FttjicB'tons on PruJJiats, 9 



had a great influence on the tone of thefe fliacles. The fluff, 

 after being dried, was left for fifteen days in a fokuion of 

 prufliat of pot-afli acidulated by the nitric, nmriatic, or ful- 

 phuric acids, and aflumed a pretty equal blue colour, of great 

 beauty and fplendour; but, when deprived of its colour by 

 cauftic pot-alh, it could not be brought back to its fiiTc fliades. 

 The yellow preferving -a decided fuperiority feemed to obfcure 

 the reft; which fliews that the pruffiat of iron had difplaced 

 a great part of the oxvd of fdver; 



The nitric folution of the red oxyd of mercury, with which 

 I impregnated the cotton, in order to dip it in a folution of 

 cauftic pot-afh, gave a very beautiful yellow, while the nitric 

 folution of mercury, newly made, produced a grey; but thefe 

 two ftiades, having been left fonie davs in the folution of the 

 pruffiat of pot-aPn acidulated by the nitric, muriatic, or ful- 

 phuric acids, were changed into blue. The colour being 

 afterwards difcharged by cauftic alkali, the grey and yellcv/ 

 fliades re-appeared — with this difterence, that the latter had a 

 greater refemblance to the ruft of iron. What is fingular is, 

 that the grey differed very little from its firft (hade : if, how- 

 ever, the grey oxyd of mercury had been obfcured by the 

 prufliat of iron, difcharging the colour muft have produced 

 an ochre yellow. 



All thefe experiments prefent phenomena fo fin'gular that 

 they deferve to be repeated; which I fhall perhaps do; but 

 in the mean time it appears to me true that the greater pari 

 of thefe blues arc only prufliat of iron : the changes by affi- 

 nity, however, are extraordinary. It is, above all, on the 

 grey oxyd of mercury changed blue, that it is of importance 

 to fix attention. 



As the precipitates which are formed in mixtures of me- 

 tallic folutions with fokitions of prufliats, of alkalies, or of 

 lime, acidulated, though not blue, are ftill prufliats under 

 different colours, it is very probable that the metallic oxyds, 

 fuch as that of gold fixed on ftuff deftii'ied to bs changed into 

 blue, become prufliats, foluble in acids. In regard to the 

 blue of platina, I have no doubt that it is a pruffiat of that 

 metal ; its change is eifed^ed as fpeedily as that of iron. 



Vol. VI. C III. Account 



