122 FORMATION OF PARTI, 



colours. Now aniline consists of 12 equivalents of carbon, 

 7 of hydrogen, and 1 of nitrogen. It is a compound 

 radical : it is ammonia in which one equivalent of 

 hydrogen has been replaced by the radical phenyle, 

 consisting of 12 equivalents of carbon and 5 of hydrogen. 

 It may be remarked that in all these chemical operations 

 the quantity of carbon has remained the same. 



Aniline is a colourless liquid, and, being an analogue 

 of ammonia, it readily combines with the different acids 

 to form the beautiful coal tar dyes, for which the world 

 is indebted to the brilliant researches of Dr. Hofmann, 

 professor of chemistry. 



By combining a solution of the chloride of lime with 

 the colourless liquid aniline, he obtained the beautiful 

 colour mauve, but it could not be used as a dye till it 

 was rendered permanent by his pupil, Mr. Perkins. 

 His next discovery was the rich crimson crystalline 

 dye magenta, which M. Yerguin first introduced into 

 trade at Lyons as a dyeing agent. It may be produced 

 by mixing the anhydrous bichloride of tin with aniline 

 and then driving off the excess of aniline by heat. 

 Other metallic chlorides, nitrates, and many oxidizing 

 agents, have the power of converting aniline into ma- 

 genta ; as for example when the two colourless liquids 

 acetic acid and aniline are mixed and heated, a chemical 

 combination takes place in which three atoms of ammonia 

 have coalesced into one, a salt is formed which is the 

 acetate of aniline or magenta. Here two liquids unite 

 to form a solid and as in many other instances the 

 resulting substance has the power of decomposing light 

 which neither of its constituents can do. Magenta has 

 a redder tint than mauve, and on that account it is 

 sometimes called aniline red. Professor Hofmann has 

 discovered quite recently that pure aniline has not the 

 property of producing these colours, but that they ori- 

 ginate in an impurity of the aniline called toluidine. 



