M. TECHNOLOGY. 551 



a greenish tins;e. Prussian-blue on incineration the fabric 

 leaves a residue of ferric oxide, proportioned in amount to 

 the intensity of the color. Indigo-blue leaves no ash, except 

 that of the fabric itself, which is white and light. Aniline- 

 blue, like indigo-blue, leaves no ash but that of the fabric ; but 

 it is easily distinguished from it, since the color can be ex- 

 tracted from the fabric by alcohol, and it is distinguished from 

 logwood by means of citric acid, which does not redden it. 



II. Yellow. Rust-yellow, picric acid, turmeric, fustic, 

 Persian-berries, and quercitron are the most preferable yel- 

 lows. A. In order to recognize the different colors, the pres- 

 ence or absence of rust-yellow and picric acid must first be 

 determined. 1. Immerse a sample in warm, slightly acid so- 

 lution of yellow prussiate of potash rust-color will be indi- 

 cated by a blue coloration ; 2. Immerse another sample in a 

 solution of cyanide of potassium, picric acid will yield a 

 blood-red coloration. B. If picric acid and rust-yellow are 

 both absent, place another sample in a boiling solution of 

 one part of soap and 200 of water: l.It turns reddish-brown 

 and becomes yellow again with an acid turmeric; 2. It 

 turns quite dark fustic ; 3. It is unaffected weld, Persian- 

 berries, or quercitron. To distinguish between these three : 

 boil a fresh sample briskly in sulphuric acid, color of weld 

 will disappear, of the others remains; then boil a fresh sample 

 in a tin-salt solution, when a change of orange indicates Per- 

 sian-berries, and no change, or a very slight one, quercitron. 

 C. Annatto, if it happen to be the dye-stuff, may be detected 

 by the greenish-blue color imparted to a sample of the fabric 

 dipped in concentrated sulphuric acid, it being the only yel- 

 low that gives this reaction, and it is also unaffected by 

 chlorine, which decolorizes the yellow of quercitron, turmer- 

 ic, Persian-berries, and weld. 



III. Red. Cochineal, Brazil-wood, madder, saffron-carmine, 

 and aniline-red are to be considered. A. Dip four separate 

 samples of the fabric into boiling soap -solution, ammonia, 

 lemon-juice, and a mixture of equal parts of tin-salt, hydro- 

 chloric acid, and water: 1. No change in any of the samples 

 indicates madder ; 2. Any change indicates the absence of 

 madder, and the presence of one of the other four reds: ,thus 

 complete decoloration by the soap-solution, especially if the 

 color does not return, with its peculiar shade, after the fabric 



