ON PLUMBAGO 



179 



former. (c) The same process was repeated with eight 

 parts of nitre, and here a little plumbago remained which 

 was not calcined by the nitre. All the masses remaining 

 in the crucible were dissolved in water, when a good deal 

 of undecomposed plumbago fell to the bottom. The limpid 

 solution neither contains hepar nor vitriolic acid ; conse- 

 quently there is no sulphur in pure plumbago, (d) At last 

 I mixed one part of levigated plumbago with ten parts 

 of nitre, and put it into a red hot crucible ; a detonation 

 followed, and after it was kept for a few minutes in a state 

 of fusion, a white alkaline mass appeared, which I poured 

 out upon a copper plate, and afterwards dissolved it in 

 water, upon which a little brown powder was precipitated. 

 From 1 oz. of plumbago thus calcined with nitre, I obtained 

 15 grs. of this brown powder, which I found to be ochre 

 of iron. Upon pouring some vitriolic acid into the alkaline 

 solution, an effervescence ensued, and the air expelled was 

 aerial acid mixed with nitrous air (acidum nitri phlogisticatum), 

 and the whole mixture became gelatinous. I filtered the 

 whole together, and found that what remained in the filter 

 was siliceous earth mixed with a little earth of alum. The 

 saturated solution yielded, after evaporation, nothing but 

 vitriolated vegetable alkali, (e) But not being convinced 

 by this experiment of the existence of clay in plumbago 

 for I have elsewhere more particularly shown (Dissertation 

 on Silex, Clay, and Alum) how unsafe all experiments of this 

 kind are in common crucibles I made the same detonation 

 with plumbago and nitre in an iron crucible, and found that 

 I was right in my suspicion, for not the least mark of clay 

 was now to be discovered. 



