218 On some Comlinations of Plattna. 



platina + 18"26 sulphur. I found that a cubical inch of di- 

 stilled water, the barometer being at 30°, and thermometer 

 at 60', absorbed three cubical inches of sulphuretted hy- 

 drogen ; hence the eight grains would aljsorb about 0*34 

 of a grain; which added to the 4'56 grains =:4'9 grains. 

 Hence, lOO grains of hydrosulphuret of platina afforded 



Platina 6474 



Sulphur 18-26+ 4 = 22-26 



Sulphuretted hydrogen gas about 3-00 

 Water ' 800 



10000 

 The most probable idea of its constitution is perhaps 

 that it is compounded of the supersulphuret of platina and 

 sulphuretted hydrogen*, and the results appear to agree very 

 nearly with this supposition. According to my experi- 

 ments in the Philosophical Magazine for July, the super- 

 sulphuret of platina contains 28 percent, of sulphur. Now 

 100 grains of the hydrosulphuret appear to contain 64*74 

 grains of metallic platina, which would require 23-24 grains 

 of sulphur to be converted into the super-sulphuret. The 

 actual quantity obtained, amounts to about 22-26 grains. 

 These coincidences vi'ere rather unexpected, and are much 

 greater than could have been anticipated in experiments of 

 this kind. 



In the course of my experiments on the hydrosulphuret 

 of platina, I had occasion several times to observe a brown 

 precipitate produced in a solution of platina by sulphuretted 

 hydrogen in particular circumstances, especially when it 

 was made over mercury, by letting up a solution of pla- 

 tina into a jar of the gas. I made some unsuccessful 

 attempts to examine this substance, thinking its consti- 

 tution might be different from the hydrosulphuret I have 

 described. I found it rapidly changed colour in con- 

 tact with air, and became black: probably its composition 

 may be determined by comparative experiments on the 

 quantity of gas necessary to produce it. Should the results 

 I have obtained be confirmed by future experiments, we 

 shall probably become acquainted with a new class of com- 

 pounds of which nothing is at present known, consisiing 



* Since my paper went to press. I made the following experiment, which, 

 if it does not confirm the above idea, gives it a still higher degree of proba- 

 bility. A cubical inch of an aqueous solution of platina, exposed for about 

 two days in a receiver of sulphuretted hydrogen gas over mercury, absorbed 

 more than ten cubical inches of the gas. I found that a cubical inch of the 

 «ame solution of platina required about eight cubical Inches of hydrogen to 

 reduce the platina to the metallic state. 



of 



I 



