COLOURS FROM ANILINE.
173
remark that the aniline of commerce is not prepared in this manner. Itssource is coal-tar, which contains, according to the most recent investigations,upwards of fifty distindt bodies. These are classified in three groups, accordingas they are acid, neutral, or basic. Others divide them into hydrocarbons,consisting of hydrogen and carbon only; oxygenated or sulphuretted com-pounds free from nitrogen ; and, lastly, nitrogenised compounds, analogous toammonia. Amongst these aniline also occurs, but in so small a proportion,scarcely amounting to 0’5 per cent, that it is of no pra&ical value. It may,if desired, be extracted by treating the products coming over between 150° and200 0 C. with dilute sulphuric acid, and subsequent decomposition of the sulphateof aniline thus obtained with hydrate of soda or milk of lime. Hofmann’sprocess, described in the Annetlen der Chemie und Pharmacies vol. xlvii., p. 30,maybe also applied. Aniline is therefore manufa<5tured in an indired mannerfrom benzine or benzol,—another of the coal-tar produfts, which thusbecomes the starting-point of the aniline colours.
Benzol was discovered by Faraday, early in the present century, amongthe produ&s of the oil gas manufa&ure. It is obtained pure by distillingbenzoic acid with three times its weight of hydrate of lime. By this processbenzol is obtained as a colourless, highly mobile fluid, of sp. gr. 0*85, andboiling at 85° C. When cooled down to o° C., it forms a crystalline mass,which liquefies at 7 0 C. Benzol is insoluble in water, but dissolves readilyin alcohol and ether. It is a true hydrocarbon, consisting only of carbonand hydrogen. Its formula is Cj 2 H6. This substance is present in the stateof vapour in common coal-gas, from which it may be extra&ed by treatingthe gas at a low temperature with alcohol, or, better, petroleum oil, fromwhich solvents the benzol is separated by re&ification at a very gentle heat.As yet benzol is chiefly, if not solely, obtained from coal-tar. This liquidis distilled in suitable apparatus.* The benzols (mixtures of hydrocarbonshomologous with true benzol), which pass over between 8o° and ioo° C. arecalled light benzols. Those colletted from ioo° C. to 130° C. are known asheavy benzols. The produ&s thus obtained are converted separately intonitro-benzols. The benzols of commerce consist chiefly of the hydro-carbons, benzol, and toluol, cymol and cumol being present in small quantitiesonly.
To give an idea of the contents of several species of coal-tar, we add herethe results of investigations made on this subjeft by Dr. Grace Calvert.
*0
M
a
”3
0
c
u
c
> Ort c
u .J3
aU
£
.c
£
a.
3
>*
m
CU
X
a,
£
Q
The tar of Boghead coal contains ..
12
3
30
41
O
14 p.c.
,, Cannel .
9
14
40
0
15
22 „
1, Newcastle..
2
5
12
0
58
23 ..
,, Staffordshire.
5
9
35
0
22
29 „
The benzol is treated with a mixture of strong nitric and sulphuric acids,and is thus converted into nitro-benzol, C I2 H 5 N0 4 . This latter substanceis converted into aniline by means of a process invented by Bechamps. 100
* See Reimann’s Handbook of Aniline, p. 3.