178 



ON BLEACHING SILK. 



of soap is decomposed; and when water 

 from the Gobelins river is used, which 

 contains more calcareous salts, 1.8, or 

 about a quarter of the soap, is rendered 

 useless. 



Raw silk, treated with a solution of 

 soap, yielded as much gum, and more 

 waxy and coloring matter, than when 

 either water or alkalies were employed: 

 and on examining, by means of alcohol, 

 silk that had been treated with different 

 liquids, that which had been treated with 

 a solution of soap yielded very little fat 

 or coloring matter to the alcohol, and 

 much less than the other specimens. 



The stiffness of silk is owing to gum, 

 which forms 23 or 24 per cent, of it. 

 When dry, the gum is friable, and yields 

 a very light reddish-yellow powder; 

 smelling and tasting like extracts. It is 

 not softened by heat, but blackens, and is 

 converted into coal. It is soluble in six 

 times its weight of water, forming a 

 transparent brown-red solution, which is 

 yellow when spread out thin, and be- 

 comes greenish and putrid when exposed 

 to the air. The solution lathers like that 

 of soap. Concentrated sulphuric or mu- 

 riatic acid deepens the color of this solu- 

 tion; nitric acid changes it to a golden 

 yellow; sulphurous acid, and especiall}- 

 the gas, brightens the solution, and 

 changes it to a pale greenish-yellow. 

 Alcohol, of the specific gravity of 0.8293, 

 and 80° Cels. (176° Fahr.,) does not dis- 

 solve this gum. Oxymuriatic acid throws 

 down, from a solution of the gum, an 

 abundant white precipitate, which be- 

 comes reddish in the air; its solubility in 

 water is not altered, but it is rendered 

 soluble in alcohol, whether hot or cold. 

 Alkalies do not alter the solution of the 

 gum, but nut-galls throw down a pre- 

 cipitate. 



The coloring matter, which is only 

 found in yellow silk, is a resinous sub 

 stance, almost solid at 12° Cels. (54° 

 Fahr.,) and entirely liquid at 30° (86° 

 Fahr.,) which forms about -^^ih or Ath 

 per cent, of the silk. It has a strong 

 smell, arising from the volatile oil com- 

 bined with it, which resembles oil of 

 aniseed, and may be separated from the 

 yellovv raw silk by means of alcohol 

 The most concentrated solutions of this 



coloring matter are rendered colorless in 

 a few days by the sun. 



It is not soluble in water, but soluble 

 in 8 or 10 times its weight of alcohol. 

 Caustic alkalies, especially ammonia, has 

 some action upon it. The solution of 

 soap, although it has but little action in 

 the cold, dissolves a greater quantity than 

 the alkalies at a boiling heat. Sulphuric 

 and muriatic acids render it black, but 

 sulphurous acid partly takes away its 

 color. Oxymuriatic acid converts it im- 

 mediately into a solid white substance 

 analogous to wax. 



The wax of silk is found in all kinds of 

 silk, and forms about ^oo^^^ °'' too^^ 

 part of China silk. It is hard, brittle, 

 and slightly colored; it melts at 75 or 80° 

 (167 or 176° Fahr.,) insoluble in water, 

 but very soluble in alkalies or soap. 

 Alcohol, sp. grav. 0.8293, takes up only 

 j/g-^th, of its weight at 20 or 25° (68 or 

 77° Fahr.^) and at a boiling heat, about 

 T^otli or ^i^th. 



The solution is scarcely colored, it 

 grows turbid even while hot, and lets 

 fall white flakes. When cooled, these 

 form a bluish-white mass, whicli di- 

 minishes greatly on drying, and is re- 

 duced to very thin plates, slightly trans- 

 parent. 



White raw silk contains only this wax, 

 and some oil, which with gum appears to 

 give color to silk. 



Silk is usually treated with a solution 

 of soap, in order to render it soft, white, 

 and brilliant, withoutaffecting its strength. 

 White raw silk, boiled for three hours 

 with 300 parts of water, is rendered soft 

 and brilliant; but yellow requires 400 

 parts, and 4 or 5 hours boiling, and even 

 then it retains much of its color. It re- 

 quires Tooth part of pure caustic soda, 

 with the usual quantity of water and 

 usual time of boiling, as when soap is 

 employed, to prepare white raw silk; 

 and j'-gih or -g-^th, to prepare yellow raw, 

 silk. The preparation with soap varies 

 in different manufactories; but, on the 

 average, yellow raw silk to be bleached, 

 requires 60 or 70 chilogrammes of soap 

 for 100 of silk, and at least four or six 

 hours boiling; the white raw silk only 

 SO or 35 of soap, and four hours boiling: 



