TUE 7VNALYSIS OF SILK. 23 



Caustic soda solution is added to this mixture drop by drop until ilu' hydrated oxide 

 of eopj)er, at first precipitated, is again dissolved. Excess of caustic soda is especially to 

 be avoided. 



On placing the mixed fibres in the blue liquid thus obtained, it was found that the 

 silk was completely dissolved in the course of from two to three hours at the ordinary 

 temperature. The process may be hastened by stirring the liquid from time to time. 

 The w^ool, under the action of the same reagent, became blackened, probably from tlio 

 action of the sulphur of the wool on the copper of the solution. Cotton and linen merely 

 acquired the blue colour of the solution. The colour in each case was easily removed on 

 placing the wool, cotton and linen together for a few minutes in dilute hydrochloric acid, 

 when the fibres acquired their natural colour. The same strength of acid-w^as used as in 

 the preliminary cleansing of the fibre so as to avoid any additional loss from this source. 

 The residues w^ere then carefully washed and dried at 100" C. 



Average of six analyses :— 



Silk, completely dissolved. 



AVool, lossof 3.48%. 



Cotton, " 0.24%. 



Linen, " 0.33%. 



One sample set was allowed to remain for eighteen hours in the copper solution, and 



yielded the following results : — 



Silk, completely dissolved. 



Wool, I0S.S of 3.84%. 



Cotton, " 0.22%. 



Linen, " 0.34%. 



It would seem that this reagent thus yields results w^hich ai-e quite reliable as a 

 means of separation between silk and cotton or linen, while not so reliable as a quantitative 

 method for a texture containing silk and wool. 



Basic Zinc Chloride. — Persoz (Moniteur xdenlifique, Series -3, Vol. X. p. 336,) and 

 E,émont more recently (Chem. Zeit., 1881, No. 51, p. 972,) hav^e advocated this reagent as a 

 solvent for silk. It is prepared according to their directions by dissolving 100 grs. zinc 

 chloride in 85 c.c. water, adding to the solution four grs. of zinc oxide, and heating until 

 dissolved. In this reagent silk dissolves rapidly, (if hot, in one to two minutes) ; wool 

 seems scarcely at all to be atiected, while cotton and linen are both attacked, and more 

 particularly so if the solution is not sufiiciently basic. After treatment the residues were 

 warmed with dilute hydrochloric acid, as in case of last-mentioned reagent, and boiled 

 with water and dried at 100'. 



Average of six analyses: — 



Silk, completely dissolved. 



Wool, loss of 0.49%. 



Cotton, " 1.74%. 



Linen, " 3.67%. 



As distinguished from the alkaline glycerine solution of oxide of copper, this reagent 

 seems best adapted for the separation of silk from wool, while not so well adapted to the 

 separation of silk from cotton or linen. 



