580 PROFESSOR DITTMAR AND MR JOHN M'ARTHUR ON 



appreciable proportion of oxygen ! (2 - 03 grms. gave 15*6 mgs.). Where this 

 oxygen came from we are unable to say ; perhaps it came out of the glass of 

 the combustion-tube. If Schonbein were still alive he would perhaps say that 

 the oxygen came out of the chloride of silver ; we need not add that this is 

 not our explanation of the phenomenon. 



While we are compiling this memoir, it strikes us that the oxygen in a chloro- 

 platinate might perhaps be determined by heating it, behind red-hot silver, in 

 a combustion-tube connected with, and previously evacuated by means of, a 

 Sprengel pump. The chlorine should be retained as AgCl, and the oxygen go 

 off as such (with the water), so that it could be collected, determined, and 

 identified by the methods of gas analysis. Unfortunately the idea did not 

 present itself to our minds at the time, and we had to rely on an obvious 

 indirect method for determining the oxygen of a chloroplatinate. This is what 

 we did in the following experiments. 



Supplement to Experiment V. of First Series. 



The principal chloroplatinate produced in this experiment,* while being dried 

 at 130°, became slightly discoloured from some unexplained cause. Hence, 

 instead of analysing it according to our general plan, we wrought it as follows : — 



The dried precipitate was dissolved in water in a large platinum basin, the 

 solution filtered, and the filtrate allowed to cool with occasional agitation. 

 The crystalline deposit was washed twice, each time with 10 c.c. of water. 

 It was then recrystallised from hot water. The crystals obtained were dried 

 at 120° C, weighed, dissolved in water, and reduced in hydrogen in the wet- way, 

 to determine the platinum and the two chlorines. 



The results were as follows : — 



Fixed Chlorine. Loose Chlorine. Platinum. Substance. 



Absolute weights, . 0-52125 1-02916 1-4374 35704 grms. 



Relative „ . Cl 2 = 70-91 140005 195-54 485-71 



= 3-9488 x CI 

 The chlorine-deficit is too great to be explained by observational errors ; 

 the salt must be assumed to have contained 0*0512 equivalents of oxygen, 

 instead of chlorine, per molecule. 



Admitting this, we have, for the composition of 48571 parts, 

 Platinum, 19554 



Chloride of {potassium, . 

 Other chlorine, 

 Oxygen (as hydroxyl), . 

 Water (in the hydroxyl), 



149-18 



14000 



041 



0-46 



485-59 



Total, 

 instead of 485*71, which is very satisfactory. 



* We mean the bulk of the original precipitate; i.e., that part of it which did not pass on the 

 filter, and which, as stated on page 570, amounted to 9-6244 grms. after drying at 130° C. 



