BIS′TRE

(-ter). [Eng., Fr.] Syn. Bister , Ger. Prep. 1. The most compact, best coloured, and well-burnt portions of the soot of beechwood, or of peat, [184] are selected, reduced to powder and sifted through a very fine lawn sieve. It is then digested in clear warm water for several hours, with frequent stirring; after which it is allowed to settle, when the liquid portion is decanted from the sediment. This proce is repeated a second, and even a third time. The paste is next poured into a tall narrow ve el, which is then filled with pure cold water, and well agitated. The gro er parts only are now allowed to subside, [185] and the supernatant liquor, containing the finer portion of the BISTRE in suspension, is poured off into another ve el, where it is left to deposit its contents. The deposit is next collected, and carefully dried and powdered; or it is only partially dried, and at once made into cakes with gum-water or isingla -size, and then allowed to dry and harden for sale. [184] The first is usually employed in England. [185] Two or three minutes suffice for this purpose. 2. (Dr MacCulloch.) The tar-like liquid obtained from the dry distillation of wood is again carefully distilled until all volatile matter has pa ed over, and a brittle, pitch-like residuum is obtained, which is either brown or black according to the time and temperature employed; after which the heat is still further prolonged, but with increased care, until the brittle substance becomes pulverulent and carbonaceous. It is then ground and elutriated with pure cold water, as before. Uses, . As a water colour to tint drawings, in the same way as Indian ink, to which it is esteemed superior when the subjects are intended to be afterwards tinted with other colours. It occupies the same place among water colours that brown-pink does in oil. According to Dr MacCulloch, bistre from wood-tar, when carefully prepared, has great depth and beauty of colour, with all the fine properties of sepia; but that if the whole of the oils and acids have not been removed by the proce , it is apt to collect in little flocks which interfere with its use.