WELD. 381 



posed fast colour was given by the combination of 

 weld with a certain mordant, the composition of 

 which the patentee was permitted to conceal, that 

 foreigners might not enjoy the benefit of his disco- 

 very ; while he, on his part, engaged to supply the 

 cotton and thread dyers with his dye at a certain 

 fixed price. The mordant used was supposed by 

 chemists to be a solution of tin alone, or of tin and 

 bismuth, which gives to weld yellow the power of 

 resisting the action of acids and of boiling soap-suds, 

 though it is not proof against the continued action of 

 the sun and air. This defect, however, was not 

 easily discoverable, in consequence of the ingenious 

 method which, according to Dr. Bancroft, the in- 

 ventor employed to obtain a favourable testimony of 

 the dyers on the subject. He caused his specimens 

 of dyed yarn to be woven into pocket-handkerchiefs, 

 and gave them to be worn in the pockets of those 

 who were afterwards to attest to the goodness of his 

 dye ; and as handkerchiefs enclosed in pockets are 

 not exposed to the sun and air, this want of perma- 

 nency of colour was not discovered until some time 

 after the reward had been paid, for an invention 

 which proved of little or no value. 



A water-colour, called weld yellow, is much used 

 in paper-hanging manufactories. This pigment, as 

 it is usually prepared in London for sale, is the ex- 

 tract of the plant, and is in the form of hard lumps, 

 which must be ground into powder previously to 

 being used. Every colour is in some degree injured 

 by that operation. Messrs. Collard and Eraser, 

 therefore, use a process by which the necessity for 

 subsequent grinding is avoided, the colour being 

 obtained in the form of a fine powder. To produce 

 this desirable result equal quantities in weight of 

 carbonate of lime and soft water are put into a cop- 

 per vessel ; the mixture is raised to the boiling point, 



