214 The Art of Dyeing. 



be employed in printing, as they do not combine with the 

 stuff like the acetates, but are washed away again by the 

 process of rinsing. 



Nitric acid. — This acid which also occurs in commerce, 

 under the name of aquafortis, is of little use for the cotton 

 manufacture. It is employed very seldom, and usually in 

 such cases (nitrate of lead excepted) another acid would 

 answer equally well ; for example, nitrate of zinc, nitrate 

 of iron, and nitrate of copper. 



The two last answer as an addition in dark calico-print- 

 ing, and their exhibition requires some caution. 



When nitric acid of the usual strength is poured upon 

 iron filings, red fumes are disengaged, the liquid boils, and, 

 when the vessel is not very high, the whole passes over. 

 What remains is a thick brownish red mass, which is quite 

 useless. In this way nitrate of iron can be prepared. The 

 mode of proceeding should be reversed, viz. instead of pour- 

 ing the acid upon the iron, by introducing gradually some 

 iron into the acid, and this is not to be repeated until all 

 the iron previously added be dissolved. In this way the 

 heat may be increased, although, by placing the vessel in 

 cold water, the process is more securely performed. Good 

 nitrate of iron should be dark-brown, and quite clear. Nitrate 

 of copper and nitrate of zinc should be prepared with the 

 same precaution. On a large scale it is more profitable, 

 instead of copper and zinc, to dissolve copper chips and 

 flowers of zinc in the nitric acid. 



Of all the acids, nitric acid acts most injuriously on cot- 

 ton ; it should, therefore, be added in very small quantity 

 to caustic mordants, and where it is possible its use should 

 be dispensed with. 



Acetic acid. — Strong acetic acid acts under no circum- 

 stances disadvantageously upon cotton fabric. Therefore, 

 all metallic solutions, (mordants) when it can be done, are 

 employed in the state of acetates. The acetate solutions 

 are obtained partly by dissolving the metals directly in 

 vinegar, as for example iron. This is allowed to get rusty 

 in the air, and is then digested with vinegar. Since the 

 efficient part of pyroligneous acid is also acetic acid, it may 

 be employed for the same purpose instead of vinegar. This 

 kind of solution, however, requires a long time. 



