[ 175 j J 96 



blue is not to be added from the vat in these colors, except only vvlieii 

 we desire to have a greenish tint. These shades are often liable to be 

 too deep, when they are impregnated with too much alum. In order 

 to avoid this inconvenience, instead of applying the alum like the 

 others, we may make apart for them a weak and small alum bath, in 

 which they may be worked 5 or else, without giving the alum water 

 separately J only a little alum may be put into the same weld-bath. 



To die Blue. 



The following proportions of the articles necessary for a cold blue 

 Tat, were given by an extensive silk dier of Philadelphia.* 



*'One pound of indigo to every pound of copperas: to 120 gallons 

 of water, add 16 pounds of lime, and 6 pounds of indigo." 



Blue. By Mons. RaymondA 



Previously to the year 1811, the silks died blue were dull; but, iu 

 that year, M. Raymond invented a method of giving silk a deep and 

 brilliant color, which is now generally adopted, and is known by his 

 name. Here follows the process. When the silk has been cleansed, 

 immerse it for a quarter of an hour, at the ordinary temperature, in 

 water containing about one-twentieth part of its weight of the sul- 

 phate of the peroxide of iron, J wash, and hold it for half an hour in 

 a bath, nearly boiling, of soap and water; wash it again, and put it 

 in a cold and very weak solution of prussiate of potash, soured by sul- 

 phuric acid, or by muriatic acid. As soon as it is immersed, it be- 

 comes blue, and nothing more is wanting, than, in about a quarter of 

 an hour, to wash and dry it. In this operation, the silk imbibes a 

 certain quantity of feruginous salt; the soap in the water destroys or 

 neutralizes the acid of this salt; the sulphuric acid, or the muriatic 

 acid, unites with the potash of the prussiate of potash, and the prus- 

 sic acid is transferred upon the oxide of iron retained by the silk. 



Silk thus died becomes dull in time, when much exposed to the 

 sun, but will regain its brilliancy by being kept in the dark. 



Chaptal says, in order to obtain the Turkish blue, which is the 

 deepest of all, it is necessary to immerse the silks in a very strong 

 warm bath of savory, before putting it into the vat. 



» The late Mr. John Douga]. 



-f Traite de Chimie, par J. L. Thenard, torn. 4, p. 214. Paris, 1826. 



' According to Thenard, the sulphate of the peroxide of iron is procured in the 

 following' mode: 



<' Expose a solution of green copperas to the air: it then slowly absorbs oxygen, 

 and the sulphate of the peroxide is precipitated in the form of a yellow powder: tlie 

 neutral sulphate of the peroxide remains in the solution, to which it gives a red tinge." 



A manufacturer of Prussian blue, in Philadelphia, procures it in tliis waj': dry cop- 

 neras by exposing it to a heat; then submit it to a more violent heat, until it is con- 

 verted into a grayish red-colored substance, whicli is liie red oxide of iron, combined 

 with a portion of the red sulphate. As it is deliquescent it must be carefully kept 

 from the air until it i? about to be used. 



