MORDANTS. 131 



■where the alkaline base is absent, the decomposition by oxida- 

 tion is more violent : a fact of importance in the use of this 

 bleaching agent. 



Bristles Bleached. — Winkler and Fink give the following 

 as the best method of bleaching bristles. (Mona*sbl. d. Hess- 

 isch. Gewerbver. 1847.) They are first well washed in a 

 solution of soft-soap in luke-warm water, rinsed in cold water, 

 then laid for 2-3 days in a saturated solution of sulphurous 

 acid in water, well washed, and dried. By merely moistening 

 and exposing them to the air, most kinds may be bleached, 

 and still better by moistening them with very dilute sulphuric 

 acid, and sunning them. In the latter case, however, Winkler 

 observed that they were slightly attacked by the acid. 



3. 31ordants. — Under Chemics, we have seen the preparation 

 of the two great mordants, alum and copperas, together with 

 several others. A few are prepared more exclusively for the 

 dyer, and some by the dyer himself. 



Persulphate of Iron. — A mixture of powdered copperas and 

 some soda-saltpeter is ignited for a short time in a crucible, 

 and, when cooled, extracted by water. The presence of the 

 sulphate of soda, also formed by the process, does not inter-i 

 fere with its employment in dyeing, &c. Eisner properly 

 remarks that this process is not as economical as the older 

 method of heating a due mixture of oxide of iron and oil of 

 vitriol in a cast-iron vessel. It may nevertheless be sometimes 

 convenient to employ it. (Mechan. Mag. 1847.) 



A good article on the nitrates of iron, &c., appears in the 

 American Journal, 2d series, ix. 30, by Ordway. 



Nitrate of Copper. — This salt may be made by mixing 1^ 

 pts. powdered blue vitriol with 1 pt. soda-saltpeter, moistening 

 it with water, and heating it in a crucible until the fluid mass 

 begins to evolve red vapors. The solution then made will 

 contain sulphate of soda, which does not injure its value to 

 the dyer. (Mechan. Mag. 1847.) 



Tin-salt. — C. Nollner proposes (Ann. der Chem. u. Pharra. 

 Ixiii. 120) to adapt stoneware receivers to the retorts m which 

 muriatic acid is generated, and to fill them with granulated 



