124 Experiments on PL.llna. 



Jourlefs acid only is feen to rife, while the folution makes no 

 other progrefs than that of approaching towards concentra- 

 tion. 



When the heat had made the greater part of ihe fuper- 

 fluous liquids pafs over into the receiver, the nitrous gas 

 again Ihosved itfelf ; and it appeared to mc at this third pe- 

 riod, that the portion of the free acids, which had attained to 

 a certain degree of concentration, cxerciled a reaclion on the 

 crude pkitiiia. But I foon perceived that I could not depend 

 on this advantage; for, after having diluted in water the 

 faline niafs, to feparate the exccfs of the crude plalina, I 

 found that the pound of nitro-muriatic acid had dillolved 

 only J 6 drams and 12 grains of platina ; a quantity which 

 differs hy more than a dram from that of the tiiird experi- 

 ment: but notwithftanding this variation, it is not, as I have 

 faid, an eiglith above the other. 



The nitrous gas of this third period aives us reafon to 

 believe that it docs not difiisr in its origin from that obl'ervcd 

 in the concentration of metallic nitrates, when the latter ap- 

 proach condenfation. The augmentation of heat, therefore, 

 onlv decompofes a remainder of the nitric acid, from which 

 the red vapours in queftion refult. 



Let us now return to the diftillation. The liquor found in 

 the receiver weighed 10 ounces and i dram : it had no co- 

 lour, and by the areometer indicated onlv Q degrees ; while 

 the nitro-muriatic acid, which had produced it, indicated X3 

 before it was employed . The liquor is fonietimes feen fligluly 

 coloured, though the operation may have been conduced 

 with the ufual precautions ; becaufe the movement of the 

 ebullition is no doubt fr.fficicnt to throw a few drops of the 

 folution into the neck of the retort. This, on the whole, is 

 onlv a little platina, as is indicated -at the moment by the 

 cinnamon-coloured precipitate, occasioned bv the "hvdro- 

 fulphurated water. I'hefe acid products have no fenlible 

 a«Stion on the platina; but, to kjiow the advantage which 

 ought to be taken of them, I divided them into two parts, 

 of five ounces and half a dram each. 



I added to one of thcfe parts a ounces of muriatic acid, 

 to the other an equal ([uaniity of nitric acid; and thcfe two 

 new mixtures were treated, as ufual, wiih three ounces of the 

 fame crude platina. 



The firll diiiblved 4 drams and 16 grains of platina, which 

 would have approached 8' drams if I had empkived the 

 10 ounces and i dram of the product with the addition of 

 4 ounces of muriatic acid. 



The. fccond cculd diflblvc only 48 grain?, that is to fay, 



I dram 



