Fuly 30, 1885] 
NATURE 
395 
The first of these processes consisted in passing nitrous acid 
into commercial aniline, and then heating the mixture with 
arsenic acid, and then extracting the colouring matter produced. 
Hofmann examined this, and showed that it had the formula 
Cy,H. Ny (Ber. vi. 526, 1872). 
The examination of the product which was obtained by oxidis- 
ing the mauve dye, I found to have the composition, C.) Hy, Ny 
(F. Chem, Soc, xxxv. 731), results which correspond with analyses 
published by Dale and Schorlemmer (¥. Chem. Soc. xxxv. 682), 
obtained from the examination of a similar product. This sub- 
stance, I found, was associated with that examined by Hofmann 
in a product prepared by Messrs. Guinon & Co., of Lyons. 
Methods of a more synthetical nature have since then been 
discovered. O. Witt found that safranine could be obtained 
from orthoazotoluene and hydrochloride of toluene at 150-200° 
(Ber. x., 874, 1877). He then found that by oxidising a mix- 
ture of one part of paraphenylenediamine, and two parts of aniline, 
on the application of heat a safranine could be obtained which 
has the formula, C,, H,, Ny, and which is called phenosafranine. 
The formation of this colouring matter by this and other pro- 
cesses has been studied by Nietzki (Se. xvi. 464). He finds that 
the aniline in the reaction, in which paraphenylenediamine takes 
part, may be substituted by other primary monamines, or a mix- 
ture of these with dimethylaniline, and thus a large number of 
these dyes can be obtained. 
Phenosafranine is now produced very largely, and in a pure 
crystallised condition, and is a very useful dyeing agent. 
If we assume that all the safranines are strictly homologous 
compounds, the formula that Nietzki gives for phenosafranine 
would make the formula of that examined by Hofmann, and 
that examined by myself and Dale and Schorlemmer, to be in- 
correct, and that they should contain two hydrogens more than 
are assigned to them. This I cannot think is possible from all 
the analytical results we obtained. 
The constitution of mauvein has not yet been established, and 
I have still experiments on this subject in hand. This may also 
be said of safranine, I think, although Nietzki has proposed a 
formula for it, in which nitrogen occupies a similar position to 
the metharacarbon in the rosaniline series. 
Triphenylmethane Derivatives.—W e must now go back again 
to the early days of this industry to consider the next class of 
compounds—viz., triphenylmethane derivatives. 
The industrial success of the mauve dye caused aniline to be- 
come a very favourite body to experiment with, and the result 
was that in 1859, the discovery of that important colouring 
matter first known as fuchsine or magenta took place. Hofmann 
had observed in his experiments on the action of carbon tetra- 
chloride on aniline in 1858, the formation of a red colouring 
matter, which consisted of this substance as a secondary product 
of the reaction, but it was M. Verquin who first discovered a 
process for the transformation of aniline into a red colouring matter 
of tinctorial value. This discovery of the compound marks a 
most important fresh departure in the history of coal-tar colours. 
As I mentioned, the mauve had paved the way for future 
colouring matters, and this new substance, which could be ap- 
plied to fabrics by the same methods as the mauve, was most 
eagerly sought after owing to the brilliancy of its colour ; and 
probably its manufacture was one of the most successful finan- 
cially of all the aniline colours. 
M. Verquin’s process, which consisted in treating tin tetra- 
chloride with commercial aniline, was soon superseded by better 
processes. The number of patents taken out for the production 
of this dye was very large, and all imaginable products were 
claimed as capable of producing it from aniline. The two most 
important, however, were those in which mercury nitrate and 
arsenic acid were used. The first of these processes, with which 
I had some experience, required much care to regulate the re- 
action and prevent deflagration. The next process with arsenic 
acid, known as medlocks, was by far the best, and was used very 
extensively until the last few years, the use of nitrobenzene as 
poe onidisng agent being now mostly used in the place of arsenic 
aicd. 
The manufacture of magenta, which at this period was often 
called roseine, was carried on chiefly in this country by Messrs. 
Sampson, Maule, & Nicholson, by the arsenic acid process. Mr. 
E. C. Nicholson and Dr. A. P. Price, of this firm, worked out 
the process with great success, and were the first to produce this 
colouring matter in a pure state. The beautiful display of the 
crystallised acetate, shown at the Exhibition of 1862, illustrated ! 
this fully. 
