Page:History of the Royal Society.djvu/331

 'Concerning the weight which Colours give to Silk (for in them 'tis most taken notice of, as being sold by weight, and being a Commodity of great price) it is observed, That one pound of raw Silk loseth four ounces by washing out the Gums and natural Sordes.

'That the same scowred Silk may be raised to above thirty ounces from the remaining twelve, if it be dyed black with some Materials.

'The reason why Black colour may be most heavy dyed, being because all gravitating Drugs may be dyed black, being all of colours lighter than it: whereas perhaps there are few or no Materials wherewith to increase the weight of Silk, which will consist with fair light colours; such as will, having been used, as white Arsenick to Incarnadives. Of a thing truly useful in Dying, especially of Blacks, nothing increases weight so much as Galls, by reason whereof black Silks are restored to as much weight as they lost by washing out their Gum: Nor is it counted extraordinary, that Blacks should gain about four or six ounces in the Dying upon each pound.

'Next to Galls, old Fustick increases the weight about 1 in 12.

'Mather about one ounce,

'Weld half an ounce.

'The Blue-far, in deep Blues of the fifth stall, gives no considerable weight.

'Neither doth Logwood, Cochineil, nor Arnotto: Nor doth Copperas itself, where Galls are not.

'I conceive much light would be given to the Philosophy of Dying, by careful Experiments of the weight added by each Drug or Salt in Dying of every colour.

Rh