148 INDELIBLE WRITING INKS; 
be discovered for preparing it mixed and bottled ready 
for use, the same as our ordinary inks. This seems 
to be quite feasible, and, if not, would it not be 
preferable to spend a few minutes in preparing the ink 
before writing valuable documents which are intended to 
be handed down to future generations, instead of writing 
with an ink which is so fugacious, as the modern ink 
undoubtedly is? It seems surprising that this matter has 
been so long neglected by our savants. 
The more compound the inks are, the more likely are 
they to fade, as is proved by the copying inks, which fade 
far sooner than those composed of fewer elements; the 
extraneous substances introduced, such as sugar, gums, &c., 
causing a greater chemical action to take place. 
To test inks as to their permanency, drop a little hydro- 
chloric acid upon them. If they remain black, you may 
consider they are not liable to fade. The ordinary blue- 
black ink will lose its blackness in a very short time, still 
retaining a little of the blue colour; red ink will fade 
entirely away. The well known experiment may be tried 
of sprinkling a few drops of the acid on a black cloth coat, 
which is dyed with a similar material to black ink; in a 
short time the spots will appear of a bright red colour. 
The black may be restored by applying a solution of sulphate 
of iron. 
Although our written documents may fade entirely away 
in a comparatively short space of time, there will be a large 
proportion of our valuable literature preserved in the shape 
of books, thanks to our printing press, as the black print- 
ing ink used in printing is chiefly composed of a carbon 
pigment. But many of the colours now used in printing 
are evanescent, notably violets, carmines, lakes, most 
madders, and perhaps all aniline colours. Those more 
durable are ultramarine blue, greens, chrome yellows, | 
brown and yellow ochres, Chinese vermillion, and rose 
madder, but none of these colours are so vivid as the 
aniline ones. 
The subject of photographic prints may not be out of place 
here, as being somewhat connected with the subject of inks. 
It is well known by many that the ordinary silver prints 
will gradually fade away. It may be well to state (for the 
