'$to ' On the Nature of the colouring Piinciple of the Lapis-lazuli. 



D. The liquids of the three preceding operations were put together, and then divided 

 into two equal portions. From the firft the iron was feparated, and was found to weigh 

 10.5, and it was afccrtained that it contained no other earth except lime. Fronx the 

 fecond, eight decigrammes or hundredth parts of lime, were obtained. 



The whole of the folution, therefore, contained : 



Oxide of iron - - 21. 



Lime - - - 16. 



Sulphuric acid - - 29.1 



the laft according to the proportions determined by Klaproth. 



E. It remained to examine the portion of earth left by the acid, and which was mixed 

 with the fuperfluous coal. It is here that the operations began to prefent unexpected 

 phenomena, and which, by deviating from the ufual courfe, advife the attentive chemift 

 that he is on the eve of difcovery. 



This refidue was at firft calcined in the open air, in order to burn the coal, but the 

 filiceous earth remained black : its weight was 16.5. 



It was treated with potafli in a crucible of platina, and yielded a fufible mafs of a 

 fuperb blue colour. 



Water poured upon it aflumed the fame colour. 



Nitric acid made it totally difappear. 



The filiceous earth feparated by evaporation to drynefs weighed only 8.6. 



F. It became of confequence to know the efFedl of the different re-agents on the acid 

 which had been applied to the mafs fufed in the crucible, which might difcover the fub- 

 ftance which afibrded its properties. The following is the refult of thefe trials : 



1. With prufllate of pot-afii this fluid yielded a precipitate of a yellowifh green colour, 

 which the addition of acids caufed inftantly to difappear inftead of reviving the blue. 



2. With the gallic acid there was no precipitate. 



3. With fulphurated hydrogen there was no precipitate. This, indeed, was to be ex- 

 pefted upon the fuppofition that iron alone was prefent, but it was proper in this manner 

 to exclude the other metallic fubftances which are precipitated by this re-agent. 



4. With hydro- fulphuret of ammoniac there was a fine green precipitate. 



5. With ammoniac there was a white precipitate- 



6. With pot-a(h there was a light blue precipitate. 



The two laft colours changed, in the drying, to a yellow. 



Some comparative experiments were made at the fame time with a folution of nitrate of 

 iron, and the refult of them was totally different. 



G. That there might remain no doubt refpedting the nature of the fubftances by whofe 

 prefence the refults of thefe operations was afFefled ; fynthefis was called in to the 

 affiftance of analyfis. Sulphuret of iron was prepared in the direcl way; a fufiicient 

 quantity of nitrous acid was poured upon it ; the filtered liquid was diluted with much 

 water, in order that the excefs of acid might no longer precipitate the fulphurated hydrogen 



which 



