October 28, 1910] 



SCIENCE 



599 



■compounds belonging to the azine or pyronine 

 '01- oxyketone or other classes, according to 

 their composition and the arrangement of 

 their atoms or their molecules. They are im- 

 portant and indeed fundamental tools in a 

 ;great industry, and are of interest and of 

 \-alue, not on account of their composition, 

 ibut for their power of coloring various sub- 

 stances useful and valuable shades of color. 

 And everybody who has anything to do with 

 'dyestufFs, outside of a research organic lab- 

 oratory, studies them with this practical end 

 in view. Their number and variety are so 

 ■great that in order to get any idea of them at 

 all they must be classified. But these classes, 

 ■excepting, as before, in some research organic 

 laboratories, are invariably based upon their 

 ■dyeing properties. Not one dyeing chemist in 

 :a hundred could distinguish a thiazine from 

 .a thiobenzenyl derivative; but every one of 

 them, from the gray-haired chief of a great 

 ■color laboratory, to the bright-eyed laboratory 

 boj' picking up points about dyes in the inter- 

 vals of scrubbing the floors or washing out 

 beakers, would know the difference between, 

 for instance, a vat dye and a basic dye — would 

 know how tliey were applied, upon what fibers, 

 with what general results — in other words, 

 ■would know how they were used and what 

 they were used for. These classes are not 

 numerous, perhaps seven in all — the direct 

 ■cotton or salt colors, basic, acid, mordant, vat, 

 sulphur and developed colors. But into these 

 •seven classes, all commercial dyestufl^s, not 

 ■only may be divided, but must be divided, in 

 ■order to have any idea of how they can be 

 utilized. 



The nest most important and most distinc- 

 tive characteristic of a dyestuff is that it dyes 

 some particular color — on wool, cotton or 

 other textile fiber. This furnishes a second, 

 very simple and extremely practical method 

 of subdivision. First, we determine how a 

 coloring matter dyes, and, secondly, what color 

 it dyes. These two tests can be made in a 

 very few minutes, furnish most valuable prac- 

 tical information, and, in a great majority of 

 cases, furnish all the information that it is 

 necessary to know about a color. 



If a dyer is asked to give an estimate on a 

 thousand pounds of cotton yarn to dye to 

 match a given sample, he certainly does not 

 care about the chemical composition of that 

 color, nor, excepting under special circum- 

 stances, about the absolute identity of that 

 particular dyestuff. If the chemist tells him 

 what class the color belongs to, whether a salt 

 color, cheap and not fast to washing, or a vat 

 color, very expensive, and exceedingly fast to 

 both washing and light, or a sulphur color, 

 fast to washing and not to light, or a basic 

 color, very brilliant, quite fugitive in sun- 

 light, needing careful mordanting before 

 dyeing, or even a mordant or alizarine color, 

 with all the trouble and expense that that 

 means — then the dyer can estimate at once 

 the expense of matching that color, and the 

 problem is solved. 



Accordingly, in every dyeing laboratory, 

 and in almost any, if not every, dyeing school, 

 the students are first taught this practical 

 classification, and then the different impor- 

 tant dyes in each class, and what their peculi- 

 arities are. After some experience the chief 

 colors in each class come to have an individ- 

 uality, so that they can be recognized at once, 

 as soon as they are dyed. As one dyeing 

 chemist told me, "It's like recognizing a boy 

 you have known among a crowd of others. 

 You can't tell offhand just what strikes you 

 about him, but 'That's Johnnie.'" And 

 every hour's work on the dyes, working with 

 the practical side in view, teaches more and 

 more about their properties, and enables the 

 problems that come in to be solved more 

 readily and rapidly. 



And this is necessary, for in a dyeing lab- 

 oratory the problems are apt to come in fast 

 and thick. The morning's mail may bring in 

 samples of colors, batches of yarns, scraps of 

 linen, cotton, silk, artificial silk and mixed 

 goods, paper, calico, pigment and the like, in 

 bewildering numbers, all to be matched, and 

 in some eases identified, and all to be finished 

 and cleared up before closing hours, or at 

 latest before next morning's mail is dis- 

 tributed. There is no time here for elaborate 



