31 8 On the Colouring Vrlnclph of Lapis Lazuli. 



iron be tinrred blue without a combination either with the 

 pruflic or the phofphoric acid ? Mr. Klaproth fays that he 

 does not know *. 



The experiments of which I am about to give an account 

 fecm to me to afford a fohition of this important quefilon : 

 but before I prefent the proceffes and the refuUs, I ought, 

 for the fake of perfpicuity, to give an account of fomc la- 

 IxHirs, which paved the way for arriving at this conclufion. 

 In the vcar 1780, when infpefting a pit in fcarch of coal at 

 Montolier, in the road from Dole to Poligny, I found, at the 

 tiepth of 35 metres, a gypfeous bed containing zones of a 

 beautiful very bright red colour. I gave a defcription and 

 analyfis of it in the Journal dc Phyjique for the month of 

 December that year, and I concluded from mv experiments 

 that it was fulphat of lime coloured by the oxyd of iron. 



The recent difcovery of feveral new metallic fubllances, 

 lome of v.hich had the property of giving colours of great 

 intenfitv, induced me to think that the foffil of Montolier 

 deferved to be again examined with a view of fearching for 

 one of thefe oxyds. For this purpofe, at the commencement 

 of this year, I deftined a piece of it for the experiments in 

 the analyfes of minerals, which form part of my courfe at 

 the Polytechnic School. They were conduced with as much 

 preciilon as fagacity by C. Deformes, formerly a pupil in the 

 laboratory of the fecond divifion. Having afcertained that this 

 foffil contained no carbonat of lime, we took ten grammes 

 of it, reduced to powder, which was put in a crucible and 

 brotight to a red heat. The colour became darker, and 

 pafl'ed to a vellowifli-brown, and there was a lofs in the 

 weight of 2*23 grammes, or 22 "3 per cent. 



A. We digv fted, at feveral times, the muriatic acid on 

 the 7'77 that remained after calcination; they did not lofe 

 their colour, and the acid took up only a very fmall portion 

 of the iron. 



B. We afterwards boiled the refiduum in a folution of the 

 carbonat of pot- a(h, but only a very fmall part was decom- 

 pofed . 



C. What remained was mixed with charcoal dull, and 



* Sec his Bejtra^f, &x. Vol. I. p. 201. 



7 treatcii 



