1000 



and cceteris paribus, the rapidity of elimination, and the richness of 

 colour ultimately produced, stand in a direct ratio to the degree of 

 temperature, but that, above this point, the same ratio immediately 

 declines. The most rapid evolution, however, appears to be incon- 

 sistent with the production of the richest and most permanent tints ; 

 for I generally found that the colours most speedily produced by a 

 pretty high temperature, and excess of alkalies, faded most rapidly. 

 I have therefore been more successful in obtaining fine colours by 

 macerating in closed vials, in cool places, with common spring water, 

 and a moderate quantity of alkali, than when I endeavoured (prema- 

 turely, as it were) to force on development by an opposite combination 

 of circumstances. In former days, the ammonia was wholly supplied 

 in the form of stale, or putrid, urine, which was gradually added to 

 the powdered lichen ; the mixtme frequently stirred, fully exposed to 

 the air, and set aside, to ferment, in a moderately warm locality ; when 

 a sufficient depth of colour and a proper consistence were attained, the 

 mass was dried, after having been made up in the form of balls, cakes, 

 or lumps ; or it was preserved for use in the state of powder. Urine, 

 as a decomposing agent, gradually gave place to different kinds of 

 ammoniacal liquids, obtained by the distillation of decaying animal 

 matters ; and, at the present day, the manufacturers of orchil, cud- 

 bear, and litmus, generally use either tolerably pure dilute liquor 

 ammoniae, or the ammonial liquor of gas-works. Maceration in stale 

 urine, however, is not only still had recourse to in many remote parts 

 of our highlands and islands, by the old women, for preparing dye- 

 stuffs from various kinds of ' corkir,'* but is largely employed in the 

 manufactories of some of the most extensive orchil and cudbear- 

 makers in England. Manufacturers find, what we should a priori 

 expect, that its value as a metamorphosing agent is directly in pro- 

 portion to the amount of urea it contains. When, therefore, it is very 

 deficient in this substance, it is comparatively useless, and is conse- 

 quently rejected. This is evidently due to the small amount of car- 

 bonate of ammonia generated by the decomposition of the diminished 

 portion of the urea. Mr. Reynolds, of London, informs me that a 

 large orchil and cudbear-manufactory in Leeds, which is in the con- 

 stant habit of using large quantities of stale urine, collecting it from 

 the neighbourhood, ' find that, when collected from beer-shops, it is 

 utterly worthless, and they refuse it accordingly.' As thus employed, 

 urine has generally been looked upon merely as a cheap and easily 



" * The vernacular generic term for lichens capable of yielding colouring matters." 



