VEGETABLE DYES 117 
intimate study of the dye plant ‘itself—its physiology ; 
the production and maintenance of good, pure strain 
seed; the best methods of dye development and ex- 
traction, etc. The importance of this kind of work is 
amply ilustrated by recent work on indigo. If only 
the processes leading to dye production in the plint 
were really understood, there is very little doubt that 
the yield of dye could be greatly increased by suitably 
modifying the conditions of cultivation. 
There is still another side of the dyeing process, 
which is of general application, but affects plant dyes 
most especially, and this is the potentialities of new 
mordants. The periodic table positively bristles with 
elements, closely allied to iron and chromium, ampho- 
teric electrolytes, having the chemical properties 
appropriate to a mordant, e.g. nickel, cobalt, molyb- 
denum, tungsten, uranium, titanium, bismuth, gold, 
platinum, and all the rare earths. 
Now it is of the first importance, if a plant dye is to 
be the standard thing for a given colour or colours, that 
exactly the right mordant should be used to bring out 
its best qualities. Further, the modification in tone 
introduced by a change in mordant often increases the 
colour range of a given dye quite appreciably. This 
can easily be illustrated by dyeing with alizarin on 
some of these theoretical mordants. Most of the colours 
produced fall within the usual range, but nickel gives 
old gold, cobalt bright yellow, bismuth crimson, 
while uranium gives a good heavy black; these are, in 
different directions, outside its. usual range. Some of 
these mordants, especially the heavier metals in the 
chromium group—molybdenum and uranium—have the 
