Improvements in Dyeing.

Scientific American 30, 9.4.1853

The following process for obtaining a new description of blue and extracts of madder have been lately introduced into notice in France, and are now translated for the first time into English from "D'Invention", a foreign publication to which we are often indebted for much useful information on the arts and manufactures abroad.

A New Blue
If in an alkaline molubdate there is precipitated after the addition of a phosphate all the molybdic acid that it contains where will be obtained in the form of a fine powder a bright citron yellow color which is wonderfully increased by adding a few drops of nitric acid. Caustic alkalies and carbonates of the same dissolve this powder after it has been washed and dried, and furnish a transparent solution from which it is precipitated by acids without any change of color. For example by dipping a piece of cloth in soda, and transferring it to a concentrated acid solution the yellow coloring matter is precipitated on the surface in very great purity.

This powder exhibits very great sensitiveness in presence of the reducing metals, for example by rubbing a small quantity of this powder with a cork and adding a few streaks of chlorohydric acid on a piece of tin, there are obtained in succession every imaginable hue, from yellow to the deepest blue. This property is turned to account by dipping the fabric, when taken out oft he acidulated bath, into a solution of the chloride of tin, by which it is colored to a deeper or lighter blue, according to the quantity of tin contained in the solution. This product offers, in printing calicoes and other fabrics, and advantage that had hitherto been with difficulty realized, and whose results still left much to be desired, namely, that of being able to produce on goods, blues of an extreme purity on a yellow ground, or the contrary.

Madder
A new method of making extract of the above dye has been lately patented in France. Madder in powder, or the flower of the same, is steeped in a neutral organic oxyde, such as the hydrate of methylene, acetone, &c., whether these oxydes are alone or mixed with alcohol or other ethereal matters. The madder may be used either wet or dry, according to the degree of richness that it is required to give the extract that is being manufactured. After having been steeped for a certain length of time, the ligneous substances remaining in the solution are submitted to the pressure so as t oextract entirely all the coloring matter thet they contain. The coloring matter is then precipitated by adding water to the solution and afterwards separated by means of a filter. It is then dried, and can be warehoused or sent away immediately. It is to be observed that by this process neither the madder nor the solutions made use of are submitted to the action of heat, by this means we acoid the noticeable changes that the last-named agent exercises over coloring mater. If a quicker precipitation of teh extract of madder is required instead of employing water alone for this purpose, it can be used acidulated with sulphuric acid, but in this case the precipitate must be carefully washed until it presents no further acid re-action. Unless this precaution is taken the employment of the extract of madder thus obtained would be detrimental on account of the re-action of the acid that would ensue. Another way of obtaining a new dye from madder, which has received the name of "Rubiacine" has been likewise lately patented in the same country. The madder is placed whole or pounded into an alkaline solution in which it is left to steep for two or three days. At the expiration of this period the solution is neutralized by means of acidulated water, any alkali and acid may be used for this operation. It is then poured altogether in a filter and slightly pressed, after which it is evaporated, and the so-called "Rubiacine" is obtained solid, it is tehn pounded and put up in casks. This material possesses dyeing properties equal to four times that of madder powder, and equal weight for weight to the extract of the same, it is particularly noticeable for the property that it possesses of dyeing cotton a Turkey red.