382 VEGETABLE SUBSTANCES. 



and stirred until it becomes of a uniform consis- 

 tence. Then, to each pound of carbonate of lime, 

 three ounces of pulverized alum are added ; this ig 

 gradually mixed in, and as carbonic acid gas is by 

 this means disengaged, the operation must be care- 

 fully performed, lest the effervescence which takes 

 place should cause the mixture to overflow from the 

 boiler. When the effervescence has subsided this 

 part of the process is completed, the fire is with- 

 drawn, and the mixture may remain any length of 

 time without injury. Meanwhile the weld plants are 

 placed with their roots uppermost in another copper 

 vessel, into which soft water is poured in just suf- 

 ficient quantity to cover every part containing seed. 

 These plants, after being boiled for a quarter of an 

 hour, are removed to a tub, where they remain until 

 the liquor is drained from them ; the water in which 

 they have been boiled, added to these drainings, are 

 then passed through a flannel filter, to intercept the 

 seeds and fecula. The quantity of plants required 

 for a given quantity of carbonate, of lime cannot pos- 

 sibly be ascertained with accuracy, for some bundles 

 contain three times as much colouring matter as 

 others ; but should too much of either mixture have 

 been prepared, it can be kept in earthen vessels for 

 many weeks without being in any way deteriorated. 

 When the weld liquor has been thus prepared, a 

 fire is again kindled under the boiler containing the 

 basis to which the weld liquor is added. The proper 

 degree of colour required can only be obtained by 

 trial. When the mixture is found to have a due pro- 

 portion of each, it is raised to a boiling heat and 

 the process is completed. The contents of the 

 vessel are then put into an earthen receptacle, and 

 the colour precipitates in the form of a powder. The 

 next day the supernatant liquor is drawn off, and the 

 residuum placed on large pieces of chalk, which in a 



