C 175 3 iS2 



APPENDIX. 



TREATISE ON DYING SILK. 



To cleanse Silk. 



This operation consists in depriving silk of the principles which af- 

 fect its whiteness and flexibility. Monsieur Roard read before the 

 institute of France a very interesting memoir on this subject; of 

 which the following is the result.* 



1. That all unbleached yellow silk contains gum, coloring matter, 

 wax, and a volatile odoriferous oil, analogous to essential oils, extract- 

 ed from many vegetables. 



2. That all white, unbleached silks, yield, also, gum, wax, and 

 oil, slightly colored, which seems to bear some relation to the liquor 

 contained in the chrysalis of the silkworm. 



The gum is dry, friable, and, when powdered, is of a clear, yellow- 

 ish, red color, soluble in water, but scarcely soluble in alcohol. It 

 amounts to from 23 to 24 per cent. The coloring matter is resinous, 

 of a reddish brown color, and of a beautiful yellowish green, when 

 powdered, and of a strong odour; soluble in boiling soap and water, 

 scarcely in caustic alkali. It exists in the proportion of from -^^ to j\ 

 per cent. 



The wax is hard, but brittle, and slightly coloured: insoluble in wa- 

 ter, but easily soluble in alkalies and soap. The fine silks of China, 

 Saint Ambroix, and of Rocquemai-re, have much less of this substance 

 than the other unbleached silks of France, and especially those of 

 Italy. The proportion of wax is from ^l^ to 3 i^ of the weight of silk. 



3. That the silks which yield the finest white, are the very white 

 unbleached silks, and the yellow unbleached silks of a fine golden co- 

 lor: and that all the other silks, which are more or less dull, and in 

 which the gum has undergone any change of condition, either by rea- 

 son of sickness, or bad nutriment of the worms, or by the destruction 

 of the chrysalis in too great a heat, or by winding, ill-conducted, will 

 never attain more than a dull white, always somewhat colored, unless 

 they be exposed, in the unbleached state, to the action of sulphureous gas. 



4. That light bleaches the yellow and white silks, without altering 

 their lustre, or their solidity; and that this agent may be employed 

 to much advantage, either before or after they are cleansed. Four 

 or five days exposure to the sun is sufficient to efiect this object. 



* Memoirs of the Institute, for the year 1808, (class of Mathematical and Physical 

 Sciences,) vol viii. p. 552. It gives all the particulars of the experiments which led 

 to the above interestin,^ results. Monsieur Roard is a practical chemist, and was 

 formerly director of the diers' department hi the Gobelin manufactoiy of Paris. 



