgs. and the chlorine taken 

 up in place of the latter to 67 mgs. The chloroplatinate was kept over solid 

 caustic soda for a night, to remove any adhering HC1, but it suffered no loss of 

 weight. For its analysis, it was dissolved completely in hot water, reduced by 

 hydrogen, &c. As there was not sufficient material for duplicate analyses, the 

 total and the fixed chlorine were each determined twice in the same quantity 

 of solution, viz., gravimetrically, and again by determining the weight of 

 unprecipitated silver titrimetrically. The results reduced to 2C1 parts of fixed 

 chlorine were as follows : — 



M = 581-37 ; platinum = 194*35 ; loose chlorine = 139*81, = 39434 x CI. 

 Hence we have for the composition of M parts — 



VOL. XXXIII. PART II. 4 Y 



