M. Persoz on the Solubility of Silk. 215 



states, for they are contained in the mother-liquor from the pre- 

 paration of the latter. They are easily obtained by boiling the 

 solutions of the acid tungstates with gelatinous silica. The 

 potash-, soda-, and ammonia-salts are all as yet studied. They 

 are soluble, and crystallize well. In many respects their solu- 

 tions comport themselves like those of the metatungstates. They 

 are very stable, and are not decomposed by treatment with hy- 

 drochloric acid, and are only converted into acid salts. By fusion 

 with alkalies they are converted into a mixture of tungstates and 

 silicates. They all appear to contain ten equivalents of tungstic 

 to one of silicic acid, and the neutral salts contain four equivalents 

 of base. These ratios it is convenient to double, and represent 

 the neutral silicotungstates by the general formula 



8MO20WO 3 ,2SiO 2 , 



so as to include in this formula the acid and double salts. The 

 following are some of those which Marignac has already ana- 

 lysed : — 



8NH 4 0, 20 WO 3 , 2Si0 2 + 16 Aq, 



7NH 4 0, HO,20WO 3 ,2SiO 2 + 24Aq, 

 3NH 4 0,5 HO, 20 WO 3 , 2Si0 2 +18Aq, 

 3K0, 5 HO, 20 WO 3 , 2Si0 2 + 26Aq, 

 3NaO, 5 HO, 20 WO 3 , 2Si0 2 + 17Aq. 



M. Persoz, jun.*, has found that silk rapidly dissolves in a hot 

 concentrated solution of chloride of zinc, and more slowly in the 

 cold. The solution used marked 60° in the areometer, and was 

 boiled with oxide of zinc, so that it was basic ; it became cloudy 

 on the addition of water from the precipitation of a basic chlo- 

 ride. The solution thus prepared dissolves silk without attacking 

 either wool or vegetable fibres. In any mixture of the three the 

 silk may be dissolved by chloride, and the wool destroyed by 

 soda, so as to preserve only the vegetable fibres. It thus affords 

 a means of discriminating the complex nature of certain tissues. 



Chloride of zinc can dissolve such a quantity of silk as to be 

 entirely viscous, and capable of being drawn out like a thick 

 syrup, resembling a concentrated solution of gum-arabic. Am- 

 monia produces, in a solution of the silk diluted with water, a 

 precipitate readily soluble in an excess of the reagent. 



Persoz submitted this solution, diluted with water acidulated 

 by hydrochloric acid, to the action of the dialyser. The chloride 

 of zinc passed in large quantity; the liquid became more viscous 

 and then increased in volume, forming an opaline jelly like starch 

 paste. It still contained a small quantity of zinc, from which it 



* Comptes RenduSy December 22, 1862. 



