TRANSACTIONS OF SECTION B. 781 
nitrogen atoms. This view explains also the well-known fact that a mixed diazo- 
amide is the same in whichever order the amines are diazotised and 
combined. The third isomeride is, in fact, a polymeride; but in spite of this 
inevitable conclusion the depression of freezing-point in benzene solution, as deter- 
mined by Raoult’s method, agrees more closely with the half-molecular formula, a 
fact which indicates that dissociation takes place in solution. The force which 
binds together the constituents of the molecule is regarded by the author as similar 
in nature to that which holds together the constituents in a ‘molecular compound.’ 
6. The Action of Light upon the Diazo-Compounds of Primuline and Dehydro- 
thiotoluidine: a Method of Photographic Dyeing and Printing. By 
ArtTHuR G, GREEN, CHArtes F. Cross, and Epwarp J. Brvan. 
In the early part of 1887 one of us (Green) discovered that by heating para- 
toluidine (2 mols.) with sulphur (4 to 5 atoms) at 200°-300° C. a very complex 
amido base was obtained, which on treatment with fuming sulphuric acid at a low 
temperature was converted into a sulphonic acid, the alkaline salts of which were 
easily soluble in water, and had the peculiar property of dyeing cotton primrose 
yellow from an alkaline or neutral bath without the use of a mordant. Further, 
the amido compound thus fixed upon the fibre could be diazotised in situ by 
passing the material through a weak solution of nitrous acid, and when diazotised 
could be combined with various phenols and amines, thus producing a variety of 
different colours, which, being formed within the fibre, were all distinguished by 
great fastness to washing, &c. The soluble amido sulphonic acid was named 
*Primuline’ by its discoverer, and has found a yery extensive employment in 
cotton dyeing; the colours produced from it within the fibre were called ‘Ingrain 
Colours.’? 
Although the chemical constitution of primuline base (of which primuline is 
the mono-sulphonic acid) has not yet been determined with certainty, there is no 
doubt that it is a condensed derivative of dehydrothiotoluidine, a body which 
-always accompanies it in its formation, and that it differs from the latter in exactly 
the same way as dehydrothiotoluidine itself differs from para-toluidine. As there 
is scarcely any doubt that dehydrothiotoluidine has the formula—- 
O,H,(CH,) << >0.C,H,(NH,) 
#.e., is an amido-benzenyl-amido-thiocresol, it follows that the formula of primuline, 
or rather of its chief constituent, is? probably 
CHy(CH) CN >O.0,H <p >0-C,H sy >C.C,H,(S0,Na)(NH,) 
In a similar manner by heating meta-xylidine or pseudo-cumidine with 
sulphur, homologues of primuline are obtained, which, like primuline itself, dye 
cotton without a mordant, and can be diazotised and combined with phenols 
within the fibre. 
It has been long observed by one of us (Green) that the diazo-compound of 
primuline was very sensitive to the action of light, being readily decomposed 
thereby, and losing its property of combining with phenols and amines. Upon 
this fact we have now founded a photographic process, by means of which designs 
can-be produced in fast colours upon cotton, silk, wool, linen, or other fabrics. It 
ean’also be applied to wool, xylonite, celluloid, paper, or to gelatine films upon 
glass, thus affording a very wide range of employment. The process, which is a 
very simple one, merely depends upon the fact that if a material containing diazo- 
tised primuline be exposed to light under a design, those parts which are acted 
upon by light will be decomposed, whilst the parts protected from the light will 
1 A. G. Green, Journ. Soc. Uhem. Ind. 1888, p. 179. 
? A. G. Green, Journ. Chem. Soc. 1889, p. 227; Ber. 22, 968; P. Jacobsen, Ber. 
22, 330; L. Gattermann, Ber. 22, 422+ W. Pfitzinger and L. Gattermann, Ber. 22, 
1063. 
