ON PLUMBAGO 183 



usual; and when one part of this kind of plumbago was 

 detonated with six parts of nitre, I have found some hepar 

 at last. When therefore plumbago, during calcination, yields 

 a sulphureous smell, it must be mixed with a little pyrites. 

 That pure plumbago does not enter into any union with 

 sulphur, appears from Sec. n. (c) ; and that it contains no 

 sulphur, appears from Sec. I. ; for if this were the case, I 

 should have certainly obtained in the neck of the retort 

 either a red or a yellow sublimate. See likewise Sec. in. (c). 



If cast-iron be dissolved in diluted vitriolic acid, a black 

 mass remains, which is insoluble in acids, and which has 

 been supposed to be plumbago. I shall therefore take 

 this opportunity to relate the experiments I made with 

 this residuum. I extracted 1 oz. of it by means of aqua 

 regia, which thereby acquired a dark yellow colour. After 

 having decanted the solution, I poured some new menstruum 

 upon the residuum, and continued in the same manner, till 

 there appeared no more iron in the menstruum. I dried 

 the residuum, and found that it had a shining black colour, 

 and between the fingers it felt like plumbago. It now 

 weighed no more than 3J drms. Mr. P. J. Hjelm, having 

 roasted this residuum under . the muffle, found that it 

 calcined somewhat more quickly than plumbago. The 

 remainder of this calcination was a very Small quantity of 

 white ashes. 



One part of the above-mentioned residuum of cast-iron 

 was mixed with five parts of nitre, and put into a red hot 

 crucible ; a detonation followed, as with plumbago ; the 

 alkaline mass remaining in the crucible, which was of a 

 white colour, I dissolved in water, whence after some time 

 a little white sediment precipitated, which however was not 

 sufficient for making any decisive experiment. The solution 

 or lixivium effervesced with acids, and showed the same 



