172 ON THE MANUFACTURE OF PRUSSIATE OF POTASH. 
Some manufacturers use thrice the weight of material to 
the potash, but this is too large a proportion, as the mass 
becomes so stiff that the animal matter cannot be mixed 
in rapidly enough lo save it from burning to waste. The 
amount of material that can be used to advantage is indi- 
cated by the consistence of the pasty mass which should 
always be soft enough to flow readily after the poker. The 
thickening of the mass is owing to the deposition of carbon 
by decomposition of the animal material, and hence those 
kinds which contain least carbon can be employed in the 
largest proportion to the potash. Thus a greater weight of 
horn can be used than of leather, for the same wdght of 
potash. 
The material should be perfectly dry, as, if damp, it chills 
the furnace, and causes great loss of product. 
Horn yields eleven to twelve per cent, of prussiate, dried 
blood, and hoofs ten to eleven per cent, greaves about ten 
per cent., leather five or six per cent , and rags from four 
to ten per cent., according as they are all woollen, or more 
or less mixed with cotton, the latter substance, of course, 
not producing any prussiate. Another practical point to 
be attended lo, is the fact that heavy material is more pro- 
ductive than light of the same kind ; as, for instance, horn 
pieces are much to be preferred to the shavings, on account 
of mixing more readily into the fused potash, the light ma- 
terial burning to waste on the surface of the alkali before it 
can be mixed in. 
The furnace is worked night and day by relays of work- 
men, and when in good working order turns out fifty-four 
to sixty cakes weekly. Each cake yields from ten to 
eighteen lbs. of refined prussiate, according to the quality 
and quantity of the material employed, the skill and faithful- 
ness of the workmen, and the greater or less perfection of 
manipulation. 
A prussiate furnace, if working properly, seldom lasts 
more than two months ; the iron shell having to be renewed. 
