860 PHILOSOPHICAL TRANSACTIONS. [aNNO I768. 



when it is combined with vitriolic acid, in the form of green vitriol, or by itself; 

 and he believed they had no such effect on any, other metal. The colour they 

 produce with it is various, inclining indeed to black, but almost of every different 

 shade between black and blue ; and it seems, that they occasion a more pure 

 black with vitriol, and a purple blue with iron itself, as is seen for instance on 

 dropping a little infusion of tea on a knife. 



Now we find, that when a vegetable astringent is added to a solution of this 

 substance in vitriolic acid, it strikes a black colour with it, and restores the 

 original blue to the white precipitate from that acid. We also find, that there 

 actually is iron contained in it; because, when fluxed with the black flux, its 

 particles are attracted by the loadstone ; and we can draw no argument from our 

 not having discovered iron in the experiment with the blow-pipe, against the 

 presence of that metal, as so little can be examined in that way. He therefore 

 thinks it probable, that the principal ingredients of it, and those on which its 

 colour depends, are iron and some vegetable astringent. The situation in which 

 it is found favours this conjecture very strongly; for, in the first place, the 

 water in the neighbourhood of it is all impregnated with iron; and secondly, 

 in almost every peat-moss, there are the remains of oak trees, still fresh 

 dispersed through them;, .and.ibolh their wood and bark are of a strong 

 astringent nature. \'yi i> ani HpA anHt 



He did not pretend to say, that these are its only ingredients. He thinks 

 we may conclude, from the lightness of the substance, that iron does not form 

 a very great part of it; and the smell, and the jjarticular flame it exhibits in 

 burning, would seem to show the presence of sulphur in it. This, however, 

 can be only in a very small proportion, since so much of it is soluble in acids, 

 which do not at all aflect sulphur. He supposes the precipitate from acids 

 consists chiefly of iron and earth. 



He had made some trials on the blue powder after it was partly well freed 

 from the black matter, in order to see how far it might be useful as a paint: a 

 quantity of it was rubbed in a glass mortar with oil of walnuts; but, after being 

 thoroughly mixed with the oil, its colour was changed to black. It is probable, 

 therefore, that little can be expected from it as an oil colour; but it retains its 

 natural brightness when mixed with gum-water; and, as it is naturally in a 

 very fine powder, it is diffused intimately through it without any difliculty, so 

 that, if it could be got in sufficient quantity, it would be a cheap and useful 

 water-colour. He thinks there is reason to believe, that it might be found 

 in most peat-mosses, as what seem to be materials of which it is composed are 

 present almost in all of them. Two or 3 years ago a gentleman sent him a 

 parcel of it, which he found in a moss on his estate, 5 or 6 miles distant from 

 the place where he first observed it. He was informed, that Mr. Da Costa had 



