72 The Microscope. 



ist are the Benzidin colors as Congo red, of which there are 

 several kinds made by combining with Benzidin, C12 Hg (NH2 )2, 

 various sulphonated phenol derivatives. 



Many of these dye directly, otherwise with a little alkali, giv- 

 ing some shade of red, which changes to blue by the addition of 

 a weak acid. 



Eosine may almost be regarded as the name of a class of dyes, 

 60 many varieties are called by this title, alone or in combina- 

 tion. They are derived from fluorescein, Cg H12 O5, which is 

 one of the most intense coloring substances known, though not 

 fast. It is said that one part in 2,000,000 in water may be 

 readily observed. This enables it to be used to detect leaks in 

 pipes, etc. 



Its derivatives made with haloids and alcohol radicals, are much 

 used in microscopical work. As with other popular dyes, it is 

 impossible to specify the characters of any particular specimen, 

 unless the maker's name and exact trade name are known. Per- 

 kins' violet, Mauvein, Rosein, Anilin violet, Mauve, Purpurin, 

 Phenamine, Tyraline are a few of the names of the first of the 

 carbon colors that came into commerce, obtained by the oxida- 

 tion of commercial anilin. It is not so much used as formerly, 

 but is the main ingredient of the inks used for rubber stamps. 



Alizarin chemically is different from the preceeding, being 

 derived from anthracene, and forms the base of a great variety 

 of colors, according to the mordant used, from yellow through 

 red to black. Anilin blue, soluble blue, Nicholson's blue, and 

 methyl blue are compounds of tri-phenyl rosanilin, and in some 

 cases admit of direct dyeing. 



It is impossible to classify these substances so that the general 

 reader will obtain any information therefrom. The chemist 

 looks upon them as derived from anilin and its homologues, 

 phenol or carbolic acid, alizarin, etc, while the dyer considers 

 them as different kinds of a color, as alizarin blue, crocein scar- 

 let, etc., But the same article may be produced by different 

 processes of manufacture, and the same color by dyes entirely 

 different in other characters, as fastness to light, soap, etc. 



As every one is produced by some peculiar chemical process, 

 first described in some journal, or in a patent, it has become cus- 

 tomary in technical literature, to identify them by the number 

 of the patent, or the book where first described, and this is the 

 most certain and shortest way of doing it. 



