WHY A DYE DYES.

Ashburton Guardian, Volume XL, Issue 9197, 7 January 1920, Page 6

WHY A DYE DYES.

INTEREST ING DETAILS

The answer to this question is given by Bradford Webster in. an article on "A Great American Organic Cliemical Industry," printed as a leading article in "The American Dyestuff Reporter' (New York).. A dye, Mr, Webster tells us, is a coloured .substance which can be absorbed by a fibre or tissue and held so firmly that washing will not remove'it', or light fade it, too quickly. Most dyes arc complex in structure, with many atoms in a molecule. This complexity and size- nF the molecule are undoubtedly essential conditions for the absorption by! the fibre and resistance to washing." He goes on: "The great universal principle of uie positive and the negative, the male and' the female, applies in chemistry as in mechanics, electricity, and life. In chemistry it is.the.acid and the alkaline." Acid dyes are attracted to and colour fibres or tissues of alkaline character, and alkaline or basic dyes are attracted to and oolour fibres or tissues, of acid character. Oppositcs attract; likes repel. "When fibres or tissues do not comply with this principle-they are often made to do so by what are called mordants. Cotton is- made acid by tannic acid and then firmly attracts and holds the.-brilliant-basic dyostuffs like methylene blue, basic- magenta or fuchsin, and .methyl violet. Wool is.made basic with ,chrome mordants so as to attract and. firmly hold alizarine and other, acid dye's. ■'•',.-. '• .■• -■■■•■-•■• •-■"' "There are many natural vegetable dyestuffs and some animal ones. Logwood conies from-the West indies and the extract make a lustrous deep black for wool. Indigo comes from China and British India is the original fast blue* and the. most famous vegetable dyestuff. The acid from the cochineal bug of Mexico is the most famous animal dyestuff and gives a brilliant scarlet. The vegetable dyes are mostly) composed of carbon, oxygen, and hydrogen only. "The great modern dyestuff industry, however, has to do more largely with synthetic dyes, made by intricate chemical processes from derivatives of coal-tar like benzine, toluene, aniline, and phenol. Carbon, hydrogen, .oxygen, nitrogen and sulphur are the principal dements which make up the finished dyes, carbon and hydrogen, appearing in all and in the largest proportions. "The great range in shade and character of "the •many thousands of aniline or coal-tar is due entirely to the proportions x and mode of association in the molecule of the atoms of carbon, hydrogen, oxygen, and one or more other elements. The highest constructive genius in the science of chemistry and isome ,of the .'most brilliant reasoning in all."-science have been shown by -olio merj who have- worked' out and proved what we know of the complex and 'varied arrangements-of the atoms of carbon, .hydrogen, oxygen, and other- elements in the molecules of organic chemicals .like dyestuffs or dyes.

"A most interesting general 'aspect of this question of the arrangement of the atoms in the molecule is the effect on brilliancy and fastness. The brilliant basic colours have a very loose molecular structure, broken down in the course of time by the action of light with comparative ease. 'But in the very fast colours the groups of atoms arc very closely ■ interwoven or interrelated, so that there is tremendous power to resist any disintegrating action of light or other radiant energy. In anthracene, from which the fastest known colours are .derived, three groups of carbon and hydrogen atoms arc so closely interelated that this might-well bo "called the Siamese trip-

lot of organic chemistry. Colour is 'a Jesuit of.the fact that some of the rays of the sun ure reflected by certain organic chemicals, while others are absorbed. A blue colour is produced Avhen the blue rays are reflected and all others arc absorbed. Thq, very fast ( colours are dull.' Probably this is due to the fact that the closely interwoven relation of groups of: atoms in the molecules of fast colours blurs the .•■sharp,' clear reflection of. the looser structures. This is one of the conditions' we should ..understand better ii -.0 knew more about the movement of •"lie atoms in''the. molecule. "In several cases it is known just bow changes in the proportions of the atoms and the assembling of. groups in tho molecule change .shades. For example, the addition of a group oi lour atoms, one carbon and throe hydrogen, in the structure of the molecule, makes the colour bluer ,

"There is unlimited field for the American chemical c nginoer for fen years in perfecting manufacturing -apparatus and processes for ,making known dje-

stufrs in, quantity, reasonably perfect chemically, • and;, with reasonable economy of manufacturing cost. And tliero. is and will be for an indefinite period an unlimited field for tho inventor, anci scientist to": discover new ■chemical, combinations thafe ,wili produce;'wore brilliant fast colours desirable. m tln> complex field of colouring silk, wool, cotton, paper, leather-, feathers; ■!■ My ink, and many other materials wiflr which we are familiar.'• : J