782 REPORT—1890, 
remain unaltered, and consequently, on subsequent development with a phenol or 
amine, will produce colours, whilst the decomposed portions will not. The details 
will of course depend somewhat upon the material to be treated. As an instance 
we may take the production of a design upon cotton cloth, cotton velveteen, &c. 
The material is first dyed with primuline from a hot bath containing common salt 
until the required depth is obtained. It is then washed and diazotised by being 
immersed for } minute in a cold bath containing about }p.c. of sodium nitrite, 
and strongly acidified with sulphuric or hydrochloric acid. The material is washed 
again, and exposed damp (or if preferred after having been dried in the dark) to 
the action of light beneath leaves, ferns, flowers, or other natural objects, or 
beneath glass or transparent paper upon which may be painted or printed any 
design which it is required to copy. Wither the are electric light or daylight may 
be employed ; in the latter case the time of exposure will of course vary with the 
intensity of the light; under 4 minute is required in bright sunshine and nearly 
3 hour in very dark cloudy weather. When the decomposition is complete, which 
may be readily ascertained by means of a test slip exposed simultaneously, the 
material is removed from the light and either passed into the developing bath at 
once, or is kept in the dark until it is convenient to develop it. The developing 
bath consists of a weak solution (4 to 3 p.c.) of a phenol or amine made suitably 
alkaline or acid, the phenol or amine employed depending upon the colour in which 
it is required to produce the design, thus :— 
For ved .  . an alkaline solution of 8-naphthol. 
» maroon . an alkaline solution of B-naphthol-di-sulphonic acid, 
» yellow . an alkaline solution of phenol. 
» orange . an alkaline solution of resorcin. 
y, brown . asolution of phenylene diamine hydrochloride, 
yy» purple . asolution of a-naphthylamine hydrochloride. 
If it is required to produce the design in two or more colours, the respective de- 
velopers, suitably thickened with starch, may be applied locally by means of a 
brush or pad. After development the material is thoroughly washed and requires 
no further fixing. 
Linen, silk, and wool are treated in exactly the same way. Paper for copying 
drawings, &c., is coated on the surface with primuline by means of a brush or 
roller. For the production of gelatine films upon glass the primuline is incor- 
porated with the gelatine before being applied to the glass. 
In place of ordinary primuline the homologues already mentioned may be used. 
For silk and wool the primuline may be replaced by dehydrothiotoluidine-sulphonic 
acid, by means of which colourless backgrounds may be obtained. 
Concerning the reaction which occurs when the diazo-primuline or the diazo- 
dehydrothiotoluidine is decomposed by light, we cannot at present say anything 
definite, except that the diazo group is completely destroyed, for on treatment with 
sodium hydrosulphite (true hyposulphite) it cannot be converted into the amido- 
group (re-forming primuline or dehydrothiotoluidine). The reaction may consist 
in a replacement of the N, group by OH or by H, or may be even more complex. 
Although we cannot affirm that this reaction to light is a property of the diazo- 
compounds of this group of bodies only, yet it is certain that they possess an 
extreme susceptibility to light far greater than that of other diazo-compounds, 
whilst at the same time they are far more stable to heat. It is thus possible that 
this property may depend in some way upon the sulphur which they contain. 
7. Fast and Fugitive Dyes.1 By Professor J. J. HuMMEL. 
The influence of light on dyed colours was considered, and after explaining 
that, according to Chevreul, the fading of such colours is due to the combined action 
of light, atmospheric oxygen, and moisture, the results of experiments made in the 
Dyeing Department of the Yorkshire College, Leeds, were briefly given. The 
1 In extenso vide Textile Manufacturer, 1890, vol. xvi. p. 506. 
