INCA Tee £2 25 
THURSDAY, MAY 13, 1886 
THE CHEMISTRY OF THE COAL-TAR 
COLOURS 
The Chemistry of the Coal-Tar Colours. Translated from 
the German of Dr. R. Benedikt, and Edited, with 
Additions, by E. Knecht, Ph.D. (London: George 
Bell and Sons, 1886.) 
“THIS is an excellent little practical manual dealing 
with a subject of great scientific and industrial im- 
portance—a subject the scientific side of which has been 
somewhat neglected in this country, to the inevitable 
detriment of the industrial side. The decline of this 
industry in England is a tempting subject to expatiate 
on; but the moral has of late been pointed with such 
laudable iteration that we refrain from pointing it afresh. 
The state of affairs which prevails with regard to the 
literature of the subject is expressed in the opening words 
of the editor’s preface :— 
“Although England may be called the birthplace of 
the coal-tar-colour industry, it is a remarkable fact that 
the English literature on the subject is very scanty, and 
that which does exist is now almost obsolete owing to the 
rapid strides which have been made during the last ten 
years in the manufacture of the coal-tar colours.” 
There is no doubt about the want, and we think that 
this little work supplies it to the extent aimed at. Both 
author and editor are specially qualified for their task by 
experience in teaching the technology of the subject. 
The work contains excellent introductory chapters on 
the optical properties of colouring matters, the methods 
of testing colouring matters—both spectroscopically and 
with regard to their tinctorial power—on the relation of 
the various fibres to the colouring matters, and kindred 
general questions, of importance both to the colour 
chemist and to the dyer. “ Rule-of-thumb” is every- 
where excluded ; reasons are fully and clearly given. 
The greater part of the work is necessarily devoted to 
the chemistry proper of the coal-tar colours—the chemical 
processes by which the various colouring matters are 
obtained and the reactions by means of which a know- 
ledge of their chemical constitution is arrived at. Con- 
stitutional formule naturally play a very important 
part. : 
Our modern dynamical chemists—some of whom, by 
the way, appear to be censors first and investigators after- 
wards—are never tired of crying out for the abandonment 
of these constitutional formulz on the ground that they 
afford only statical, not dynamical, representations of 
chemical phenomena. Happily, those who have built up 
the German coal-tar-colour industry of the last fifteen 
years on the basis of the benzene theory have never 
shared this opinion ; nor is it shared by our authors, who 
in their little treatise faithfully reflect the methods and 
results of this great scientific and industrial development. 
Doubtless, colour chemists would prefer a dynamical 
formula—one which should indicate, for example, the 
most suitable temperature at which to perform a potash 
fusion, or a nitration, with a few hints thrown in as to 
time of heating, concentration, and so forth—and doubt- 
less the dynamical chemists will in time supply this want ; 
VOL. XXXIV.—No. 863 
but meanwhile the colour chemist feels, taught by experi- 
ence, that his humble and inexact calculus of chemical 
operations, the constitutional formula, is vastly better than 
anything that has been offered in its stead. But as yet 
the dynamical critic does not appear to have anything to 
offer in its stead: like certain dynamztical critics he is 
satisfied with destruction, and his attitude towards con- 
stitutional formule is not unlike that of the dynamitical 
critic towards Constitutions—British and other. 
There is little which calls for criticism in the chemical 
portion of the work: the classification is good, and the 
results of the elaborate investigations of which almost 
every colouring matter of any importance has of late 
years been made the subject are given briefly but in a 
way calculated to make clear to the beginner the sig- 
nificance of such work. We could have wished, however, 
that Dr. Knecht in his editorial capacity had thought 
good to give some account of the researches of O. Fischer 
on flavaniline and chrysaniline, and of Bernthsen on 
methylene-blue. The problem of the constitution of 
these compounds has been solved in a very instructive 
and conclusive fashion—much more conclusively than in 
the case of some of the colouring matters of which the 
constitution is discussed in the present work. 
In the introduction reference is made to the popular 
prejudice which exists against the so-called “aniline 
dyes ”—the collective name by which coal-tar colours are 
known among non-chemists. There is animpression that 
the tints are crude and glaring, and that the colours lack 
fastness. Certainly there are coal-tar colours which sin 
in all these respects. But there is a survival of the fittest 
here as elsewhere : the vulgar shades and fugitive colours 
are being weeded out and replaced by better. The 
accusations come most frequently from persons of an 
eesthetic turn, and it is perhaps too much to expect that 
the strenuous esthete, living laborious days in the 
endeavour to improve his own taste and that of his neigh- 
bours, should be aware that the beautiful and permanent 
Turkey-red, which he so justly admires, is now a coal-tar 
colour, and that even indigo may be made from coal-tar. 
As regards “fastness” of colours, the ideas of the 
general public on the subject may perhaps be gauged by 
a speech which we remember reading, made some years 
ago by a Member of Parliament in distributing the 
prizes at a technical schoo]. Seeking to inculcate the 
duty of thoroughness in work, and desirous at the same 
time to employ only such illustrations as would at once 
come home to every technologist, he said :—‘‘ But it 
would not be thorough work, for example, to daub a wall 
with untempered mortar, or to dye with fast colours.” 
Probably a life divided between politics and sport had not 
permitted him to realise that the fastness of colours is 
distinct from that of race-horses—or of youth ! 
Where there is so much to praise we regret to have to 
record a defect, but we think that hardly adequate care 
has been bestowed upon the proof-reading. The mis- 
prints are unnecessarily numerous, and must sometimes 
be very puzzling to a beginner, especially where, as is 
occasionally the case, they affect complicated formule. 
A list of errata is given, which, however, needs ex- 
tension. Whether, for example, the chemistry of the 
average student of technology will be equal to the 
task of informing him that not sodium _bisulphaée 
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