( 



Exp^rhncnfs on PJat'nia. Iig 



was accidentally at that degree of faturation which could 

 conduft to tliis difcovery; and this circuniltarice, as will be 

 fecn, is the firll of thofe ncceflliry for the fuccefs of the cryf- 

 tal ligation in qucftion. 



The fecond condition confiils in not leaving an excefs of 

 acid; and tliis Lewis accomplifhcd ; for he i'avs (p. 148) 

 that the favour of thefe crvftals was harfli and dirairrefablc, 

 but much Jefs corrofive than he expefted, on account of the 

 great quantitv of acid which he had employed. Indeed, if 

 this folution be prepared in the fame manner as prepared by 

 Lewis, it will be found to have the favour of four vegetables ; 

 and whatever difagreeable tafle it has, arifes from the iron 

 and copper. 



The muriate of platina, when pure, eafily cryftallizes ; 

 but it is difficult to make it crvftalfizc when it is united 

 with foreign muriates not fufceptible of cryrtallization, and 

 which oppofe this tendency. In this tlicre is nothino- 

 which diftinguiflies it from the moft cryflallizable falts, and 

 therefore we mu(t endeavour to difcover means for difen- 

 gaging it from thefe obftacles. We (liall now examine 

 thofe which may remove the excefs of acid from a folution 

 of platina. 



Every folution wbich has been fubjecled to ebullition and 

 concentration is not charscd with muriatic acid, and the 

 caufe may be eafilv perceived : but the cafe is not the fame 

 with the nitric acid, wliich fuffers ilfelf to be concentrated; 

 and though it is not att railed by the oxides, which the mu- 

 riatic acid feizes upon exclufively, it adheres to them with 

 fufficient force ; but if it be difficult to expel it, it may be eafily 

 decompofed. 



To accomplifli this, a little muriatic acid and crude platina 

 muft be added to the folution before it be diftilled. This 

 acid, which cannot aft upon the platina until it has been 

 oxidated, at the cxpenfe of the nitric acid, determines the 

 decompofition of the latter, and facilitates the feparation in 

 the form of nitrous gas. This operation mav be repeated,' 

 and when no more gas appears you may be allured that you' 

 have a folution difengaged from every excefs of acid. When 

 the folution is brought to this term, nothing but muriates 

 different from that of platina can retard the crvrtallization : 

 thefe muriates are thole of copper and iron oxydattd to a 

 maxiimim. 



To fe|)arate them, it is indifpenfably necelTary to concen- 

 trate the folution in fuch a manner, tliat it may form in 

 cooling a mafs, which moulds itfelf in the retort, but of fuch 

 a conmtcncc, that, when placed on its fide, it (liall fuffer a 



II 4 porti<ia 



