112 Transactions of the 



mixed with 1 or 2 per cent, of sulphur. Impure sal ammoniac is 

 now largely us. 1 as a manure. Coal tar itself is of little use, but it 

 contains some mi st important constituents, snch as benzene, phenol, 

 and picric acid. The crude liquid is subjected to repeated distillations, 

 the more volatile and li aid hydro-carbons together with alcohols and 

 ethers pass over first.' After the distillation has continued some time, 

 a residue is left, consisting of pitch or asphalt, also solid hydro- 

 carbons, together with resinous compounds. It would be waste of 

 time to describe the numerous uses these bodies are put to, as they 

 are so numerous and manifest. The distillate, therefore, from the 

 crude tar will engage our attention now. 



The more volatile portion consists of " hght oil," or naphtha, com- 

 posed mainly of benzene and its homolognes, while " dead oil," or the 

 less volatile part contains phenol and cresol, also aniline, i)icoline, and 

 a number of solid hydro-carbons, including naphthaline, and anthra- 

 cine. All the above-named substances are vahiaiile for some reason, 

 especially benzene. This interesting and extremely valuable product 

 of coal boils at 82° C, and therefire passes over with the first portion 

 of the distillate It is pi-epaied pure by repeatedly washing with 

 H2SO4 and Na HO, tlie coal-tar oil, to remove acids and alkaline 

 products lilvewise existing in it ; the neutral oil thus obtained is sub- 

 mitted to repeated fractional distillations. It is now prepared in 

 immense quantities for the manufacture of aniline, Avhich plays such 

 an imjiortant part in our dye works. Benzene is a thin, limpid, 

 colourless liquid, having a power of dissolving iodine, sulphur, phos- 

 phorous, and resius, hence it is used in many chemical preparations 

 and for removing grease sjjots from articles of dress. 



By acting on benzene with the strongest nitric acid, nitro-benzene is 

 formed ; this substance has a peculiar almond-like smell and taste, 

 and is extensively used for scenting soaps. It was used as a flavour- 

 ing agent, but so many accidents arose from its poisonous character, 

 that this practice has been discontinued. From benzene is made the 

 highly interesting substance, aniline, which finds an extensive appli- 

 cation in the arts, a long series of colours unequalled in brilliancy 

 aud beauty having, by the action of different oxidising agents, been 

 produced irom it. I think it will not be out of place to look shortly 

 into the modes of preparing a few of the most important. Aniline- 

 purple, or mauve, is obtained by mixing a solution of aniline sulphate 

 and potassium bichromate, and allowing the mixture to stand for 

 several hours ; the black precipitate is filtered off and purified from 

 admixing potassium sulphate by washing with water. It is then 

 dried, aiid freed from resinous matter by repeated digestion with coal- 

 tar na]jhtha, and finally dissolved in alcohol. It is then usually 

 purified further by evaporating to dryness, and dissolving the residue 

 in boiling water, re-precipitating with soda, and dissolving in alcohol 

 again. 



Mauve thus prepared forms a brittle substance, having a bronze- 

 coloured surface ; it is with difficulty soluble in cold water, though it 

 imparts a deep purple colour to it. 



