272 VEGETABLE SUBSTANCES. 



other salts are found mixed with it in small propor- 

 tions. These are usually the sulphates and the 

 muriates of potash and of lime, besides which a 

 portion of earthy matter is likewise held in com- 

 bination. 



Kirwan furnishes the following directions for 

 making potash from weeds. The weeds are cut just 

 before seeding time, spread out, and when sufficiently 

 dry, collected free from all extraneous matter. They 

 are then burnt within doors on a grate. The ashes 

 are gathered together as fast as they are produced, 

 and any pieces of charcoal which may be found 

 mixed up with them are rejected and again subjected 

 to the action of the fire. This should be clear and 

 brisk, a close smothered fire, though recommended 

 by some, being prejudicial to the production of ;ood 

 ashes. The ashes when thus obtained are mixed 

 with twelve times their weight of boiling water 

 This hot water holds in solution the alkali, while the 

 grosser and insoluble particles of the ashes subside ; 

 the supernatant liquor is then filtered off and evapo- 

 rated to dryness in iron pans. Two or three vessels 

 are used in the business, and when the evaporation 

 has been continued until the lessened solution is 

 more than saturated, as fast as the salt concretes it 

 is passed from one pan to the other : thus time is 

 saved as the water evaporates more quickly when 

 less surcharged with the alkali. It is said that 

 potash was so designated from the circumstance of 

 its being prepared in pots. 



The salt thus produced is of a dark colour, in con- 

 sequence of its containing much extractive matter. 

 To get rid of this another operation is required. The 

 potash is placed in a reverberatory furnace, in which 

 the extractive matter is burnt off, and much of the 

 water is dissipated, It generally loses in the furnace 

 from ten to fifteen per cent, in weight, but it gains 



