RESEARCH AND THE COAL-TAR DYE INDUSTRY 255 



One or two azo-dyes such as Bismarck brown & chrysoidin 

 had been prepared before this date, but their constitution was 

 for the most part unknown, and it was not until Griess's inves- 

 tigations cleared matters up that systematic progress began 

 to be made in this direction, showing once again the close and 

 inevitable co-operation between science and technology neces- 

 sary for the sound development of the industry. 



It was at first supposed that azo-dyes could only be obtained 

 in yellows or oranges, but Caro's discovery of " fast red " 

 in 1879 effectually disposed of these imaginary limitations, 

 and from that date onwards every year saw the production 

 of new azo-dyes of all shades and colours ; one dye in par- 

 ticular deserves notice, namely Biebrich scarlet, discovered 

 by Nietzki in 1879 as being the first representative of the 

 sub-class known as disazo dyes, which have since grown to 

 be of very great importance. 



To Caro we are also indebted for the process of sulphonating 

 various dyes, such as magenta and so on, thus obtaining the 

 class of acid dyes, such as " acid magenta," which are in many 

 respects faster than the original dyes, and have an extensive 

 use in wool-dyeing. 



In 1878 malachite green, which holds an almost unique 

 position in the dyeing world on account of its clear green tone, 

 was prepared on a technical scale, having been discovered 

 by Otto Fischer in 1877 under the name of " Phthalgrun," 

 and it is characteristic of the scientific way in which the German 

 dye industry was managed that when Fischer first announced 

 his discovery of " Phthalgrun " from benzaldehyde and 

 dimethylaniline it was assumed to be of little more than 

 academic interest, since benzaldehyde was a fairly expensive 

 reagent obtainable only in relatively small quantities. Never- 

 theless by May 1878 the Badische Company, under the skilful 

 and energetic guidance of Caro, had succeeded in overcoming 

 most of the difficulties and began to produce the dye on a 

 commercial scale. Professor Bernthsen, therefore (who men- 

 tioned the matter in a memorial address to the German Chemical 

 Society on Heinrich Caro), may be pardoned for his proud 

 boast, " Wenn die deutsche Technik erst einmal Bedarf fur 

 eine Produkt hat, so weiss sie auch alle Hindernisse fur seine 

 technische Darstellung zu uberwinden." 



