[ 4 * 4 ].

weight before-mentioned, on being boiled in a solutionof alcaline salt, received a further diminution of two-thirds : another quantity of the fame silk being boiledlonger with the alcali, about four-fifths of its weightwere taken up by the liquor, which became reddish, andthe remaining fifth was an incoherent friable mass, notill resembling papier mache. It should seem from theseexperiments, that even the common process of cleansingsilk, in which a fourth of its weight is dissolved, cannotbe entirely innocent, but must contribute in some degreeto diminish the strength of the silk; and accordingly Ifind it allowed by the workmen, that a thread of silkboiled is not so strong as when raw. Some further ex-periments of the effects of different substances on rawsilk are now in hand : if any thing of importance resultsfrom them, they st;all be communicated in the appendixto this volume.

Silk is rarely or never dyed of a blue as a preparatoryground for the black dye. The regulations of the Frenchsilk dyers expressly order its being dyed directly fromwhite to black, and this, as I am informed, is the generalpractice among us, though some report that the Germansilk dyers give a brown ground for their black silks, byboiling them with the root or bark of the walnut-tree.The only reason I have heard assigned for the omission ofthe blue ground on silk is, its adding to the expence of aprocess, which is otherwise, as commonly managed, con-siderably more expensive and troublesome than the dyingof woollen.

Mr. Macquer reckons black a difficult colour to dye onsilk: and indeed, if all the circumstances, and materials,of the complex process, which he describes as being fol-lowed in many of the good dye-houses of France, werenecessary for succeeding in the colour, a multitude of

trials