254 SCIENCE PROGRESS 



The process was not patented but was kept a secret, as the 

 German Patent Laws at that time, so far from protecting such 

 chemical discoveries, seemed merely arranged to throw them 

 open to the whole world, as in the case of alizarine ; but none 

 the less the composition of the new dye was quickly found out 

 by Dr. Martius (who with P. Mendelssohn-Bartholdy had 

 founded the " Gesellschaft ftir Anilinfabrikation " in Berlin), 

 and numerous other firms besides the Badische firm began 

 its manufacture. 



In 1874 Caro also made another important substance for 

 the first time, nitroso-dimethyl-aniline, which forms the basis 

 for many valuable colours such as toluylene blue, meldola blue, 

 gallocyanine, and so on. The divergence in the methods adopted 

 by the German firms and the British firms also becomes evident 

 about this time. The English firms appeared to be content to 

 go on making use of the original alizarine process, without any 

 attempt being made to carry on researches to investigate the 

 possibility of producing new dyes from alizarine or anthracene. 



In Germany, however, unceasing efforts were devoted to 

 research work leading to the manufacture of alizarine orange 

 in 1875 by Caro and the Badische Company on a technical 

 scale, and opening the way for a whole series of new dyes 

 derived from alizarine, such as alizarine blue, discovered by 

 Prudhomme in 1877, alizarine blue, S., discovered by Brunck 

 in 1878, and many others. 



In 1876 Caro prepared methylene blue, a very valuable 

 dye for cotton and prints, and also of interest as forming the 

 subject of the first German dye patent under the new Patent 

 Laws which came into force on July 1, 1877. 



This same year is a notable one in the history of the syn- 

 thetic dye industry, since in that year Griess published his 

 researches on diazo-compounds and so inaugurated a period 

 of enormous activity in the synthesis of azo-dyes. 



When it is remembered that with the components known 

 to-day several millions of azo-dyes can theoretically be made 

 from them, and that actually many thousands of such bodies 

 have been made to determine whether they are suitable for 

 use as dyes, it will be realised what a momentous event the 

 publication of these researches meant. 



Actually the azo-dyes form by far the largest class of dye- 

 stuffs known to-day. 



