176 
MISCELLANEA. 
facture of blacking, or phosphorus for the manufacture of 
lucifer-matches ; or we may use it for manure, or as an ele- 
ment in the manufacture of earthenware ; and finally we may 
distil the entire bone and get an ivory-black fit for making 
sugar white, whilst another substance is at the same time 
obtained, from which smelling-salts are made. Thus the 
bones thrown to the dogs, in this utilitarian age may come 
back to us again on our dinner-table, as a part of our dress, 
as the medium of our politeness, as a means of washing our 
hands, lighting our fires, and blacking our boots ; and, finally, 
as the contents of that all-important article — a lady’s smelling 
bottle. We will suppose we have a quantity of old woollen rags, 
too bad to be used for any of the purposes above mentioned, 
and animal offal, such as comb-makers’ shavings, pigs’ toes, 
dried blood, & c, ; if we calcine these substances for a consi- 
derable time with pearlash or carbonate of potash (which is the 
principal ingredient in the ash left by trees when burned), and 
some iron filings, in an egg-shaped iron pot, stirring it from time 
to time, we shall obtain a mass which, when boiled with water, 
the insoluble impurities removed, and the liquid evaporated, 
will yield beautiful yellow crystals of a substance known as 
prussiate of potash. But what is the use of these yellow 
crystals ? Distilled with oil of vitriol, the salt is decomposed, 
and prussic acid formed, the most violent of all poisons. 
Prussic acid made from woollen rags, blood, and pigs’ toes ! 
This acid, in a peculiar state of combination with iron, forms 
what is called ferro-prussic or ferro-cyanic acid, which, com- 
bined with potash, forms the yellow salt of which we are 
writing, and which, although it maybe said to contain prussic 
acid, is nevertheless quite innocuous. If, instead of distilling 
it with sulphuric acid, we fuse it at a bright red heat, the iron 
separates, and we get a white salt, containing prussic acid in 
combination with potash, and which is, to a great extent, 
poisonous. Thus, a little iron alone is sufficient to alter all 
the properties of this curious substance. The white salt 
made in this way is largely employed in preparing solutions 
of gold and silver for electro-plating ; and the greater part of 
the silver and gold with which the various electro-plated 
articles in common use have been coated, has existed at one 
period in combination with this white substance. Another 
use of this yellow salt is to produce prussian blue, which is 
formed by adding to a solution of it in water some sulphate 
of iron or green copperas, wffien the ferro-prussic acid w ill 
part company with the potash ; the latter will unite with the 
sulphuric acid of the copperas, leaving the iron of the latter 
to unite with the ferro-prussic acid to form the prussian blue. 