It was with products supplied by Mr. Nicholson that Dr. 
Hofmann made his first researches on this colouring matter. 
He changed its name from roseine to vosani/ine, and found that 
the base, when in combination with acids, had the formula 
Cop Ayo N3. 
The important observation of Nicholson, and the critical 
experiments of Hofmann, on the necessity of using, not pure 
aniline, but a mixture of aniline and toluidine for the production 
of this substance, was made about this period.? 
The next important step in this industry was the use of ros- 
aniline itself asa source of new colouring matters. For this we 
are indebted to the experiments of two French chemists—viz., 
MM. Gerard and Delaire, who discovered that rosaniline salts, 
when heated with aniline, gave violet and blue colouring matters, 
which they called Violet Imperial and Bleu de Lyon. It is, 
however, to Mr. Nicholson that the credit of producing these 
bodies, in a practically pure state, belongs. This especially refers 
to the blue, the product known as opal blue, used by Dr. Hof- 
mann in his investigations on the subject, being of great purity. 
Dr. Hofmann showed that these products were phenylated ros- 
anilines, as is now well known, ammonia being given off in the 
reaction. And I may mention in passing that the manufacture of 
these blues is now carried on to such a large extent that the 
ammonia produced in this reaction is collected for the production 
of its sulphate or other salt. 
One of the difficulties in the way of the new blue was its in- 
solubility in water. Mr. Nicholson, however (in 1862), probably 
thinking of the method used to render indigo soluble, experi- 
mented upon the action of sulphuric acid in this compound, and 
he found that it was possible to obtain sulphonic acids from it. 
One of these, the sodium salt of which is known as ‘‘ Nichol- 
son’s” or ‘“‘alkali blue,” is the monosulphonic acid, which is 
itself insoluble in water, but forms soluble salts, which can be 
applied to the goods, and then decomposed by acids. This com- 
pound has had much to do with the successful introduction of this 
colouring matter. The other product known as soluble blue is 
the sodium salt of trisulpho acid. 
In the early part of 1864 the Hofmann violets were introduced. 
These, as is well known, are the ethylated rosanilines produced 
by acting upon rosaniline with ethyliodide. These colouring 
matters are more brilliant, though much more fugitive than mau- 
vein ; but by this time the desire for permanency was giving way 
very much to that of brilliancy ; and these colouring matters were 
quickly taken up by dyers and calico printers. 
About this time some colouring matters derived from phenol 
were introduced, and which, curiously, are found to belong to 
the class of substances now under consideration. These were 
brought forward by Messrs. Guinon, Marnas, and Bonnet, of 
Lyons. The first product was aurine, prepared from phenol by 
means of oxalic and sulphuric acid (Kolbe and Schavtt’s process). 
The next was polvuine, obtained by acting upon aurine with 
ammonia. The third was azuline, prepared by heating aurine 
with aniline. This last was a blue dye, which has since been 
shown to consist chiefly of triphenylrosaniline. 
Purple and violet derivatives were also obtained from ros- 
aniline by a process of my own, in which brominated turpentine 
was employed. These were known as Britannia violets, and were 
much used. 
Other coloured derivatives were also discovered ; for example, 
by the action of aldehyde and sulphuric acid, a blue product was 
obtained, which, when treated with sodium hyposulphite or 
sulphuretted hydrogen water, yielded the well-known aldehyde 
green. 
~ On examining the action of acetylchloride on Britannia violet, 
I obtained a peculiar green, which was used principally by calico 
printers, and very considerable quantities of acetylchloride were 
prepared for this purpose. The process was not published. This 
green was of a blue shade, and was obtained in a crystallised 
condition in combination with picric acid. The crystals had a 
golden metallic reflection. 
Soon after this it was noticed that a green compound was 
produced in the preparation of the Hofmann violets, though 
generally only in small quantities. It was afterwards found 
that by making rosaniline react with an excess of methylic 
iodide that it could be produced practically. It was called 
iodine green ; but the product now manufactured isa chloride. 
This colouring matter gave good candle-light greens. One of 
2 In my original patent it was shown that -colouring matters could be ob- 
tained, not only from aniline, but also from toluidine xylidine and 
cumidine. 
