INDIGO-BROWN 



913 



obtain upon wool bright blue bottoms such as were formerly producible only by means 

 of the sulphate of indigo, and which were, of course, much more fugitive. 



In printing with indigo, the process hitherto followed lias been to use white indigo, 

 or indigotate of tin obtained by precipitating a tin vat with hydrochloric acid or by 

 adding to the clear portion of a copperas vat a mixture of hydrochloric acid and salt 

 of tin. This precipitate is thickened with gum, and printed upon the calico. It is 

 then fixed by treatment with milk of lime. The goods are then successively passed 

 through bl caching-liquor, sulphuric acid, and a soap-bath. The process is at once 

 difficult, delicate, and expensive. It is only by constant and anxious attention that 

 running and injuries to the accuracy of the design are avoided during the treatment 

 witli lime-water, and only a very small fraction of the indigo is actually deposited 

 upon the fibre. The numerous attempts hitherto made to replace the above-described 

 process with some other means of fixing indigo have not proved successful. We need 

 only mention as instances, China blue, pencil blue, and printing with a concentrated 

 indigo-vat in an atmosphere of coal-gas in order to exclude atmospheric oxygen. The 

 new method, as tested by the authors upon a manufacturing scale, consists mainly in 

 printing with an alkaline solution of dissolved indigo suitably concentrated and 

 thickened, the colour containing, moreover, a large excess of hydrosulphite of soda. 

 The presence of this salt keeps the indigo-blue constantly in a perfectly-reduced state, 

 which would otherwise become oxidised. It thus supersedes in a much more con- 

 venient manner the use of coal-gas. The printing can be carried on in common air 

 with ordinary machines. Oxidation is so little perceived that after an hour of working 

 the colour remains reduced to yellow. On the other hand, by printing on dissolved 

 indigo, immediate fixation is secured as the colouring matter is almost entirely 

 utilised. Experience shows that with shades of equal depth, solid blues are obtained 

 at an expenditure of from 50 to 60 per cent, less indigo than with the old process. 

 The shades obtained are more beautiful and solid, and the design comes out more dis- 

 tinct and better defined. The new blue not needing to be fixed by any subsequent 

 process after printing, can be applied simultaneously with the majority of other colours, 

 such as aniline-black, garancine colours, whether obtained by dyeing or steaming, 

 catechu, chrome colours, albumen colours, &c. Novel styles can be thus originated, 

 which could scarcely be executed by any other process. The new colour is obtained 

 by thickening with gum, or any other suitable substance, an alkaline solution of white 

 indigo sufficiently concentrated, and adding to the mixture a sufficient quantity of 

 hydrosulphite of soda. After printing, the indigo is oxidised by hanging up the pieces 

 for twelve to fourteen hours. They are finally washed and soaped. 



Our Imports of indigo in 1871 and 1872 were as follows : 



XWDXGO-BJtOWW. A brown substance of uncertain composition obtained from 

 commercial indigo. 

 VOL. II. 3 N 



