356 Method of preparing Inks, &c. 
them, but produces by its action a modification of the coe 
lour, they are exceedingly proper for this purpofe. As none 
of thefe, however, were found entirely black, I was obliged 
to employ fome mineral body which might be black and 
yet hold a great deal of oxygen. The moft part of the me- 
" tallic oxyds of a black colour contain very little oxygen, ex- 
cept that of manganefe, which contains a great deal. I made 
choice therefore of this oxyd, and found, after repeated ex- 
periments, that it anfwered the intended purpefe. 
The oxy-muriatic acid diffolves all metals in a metallic 
form as well as metallic calces combined with a {mall quan- 
tity of oxygen, but not thofe which contain a great deal, as 
it has itfelf an excefs of it. It is therefore capable, 
1. Of diffolving metals in a metallic ftate, as the metals 
take up its fuperfluous oxygen, by which, as is well known, 
they become foluble in acids. 
2. Such metallic oxyds as contain little oxygen are capable 
of abftraGing it from acids, and they then diffolve in the 
acids, which then contain lefs oxygen, 
The grounds which induced me to employ oxyd of man- 
ganefe for preparing an ink capable of withftanding the oxy- 
muriatic acid, were as follows :— 
x, Its black colour; 2. its containing a great quantity of 
oxygen, by which it is infoluble in the muriatic acid; 3. be- 
caufe it poffeffes fo great an affinity for oxygen, that whenever 
it has loft any of its original quantity by being brought to 
a red heat, or expofed to the action of acids, it icamndediately 
draws it ay the atmofphere, and again becomes black. I 
fhall now defcribe the method of preparing this ink :—Boil 
1 oz. of Brazil wood with 12 ozs. of water for a quarter of an 
hour; add 4 0z. of alum: evaporate the whole to 8 ozs., and 
mix with the liquor 1 0z. of exceedingly foft, finely pulverifed 
manganefe, mixed up with 4 oz. of pulverifed gum arabic. 
Brazil wood alone, by mere boiling, gives an ink not al- 
together unfit for ufe. Acids, lefs abundant in oxygen, fuch 
as the nitrous and muriatic acid, naturally exercife amaétion 
on this ink; but as thefe change the paper in a perceptible 
manner, deception is not to be apprehended. xf 
Indigo alfo affords an ink that withftands the muriatic 
acid : 
