548 VHILOSOPHICAL TRANSACTIONS. [ANNOI768. 



place is in some measure impregnated with iron. When this substance is exposed 

 to the air, it gradually as it dries assumes the blue colour ; the peaty matter in- 

 termixed with it continuing of the same appearance as before. The whole mixed 

 mass is of a very friable texture, easily crumbling between the fingers; and the 

 blue part, gently rubbed between them, feels like a fine impalpable powder. It 

 has hardly any sensible taste; what it has, approaches a little to that of sulphur: 

 the smell, when it is first taken up, is sensibly sulphureous, and if a piece of 

 paper, with part of it adhering to it, be kindled, it shows a flame similar to 

 burning sulphur. 



The only means of separating it from the black matter is by elutriation. 

 When water is poured on it, and they are shaken together, and then left at rest 

 for some time, the black part subsides to the bottom, and the blue can be poured 

 oflT still diffused in the water, from which however it soon separates, and falls to 

 the bottom. It is not possible entirely to free the blue from the peaty matter, 

 for, after above 20 different additions of water, there were still streaks of black 

 interspersed through it, when it was allowed to subside; neither had he ever been 

 able to separate all the blue from any of the black part. When a little water is 

 added to a quantity of it, it acquires some degree of tenacity, and when a small 

 portion of water is allowed to stand on its surface for a day or two, the water 

 becomes of a yellowish colour. 



In order to find whether there was any part of it soluble in water, he passed 

 a large quantity of water, which he had used in separating the black from it, 

 through a filter, and then set it to evaporate in b. m; but there was nothing left 

 in the vessel after the evaporation, except some earth, which the water had probably 

 contained in itself. To a quantity of the blue powder, he added the common 

 vitriolic acid of the shops; a degree of effervescence ensued; and a consider- 

 able froth remained for some time on the surface; the whole was changed 

 into a dark brown colour, and when filtrated, the solution was a trans- 

 parent brown liquor. A considerable sediment remained behind on the filter; 

 but he was inclined to think, that this consisted chiefly of the peaty mat- 

 ter, which had not been entirely separated; for when the experiment was 

 repeated several times with different parcels of the blue, it appeared more or 

 less soluble according as the black had been more or less perfectly separated ; 

 and when he added the vitriolic acid to a quantity of the black, though it 

 turned it all of a brown colour, it only seemed to dissolve a quantity equal to 

 the portion of blue, which still adhered to it. The nitrous acid, added to the 

 blue powder, produced pretty much the same effects, only the filtrated solution 

 was of a much lighter brown. 



The fixed vegetable alkali dissolved also a considerable part of it; but whether 

 the whole or not, he could not say. The solution was an opaque brown liquor. 



