PATENT INKS, AND SALTS OF GOLD, 
67 
iodide of potassium solution is directed to be used under the 
second head of this specification. 
Black Writing Ink. 
5th. I manufacture a very superior black writing ink, by 
adding to gall ink of a good quality soluble Prussian blue, 
described under the first head of this specification. The 
addition of this Prussian blue makes the ink, which was 
already proof against alkalies, equally proof against acids, 
and forms a writing fluid which cannot be erased from 
paper by any common method of fraudulent obliteration, 
without the destruction of the paper. 
Red Writing Ink. ' 
6th. I manufacture, in manner following, a red writing 
ink, which is greatly superior to the common solutions from 
peach-wood and Brazil-wood, not only in permanent bril- 
liancy of colour, but also in its freedom from acid, and con- 
sequent fitness for use with steel pens. I first boil cochineal 
repeatedly in successive quantities of pure water, till it 
ceases, or nearly so, to give out any colouring matter. I 
then boil it in water containing liquor ammonise, which 
combines after the manner of an alkali with an acid, with 
the residue of colouring matter, and leaves the insect matter 
nearly white. The liquid products of these successive boil- 
ings are then thrown together into an earthenware vessel, 
and in order to get rid of a peculiar element or principle 
still combined with the colouring matter, and which has a 
great affinity for iron, I precipitate the colouring matter 
with ammonio-bichloride of tin. The precipitate is after- 
wards dissolved in ammonia, and protiodide of tin added, 
till a sufficient degree of brilliancy of colour is obtained, 
which completes the process, water being added ad libitum, 
according to the degree of body desired to be given to the 
ink. 
