28 On the Action of 



suit was precisclv that which I had ohserved when my ope- 

 rations i'aik'd ahogeihcr, aud which of course was the most 

 frequent. Tins method was repeated tv\ ice. The second 

 tinie the precipitate of platlna and mercury was boiled with 

 muriatic acid, in order to free it horn is'on ; but the latter 

 trial \va:< -.lot more successful than the former. 



'J'hcir third cxperimeiU was what thev have called a re- 

 petition of that in which f had obtained palladium by pass- 

 ing a current of sulphuretted hydrogen gas through a njixcd 

 solution of platina and mercury. Their method was the 

 tbllouin^: — They dissolved 150 grains of platma with 450 

 of mercurv, and added a solution oF hydro-sulphuret of 

 potash. They obtained a precipiiate which, at first, v.'as 

 black, afterwards gray; but the v, hole became black bv 

 bcina; stirred. To be certain that all the metal was preci- 

 pitated, thty added an excess of sulpharet of potash, and 

 perceived that a part of the precipitate was rcdissolvcd. The 

 li'quor was then filtered, and to that part of it v/hich con- 

 tained the rcdissolvcd precipitate an acid was added. From 

 this process they obtained a yt^How precipitate weighing 91 

 grains ; and 50 grains of this, exposed to a strong heat, 

 left 3-8ths of a grain of platina. Thev obtained no palla- 

 diinii from that part of the precipitate which had not been 

 redissolved ; ana the result of the experiment was complete 

 failure. 



I shall not make any observation upon the issue of this 

 process, since, in this case, the best conducted is but too 

 liable to be unsuccessful, and that without any apparent 

 fault in the operator. Bat as it has been given as a repeti- 

 tion of one of mine, it may not be fruitless to examine how 

 far the repctitl(.'n was exact. 



I had passed a current of sulphuretted hydrogen gas 

 through a mixed solution of platma and mercury, by which 

 means thev were precipitated together. My object was so 

 iiitimately to combine sulphur with these metals, that when 

 exposed to heat they might (if I may be allowed the ex- 

 pression) be in chemical contact with it at the moment of 

 their nascent metallic state; and as a low temperature suf- 

 fices, as well to reduce those metals as to combine palla- 

 dium with sulphur, 1 hoped that those efiects might be 

 produced before the total dissipation of the mercury. How 

 far my expectation was fulfilled has been stated in my former 

 paper. 



The sulphuretted hydrogen gas \\hich Mersrs. Eosc and 

 Gchlcn presented to those metals was combined with pot- 

 ash. JSow, in the coyrse of dociniastic lectures annually 



delivered 



