8 Rtjteiilons on FruffiaU, 



blues arofe only from iron, which the foliitions of prufliats of 

 pot-afli and of lime hold more or Icfs in folution. I learned 

 alfo, from a paflTage in EufTon in his obfervations on the na- 

 ture of platina, that Morveau had doubted the experiment of 

 Fourci, who precipitated gold of a blue colour by the pniflian 

 alkali. Though we cannot deny the exiftence of iron in pruf- 

 fiats of alkalies and of lime, I could^ however, with difficulty 

 believe that a metallic fubftance fixed on ftuff, could be re- 

 placed by any other which would at the fame time remain 

 fixed. 



If, in my experiment on cloth coloured by the oxyd of 

 gold, that oxyd had difappeared ; if the prufliat of iron had 

 been precipitated in the liquor, inftead of being fixed on the 

 fluff; iftheafliesof fome fpecimens had not gilded filvcr; 

 and, in the lad place, if the intenfity of blues had not been fo 

 confiderable and fo general, and the fliadcs of each different, 

 I {hould certainly have been fooner freed from my error; but 

 I now am, and the following is the method in which I pro- 

 ceeded to convince myfelf of my m i flake : — I deprived of its 

 colour, by means of a folution of pot-afli, a piece of cotton 

 cloth coloured yellow by gold, and then rendered blue : I 

 waflied it, and immerfed it for feveral hours in a muriatic 

 folution of tin, and produced the lame efledl as with the oxyd 

 of iron. This cloth, deprived of its colour, and become of a 

 yellow fimilar to that produced by the oxyd of iron, was 

 changed into blue by alkaline prufliats as fpeedily as the 

 latter. This blue cloth, as well as that deprived of its co- 

 lour by pot-afli when reduced to afhes, fcarcely gilded filver; 

 and thefe aflies, treated with mercury, furniihed only a flight 

 gilding, arifing no doubt from a fmall portion of the oxvd 

 of gold which had remained untouched in the liquor of the 

 acidulated prufTiats, which, by longer immerfion of the ftufF, 

 could not have failed to have been taken up. 



Thefe proofs were too ftriking not to induce me to con- 

 tinue my experiments. I foaked, therefore, the cotton cloth 

 in a nitric folution of filver, and, without drying it, I dipped 

 it in a folution of cauflic pot-afh ; the oxyd fixed on the fluff 

 prefentcd inequalities, and exhibited different ihades of vio- 

 let, lilac, grey, and yellow. The a<Stion of the almofphere 

 7 had 



