456 
Prussian Blue . 
for linen already whitened and made up, as shirts, table 
linen, &c. a solution of iron in nitrous acid thickened 
with gum arabic, is just as good : for although it may 
be discharged by the skilful application of acids, it will 
never wash out. Or a few drops of the nitrat of silver 
may be added to the nitrat of iron. The nitrat of iron 
does not require the previous use of the solution of pearl 
ash, as it is not so corrosive when fully saturated, as the 
nitrat of silver. If linen be marked with well- dyed blue 
thread, or with thread dyed a true turkey-red, no wash- 
ing will discharge the colour. 
PRUSSIAN BLUE. 
The methods of making this pigment are kept secret 
in England and this country, I shall therefore present my 
notes on the subject with remarks on the processes I have 
collected. 
I have repeatedly made it myself thus. Dry thorough- 
ly in an iron vessel and powder grossly, any quantity of 
fresh blood. Dry thoroughly and powder also a quan- 
tity of pearl ash equal to the powdered blood. Mix them, 
and calcine them in a low red heat in a crucible with a 
loose cover until all smoke and flame ceases : then make 
the cover fit close, and calcine in a full red or nearly white 
heat for half an hour. The crucible should not be more 
than two thirds full, as the mixture is apt to swell. Emp- 
ty the contents of the crucible into warm water in the pro- 
portion of a quart to four oz. of the mixture. Pour 
on again as much warm water : mix and filter the solu- 
tions. Dissolve of sulphat of iron (green vitriol) and of 
alum, of each a quantity equal to one half of the pearl ash 
employed. Pour the solution of alum and green vitriol 
mixt together, gradually into the solution of blood and 
alkali : both solutions are better for being warm, but not 
boiling hot. Stir it well. Let the sediment settle* It 
