146 INDELIBLE WRITING INKS; 
thus becomes more black and less soluble. By adding 
sugar and other substances to this ink, it is used for copy- 
ing purposes, being thereby rendered more soluble, but is 
then far less permanent, as I have had the opportunity of 
proving by examining letters in copying books, kindly shown 
me by the Hon. A. C. Gregory, C.M.G., F.R.G.S., some of 
which, having been copied in 1865, are barely legible, 
although he has tried to renovate them by several chemical 
processes. This fact seems to thoroughly prove the im- 
portance of devising another mode of copying important 
documents. 
Blue inks are generally made of Prussian blue. 
Stephens’s unchangeable blue ink is made by dissolving this 
blue in an aqueous solution of oxalic acid. Ink made from 
this blue, although not affected much by the physical causes 
which so injure black ink, will, when exposed to a strong 
light, fade; but, on being again placed in a dark place, 
resume nearly its original colour. 
Red inks are made of logwood or cochineal and chloride 
of tin. Alum used instead of this chloride, makes the ink 
more of the colour of lake. 
All other fancy coloured inks are usually made of aniline 
dyes, and are extremely evanescent. 
The following black ink has been recommended as a 
very permanent one, and not obtainable by the interaction of 
chemical substances, viz., twenty-four pounds of Frankfurt 
black (which is said to be a carbon obtained from grape 
and vine lees, peach kernels, and bone shavings) ground 
with twenty pounds of gum-arabic to sixty gallons of water, 
adding four pounds of oxalic acid and a solution of cochi- 
neal, sulphate of indigo, or Prussian blue. These colours 
are used to produce the required tint. 
With reference to Indian ink, of which carbon is the chief 
constituent, it may be well to notice some of its principal 
qualities. It is not generally known, perhaps, by the public, 
that it is the best known marking ink for linen and other 
fabrics, not being liable to turn brown or yellow, as all 
other marking inks seem to do. The draftsmen in the Sur- 
veyor-General’s office here have had long experience on 
this point, for it has been their habit to mark the towels 
used there with this ink. Now, of course, such articles 
