DEUGS 333 



Class F. Pigment dyes. Colour developed on the fibre. 



Mineral colours, e.g. Chrome Yellow. 



Aniline Black discovered 1862 



Ingrain Azo-dyes (Ice colours) 1880 



Sulphide Dyes 1893 



Synthetic Indigo 1897 



Indanthrene Dyes 1901 



Thio-indigo 1906 



(Adapted from " Modern Dyes and Dyeing," a paper read to 

 the Koyal Dublin Society by Professor G. T. Morgan, F.R.S., 

 1914.) 



CHAPTER XXII 



DRUGS 



IT is perhaps worth while, before proceeding further, to review 

 very briefly the history of the processes by which the chemist 

 has gradually learnt how to build up very complicated substances 

 by bringing together the elements of which they are composed, 

 in other words to produce such substances by what is called 

 synthesis. The first case of the production of a compound pre- 

 viously known only as a result of processes going on in organic 

 living matter is that of urea. 



This is the chief nitrogenous excretory product in mammalia, 

 a smaller amount being thrown off by other animals such as 

 birds. The source of the nitrogen is the protein constituents of 

 the food, and a man on ordinary diet excretes on the average 

 30 to 35 grams (1 oz. to 1J oz.) per diem, almost entirely in the 

 urine. 



By the transformation of ammonium cyanate, HN 4 .CNO, a 

 salt which can be made from wholly inorganic materials, urea 

 CO(NH 2 ) 2 , was obtained by Wohler in 1828. As the formula in- 

 dicates, this change is due to a mere rearrangement of the 

 elements present in the molecule, without addition or subtrac- 

 tion of anything. Such a transformation is called in chemical 

 language an isomeric change. Comparatively little notice was 

 taken of this remarkable discovery for many years, and it was 

 reserved for later times to recognise its significance. Forty years 

 later a Russian chemist, Basaroff, discovered that urea might 

 be formed by the simple action of heat on ammonium carbonate, 



