INKS. 143 



bichromate of potassa and an acid, but is objectionable because 

 the white ground requires cleaning. Mercer (Phil. Mag.) pro- 

 poses to effect it by red prussiate of potash and caustic alkali ; 

 for when the former is printed on, and the cloth is then passed 

 through dilute caustic-lje, a brilliant white is discharged. 



Ammonia-oxide of Copper. — Runge draws attention to the 

 resolution of sulphate of copper in ammonia (Polytech. No- 

 tizbl. 1847), and shows its utility for color-printing, when 

 mixed with decoctions of plants. Thus, catechu gives almost 

 the same brown as chromate of potassa, by fusing 1 pt. ca- 

 techu in 4 pts. water, adding 12 pts. of the liquid ammonia- 

 oxide of copper, and printing with the liquid, thickened with 

 tragacanth. It shows a singular action on the yellow color 

 which separates from a cold infusion of French berries. This 

 color, when treated with the ammoniacal copper, becomes 

 reddish-brown in the course of 6-8 hours, and if then treated 

 with alcohol, the brown copper-salt is left, and a red color 

 dissolved, which yields compounds with alumina of a beautiful 

 red, like those from madder. 



Pyroplios'pliaie of Copper and Potassa. — Persoz proposes 

 this double salt for calico-printing, as it is decomposed by zinc 

 or iron with less facility than any other salt of copper, and 

 as difficulties attend the use of other salts of copper. (Ann. de 

 Chim. et de Phys. and Journ. f. Prac. Chem. xli. 361.) 



7. Coloring Fluids. — We may conveniently embrace under 

 this head various fluid inks, which are liquid dyes ; as well 

 printing-inks, which are pasty dyes, printed on from a type 

 or pattern. 



Black Ink from Logtvood. — Boil 125 pts. rasped logwood 

 with so much water that it will yield 1000 pts. of the decoc- 

 tion, and when cold, stir in 1 pt. yellow chromate of potassa. 

 It is a beautiful blue-black, and gives no precipitate. But if too 

 much chromate be used, or the decoction be too concentrated, 

 a dark precipitate takes place. (Runge's Grundriss d. Chem. 

 ii. 207, 1847.) Being free from acid, it will not corrode steel 

 pens, but it does not write as freely as our most fluid inks, 

 made from nut-galls and copperas. 



