New Blue Color Wanted.

Scientific American 11, 12.9.1863

For army clothing, blue has been more universally adopted than any other color. It is possible to dye cloth this color by several processes and different substances; but the exigencies of a soldier's life demand that the color of his clothing should be permanent - that is, unchangeable by exposure to the sun and weather, and the action of alkaline solutions used for washing. Hitherto, only one substance has been generally used, possessing the best qualities for producing this color. It is known by the name of indigo, and is manufactured from a plant into small hard cakes, in which condition it is transported from tropical and intertropical regions, where the plant is cultivated. As a coloring substance, indigo has been employed in Africa Asia, and South America, from time immemorial. The color which it imparts to cloth possesses the excellent quality of appearing fresh as long as the fabric endures. WIthin the past two years, the demand for blue army cloth has been so great, that it has been difficult to obtain a supply of indigo for dyeing; more especially as the best qualities of the drug have of late years been imported from sections in the East indies, where there have been serious disturbances among the ative cultivators of the plant. Its price - at all times high - has advanced from one dollar and a half to two dollars and a quarter per pound; and a sufficient quantity of the best qualities cannot be had at all. The introduction of a cheaper substitute for this material, would be of great importance to the community; and would undoubtedly realize a fortune to the inventor.

Within the past three years, colors manufactured from the products of coal tar, have come into very general use, and have superseded colors that were formerly derived from decoctions of various plants and "dye-woods." But the range of these new colors is limited, being chiefly confined to shades of purple and red. It is true that emeraldine - a green coal-tar color - has been manufactured; and also blue - termed azuline; but the latter does not possess the durable qualities of that produced from indigo. Still we think that this is the direction to which the chemist should look, as the most hopeful field in which he can labor for obtaining a substitute for indigo. The base - aniline - of coal colors was first obtained from indigo by distallation. Rosaniline is composed of C₂₀ (carbon), H₁₉ (hydrogen), N₁₃ (nitrogen); and blue indigo is composed of C₁₆H₁₀N₂O₂ (oxygen). What is called "white indigo" aimply contains two atoms more of hydrogen than the blue indigo. There is therefore a close relationship between these colors and substances. The aniline blue which is now made for dyeing silk, is manufactured from the rosaniline producs, by acting upon them with acids, under heat, in a close vessel; so that it is reasonable to conclude that a perfect substitute for indgo may be made from the products of coal tar. It is also much to be desired that the new blue color should be as easily applied to woolen fabrics, as the new red and purple colors are dyed upon silk and wool. These require no mordants; the fabric is dyed by simple immersion in a warm bath of the coloring agent. In dyeing wool with indigo, the vats afor the goods are very difficult tomanage, and are easily spoiled, because the indigo requires to be deoxidized by fermentation, before it will yield its coloring matter to cloth. Woad, bran, madder, &c., are employed as fermenting agents, and much experience and great skill are necessary to manage the operations. Large quantities of indigo are frequently rendered useless, for want of a little care and skill in preparing and managing indigo vats. A new color may be produced to obviate these difficulties, by which blue cloth may be dyed as permanently as with the best Bengal indigo. Never before has out country resented so great a prospect of reward to the discoverer of such a color. Our home woolen manufactures have increased to a prodigious extent during the past two years; and they must attain to still greater importance, as they are necessarily taking the place of cottong fabrics for many purposes.