264 Scientific Proceedings, Royal Dublin Society. 
chemically on each other, and produce new bodies, which may be 
granular or of a newcolour. Ordinarily, yellow and blue make 
green: thus, indigo carmine, when mixed with either picric acid, 
napthal yellow, or tartrazene yellow will produce various shades 
of green; but if methylene blue be mixed with the same yellows, 
a purple colour is produced with picric acid, an orange with 
napthal yellow, and a green with tartrazene yellow. 
The colours which I have found satisfactory both as to mix- 
tures and ease of laying on evenly are—eosin, tartrazene yellow, 
vesuvin, indigo carmine—with soluble blue as a useful alternative 
for the last for bright green, when mixed with tartrazene yellow. 
Methylene blue, methyl violet, and iodine green did not appear to 
be satisfactory colours. 
As some of the anilin dyes are liable to fade on exposure to 
light, I painted a test slide with parallel lines of the colours just 
mentioned and others, and having covered one half of the plate 
with black paper, placed it in a lantern illuminated with a Brockie- 
Pell are lamp. The light was maintained at intervals, as was 
found convenient, until a total of five hours had been reached, 
when it was found that eosin, methyl violet, and iodine green faded 
most; others slightly, and tartrazene yellow and indigo carmine 
very little, if at all. Subsequently, a similar plate of eosin, atlas 
scarlet, and two varieties of erythrosin was illuminated for five 
hours before the arc-light, in the hope that one of them would 
prove more permanent than eosin. They were, however, very 
similar in their permanence. 
One sample of erythrosin, obtained from Schuchardt of Gorlitz, 
seemed a trifle better than the other make of erythrosin and the 
other colours. ; 
Itis difficult to find a dye so brilliant as eosin, even erythrosin 
being much more purple ; so I have recommended eosin as one of 
my selected colours, notwithstanding its defects ; it must, there- 
fore, be applied a little more intensely, if the slide is intended for 
much use. Very faint pinks will fade completely ina few minutes 
in the lantern, while, on the other hand, I have slides in use for 
years which have been rather strongly coloured, and show no 
appreciable amount of fading yet. 
Coloured outline diagrams may be made on clear glass by using, 
with an ordinary pen, solutions of the dyes which have been 
