SILK.

105

An analysis of silk, by M. Mulder, gave for 100 parts:—

Yellow NaplesSilk.

Fibroine.. .. 53*37

Gelatine .20*66

Albumen .24*43

Wax .. .» 1*39

Colouring-matter. 0*03

Fatty and resinous matters .. o*io

White Silk from theLevant.

54*0419*0825 '47

i'ii

0*30

Fibroine has the appearance of silk, but is softer, more flexible, and not sostrong. Heated on platinum foil it swells up, and, bursting into flame, burns,leaving a voluminous coke, which emits a peculiar odour. It is insoluble inneutral solvents and in acetic acid. Fibroine, as well as silk, is soluble in anammoniacal solution of oxide of copper, Schweitzer’s reagent; neither areafted upon by a solution of oxide of copper in carbonate of ammonia. Asolution of silk or fibroine in Schweitzer’s reagent is not precipitated eitherby salts, sugar, or gum, as in the case of a solution of cotton in the same reagent.Dilute acids precipitate a flocculent mass from the solution of silk. Accordingto M. Schlossberger, an ammoniacal solution of oxide of nickel behaveswith silk similarly to Schweitzer’s reagent, but does not adt at all upon cotton.The fibroine of sponge is not adted upon by an ammoniacal solution of eithernickel or copper. A solution of basic chloride of zinc at 6o° Baumedissolves in the cold, and more rapidly when aided by heat, a considerablequantity of silk, forming a viscous, syrupy solution, which, acidulated andthen submitted to dialysis, attains the consistency of a thick starch paste ;when a more dilute solution is submitted to dialysis, a liquid is .obtainedwhich, on being evaporated to dryness, yields a golden-coloured varnish,and this varnish raised to a temperature approaching incipient red-heatassumes, immediately before its decomposition, a beautiful groseille redtinge. When silk is adted upon in the cold by strong sulphuric acid, it yieldsa viscous bright brown-coloured solution, which turns red, and becomescoloured a deep brown when heat is applied. Water does not precipitate thesolution, but the solution thus diluted is precipitated by tannic acid. Nitricand hydrochloric acids also readily dissolve silk at the ordinary temperature,and alkalies precipitate the solution. When silk is adted upon by nitric acidand heat applied, it is converted into oxalic acid. Although silk is notdissolved by dilute solutions of caustic alkalies, these should not be appliedto silk for any purpose, because they cause deterioration of the fibre, removingthe gloss and brilliancy. Concentrated solutions of caustic alkalies dissolve silkand fibroine, and the solution is precipitated by water and dilute sulphuric acid,but the precipitate obtained is altered in composition. When fibroine is heatedwith caustic potash it is converted into oxalic acid. The alkaline carbonatesand ammonia do not dissolve silk; and ammonia may be advantageouslyemployed in the cleansing of silk, especially if diluted with both water andpure spirits of wine. Many shades of dyed silk will not, of course, withstandthis treatment. Fibroine does not contain sulphur, and the two nitrogenisedsubstances which accompany fibroine are also free from sulphur. Fibroineyields 0*3 per cent of ash composed of sulphates, chlorides, alkaline phosphates,phosphate of lime, and magnesia, oxides of iron, manganese, and alumina.