Thus a
combination of a red, a yellow, and a blue colouring matter, when
concentrated enough, will not let any light pass through it, and can
thus be used for the production of blacks, and this property is made use
of in dyeing. And now we see why a little yellow dye is added to our
coal-tar black. A purplish shade would else be produced; the yellow used
is a colour complementary to that purple, and it absorbs just those blue
and purple rays of the spectrum necessary to illuminate by radiation
that purple, and _vice versa_; both yellow and purple therefore
disappear. In like manner, had the black been of a greenish shade, I
should have added Croceine Orange, which on the fabric would absorb just
those green and bluish rays of light necessary to radiate from and
illumine that greenish part, and the greenish part would do the like by
the orange rays; the effects would be neutralised, and all would fall
together into black.
THE END.
INDEX
Acetone, 64
Acid, boric. _See_ Boric acid.
" carbolic.
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