f 19 On some Comlinations of Platina. 



expelled at the moment of ignition, it almost precisely 

 agrees with the sul)siilph!iret. 



As the hydrosiilphiiret absorbed oxygen, became acid, 

 and attracted water when dried in the atmosphere; it is 

 evident that in such a state it could only furnish variable 

 results, depending entirely on the circumstances to whi.ch 

 it had been previously exposed. To obviate these diffi- 

 culties, it was necessary to have recourse to some mode of 

 obtaining it, by which the agency of the atmosphere would 

 be excluded. As I knew no practicable method of sepa- 

 rating the acid from the hvdiosulphuret and edulcorating 

 it with distilled water, out of the contact of the air, it be- 

 came necessary to determine with some degree of precision 

 the atrency of air and water on it. With these views, I 

 exposed a surface of recently made hydrosulphuret of pla- 

 tina (which had been well washed with distilled water, 

 and hastily dried with bibulous paper,) on a platina cover, 

 to a known quantity of oxygen gas ; after £0 hours th« 

 gas was scarcely diminished, and after about lU days only 

 l^jS^ths of a cubical inch were absorbed. 



Some of the above hydrosulphuret was also put into a 

 bottle lilled wiih distilled water; the water was occasionally 

 examined, but after some days no sensible quantity of sul- 

 phuric acid had been formed. 



These experiments seemed to prove that this substance 

 might be washed in contact with the atmospliere, without 

 xmderjioing any perceptible change in its constitution. 

 I shall now slate the mode I adopted to procure it. Into 

 a retort of about the capacity of 40 cubical inches, an ' 

 aqueous solution of muriate of platina was introduced ; it 

 was exhausted of air, and filled with sulphuretted hydrogen 

 gas ; a considerable absorption instantly took place, which 

 was much increased by agitation ; fresh portions of gas 

 were occasionally admitted, and the process was continued 

 until the fluid becanie nearly colourless. Bv this means 

 all the platina may after some time be separated from the 

 folution. The hydrosulphuret precipitated was of a uni- 

 form black or very dark brown colour, and exhibited in 

 goine places^ especially the film on the surface, tiie met'illic 

 lustre. It was now put on a filter, and washed with di- 

 stilled water till this fluid was tasteless, and did not affect 

 litmus paper; care being taken to keep it during this time 

 always covered with water. Whilst it wms yet quite moist 

 and the water still oozing through in drops, it was hastily 

 put into a tubulated retort, to which a stop-cotk had been 



previov^.sly 



