DYEING. 



that intended in this bath, afterwards dip- 

 ping it in the archil bath, and lastly in the 

 blue vat. 



When raw silk is to be dyed blue, that 

 which is of a white colour should be cho- 

 sen. It should be thoroughly soaked in 

 water, and afterwards put into the vat in 

 separate hanks, in the same manner as 

 the scoured silk. In general, raw silk 

 takes the dye more readily ; wherefore, 

 when it can be done, the scoured silk is 

 put into the bath before it. If raw silk 

 requires archil, or the other grounds 

 mentioned, it should be treated as direct- 

 ed for silk in general. 



The solution of indigo in sulphuric acid 

 is also used for silk ; the colour called 

 English blue is produced by it. To give 

 silk this colour, it is first dyed a light 

 blue, and then dipped in hot water, wash- 

 ed in a stream, and afterwards left in a 

 bath made with the sulphate of indigo, to 

 which a little tin has been added, till the 

 proper shade is obtained, or the bath ex- 

 hausted. 



The silk, before it is put into this bath, 

 may be dipped in a solution of alum, in 

 which it should remain only a very short 

 time. Silk, dyed in this manner, is free 

 from the reddish shade given by the blue 

 vat, and from the greenish cast of com- 

 mon Saxon blue. 



Of dyeing Cotton and Linen blue. 



The vat for dyeing cotton and linen 

 blue should contain, according to M. 

 Pileur d'Apligny, about 120 gallons. The 

 quantity of indigo used is generally from 

 six to eight pounds. This indigo, after 

 being pounded, is boiled in a ley drawn 

 off clear from a quantity of lime equal to 

 the indigo, and double its weight of pot- 

 ash. The boiling is continued till the 

 indigo is thoroughly penetrated with ley, 

 which should be carefully stirred all the 

 while. 



During the boiling of the indigo, an 

 equal weight to it of quicklime is to be 

 slacked; about twenty quarts of warm 

 water are added, and in this is dissolved 

 sulphate of iron, twice the weight of the 

 lime. When the solution is completed, 

 the liquor is poured into the vat previous- 

 ly half filled with water. To this the so- 

 lution of indigo is added, and the rest of 

 the ley not used in boiling it. After this 

 the vat must be filled up to within two or 

 three inches of the brim, and be raked 

 two or three times a day, till it is fit for 

 dyeing ; which generally happens in 48 

 hours, or sooner, according to the tem- 



persture of the air. Some add to this vat 

 a little bran, madder, and woad. 



In the process used at Rouen, which is 

 simpler, 20 pounds of indigo, macerated 

 for a week in caustic ley, which will float 

 an egg, are ground in a mill ; three hogs- 

 heads and an half of water are then put 

 into the vat, and afterwards twenty 

 pounds of lime. When the lime is 

 thoroughly slacked, the vat is raked, and 

 thirty-six pounds of copperas are put in. 

 When the solution of this is complete, the 

 ground indigo is put in through a sieve. 

 On the same day it is raked seven or eight 

 times ; and after having stood 36 hours it 

 is fit for dyeing. 



Bergman recommends a still simpler 

 bath, composed in the proportions of 

 three drachms of powdered indigo, three 

 drachms of copperas, and three drachms 

 of lime, to two pints of water. This being 

 well raked will, in the course of a few 

 hours, be fit for use. 



The solution of indigo in sulphuric 

 acid has been hitherto only used for 

 dyeing wool and silk. The affinity of ve- 

 getable substances for indigo is not suffi- 

 ciently strong to separate it from the 

 sulphuric acid. It cannot therefore be 

 employed to advantage in dyeing cotton 

 or linen. 



Attempts have been made to dye cloth 

 with Prussian blue, but no method has yet 

 been found to make this colour apply it- 

 self evenly, sufficiently certain and per- 

 fect for general use. This process de- 

 serves farther experiments, as the colour 

 produced by it was very beautiful, and 

 not liable to change, though exposed to 

 all the vicissitudes of the air. But dust 

 and rubbing injure it ; and any touch of 

 an alkaline liquor destroys it altogether. 

 The process in which stuffs, previously 

 impregnated with alum and copperas, 

 are submitted to a solution of Prussian al- 

 kali, seems that most likely to succeed 

 in diffusing the dye equally, if improved 

 by farther trials. Perhaps also a solution 

 of caustic alkali might form a sufficient 

 solvent for the Prussian blue, if ground 

 with it, to admit of its being used in some- 

 what the same way as indigo. 



Of dyeing Wool red. 



Red colours are of various shades, ac- 

 cording to the nature of the colouring 

 matters used. They all require mor- 

 dants to render them permanent. The 

 principal shades of red are, scarlet, crim- 

 son, and madder red. 



Madder red is only employed for dye- 



