Prussian Blue . 
457 
will be of a dirty greenish colour : wash it. Then digest 
it for 2 or 3 days in diluted muriatic acid, (spirit of salt 
one part, water two parts.) The colour by this means 
gradually becomes blue, because the muriatic acid dis- 
solves the yellow oxyd of iron which is not combined 
with the prussic acid. Wash it repeatedly. Dry it on 
chalk stones, paper, linen, or any other mode of draining 
off the water. Spread it thin to expose it to the air, 
I have kept the lixivium of blood and alkali (prussiat of 
potash) for a year and a half in bottles, and used it to make 
prussian blue with equal success as at first. Chippings 
of hoofs answer equally well with blood. 
The more alum is put in, the more the colour is dilu- 
ted, but it seems to be of use also, to save the muriatic 
acid. 
In Philadelphia, hoofs and refuse cuttings of leather are 
Calcined together with potash in a large iron vessel, but I 
do not know the proportions. My own experiments per- 
suade me that more than one part or at the most, one part 
and a half of potash, to one part of animal charcoal by 
weight, is too much : but I believe the common propor- 
tion now is one part and a half of potash. The vessel in 
which the mixture of solutions is made, should be large, 
and the solution of copperas and alum gradually added, 
on account of the effervescence. 
Another. “ Heat the iron calciner red*hot; then put into 
it one hundred weight of horns and 25 ibs. of pot or pearl 
ash, the horns will immediately begin to smoke violently ; 
this inconvenience is considerably lessened by setting fire 
to the smoke with a bit of lighted paper, it will continue 
to burn at the mouth of the vessel for some hours. The 
fire is to be kept up or rather increased. In about two 
hours time, the horns will be considerably calcined, and 
must then be frequently stirred with an iron poker : af* 
tgr this has been continued for a length of time which Is 
