VOL. LVIII.] PHILOSOPHICAL TRANSACTIONS. 549 



which did not become transparent after being twice filtrated, though it deposited 

 no sediment upon standing several days. He added a small quantity of volatile 

 alkali to it, which seemed to dissolve part of it, and turned the rest obscurely 

 green. To the solution in vitriolic acid, he joined some fixed vegetable alkali: 

 an effervescence arose, and a light curd of a colour between green and blue 

 was thrown to the top, which soon subsided, and became white. A similar 

 precipitate was obtained from the nitrous acid, only it was not at first thrown 

 up to the surface in the same manner as the foregoing. 



From the solution in fixed vegetable alkali, a reddish brown precipitate was 

 obtained, by the addition of vitriolic acid. Equal quantities of the blue powder and 

 of black flux were mixed together, and being put into a crucible, were kept in a 

 a strong degree of heat for several hours: on being removed, and taken out of 

 the crucible, the whole was found concreted into a spongy mass, the bottom of 

 which was crusted over With something that had a kind of metallic appearance. 

 This mass was powdered, and the lighter parts washed off; after which a magnet was 

 applied to what remained, and it attracted many of its particles strongly, without 

 being brought in contact with them. 



Part of the white precipitate from vitriolic acid was mixed with a little fixed 

 alkali, and being laid on a piece of charcoal, the flame of a candle was directed 

 to it by means of a blow-pipe. It was thus kept in a red heat for about an 

 hour, and on being removed, the magnet was applied to it, but none of the 

 powder was attracted by it. The quantity that can be examined in this way does 

 not exceed a few grains. 



To a small quantity of the white precipitate, he added an infusion of tea; 

 which turned it blue, approaching to the original colour, but not so deep. To 

 another parcel of the same, he added some infusion of galls, and shook them 

 together. The liquor became of a dark blue colour, and what part of the 

 powder remained at the bottom of the glass was of the same colour. This was 

 not so bright as that of the original powder diffused in water, but entirely such 

 as might be expected from the diffusion of it in a brown liquor like infusion of 

 galls; and, to show this, he poured some of the infusion of that astringent on 

 the blue substance itself, and on shaking them together, they produced a 

 colour almost entirely the same. A quantity of the brown solution in vitriolic 

 acid was diluted with water till it became very pale. He then poured to it some 

 infusion of galls, which turned it immediately black. A parcel of the blue 

 substance, being placed at the distance of a foot from the fire, was changed to 

 a greenish colour. 



These experiments, compared with its natural history, seem to throw some 

 light on the nature and composition of this curious production. It is the 

 known property of all vegetable astringents, to affect the colour of iron, either 



