MINERAL DYES. 399 



same dye. Substitute four pounds of green vitriol for 

 the alum used in. the previous case, and the madder 

 gives a deep black. Add four ounces of arsenic with 

 the green vitriol, and a mordant is produced with which 

 the dye will yield a beautiful purple. In the latter 

 case, the solution must be reduced to one-tenth of its 

 original strength by the addition of water. 



1000. DYEING WITH LOGWOOD. By the 

 briefly the pro- employment of the last two mordants, 

 with lo d wood 9 ? m i xe d m equal proportions and diluted with 

 an equal quantity of water, a mordant for 

 dyeing black with logwood is obtained. For dyeing 

 purple with the same material, a tin mordant is used. 

 It may be prepared by dissolving tin in muriatic acid, 

 with the gradual addition of nitric acid, then precipi- 

 tating and re-dissolving with potassa. The cloth being 

 impregnated with this mordant and thoroughly dried, 

 is passed through dilute sulphuric acid, to remove the 

 potassa and leave the oxide of tin. After subsequent 

 drying and exposure to the air, the fabric is ready for 

 the dye. 



What are 1001. MINERAL DYES. The dyes de- 



minerai dyes? scr i De d in the following paragraphs, are 

 distinguished from those before mentioned, by contain- 

 ing no organic matter. They consist of colored salts or 

 oxides, precipitated in the fibre of the cloth. Although 

 these substances belong, strictly speaking, to inorganic 

 chemistry, they are here introduced to complete the 

 survey of the subject of dyeing and calico printing. 



1002. PRUSSIAN BLUE. A mineral blue 



How is a min- 

 eral blue ob- may be produced by impregnating cloth 

 tamed? ^^ ^ so i ut i on o f ace tate of iron, before 



