Mortar . 
271 
For Stucco , bone ashes well burnt and sifted, in the 
proportion of from one half to one fourth of the lime, is , 
an addition useful to prevent the cement from cracking, 
without impairing its other good qualities ; and this whe- 
ther for inside or outside work. For the latter the pro- 
portion ought not to be of bone ashes more than one 
fourth. 
The method of making bone ashes is as follows : I take 
it from page 172 of Higgins on Cements. 
“ 1 will premise a sketch of the most profitable pro- 
cesses by which they are prepared, at a moderate price 
not much exceeding that of good stone lime. 
The bones collected in great cities, are broken to small 
fragments in a mill, and boiled in water, in order to 
extricate and save the oil of them. They are then put 
into a large iron still, through an aperture which is stop- 
ped up closely after the charge is made. The still, 
which opens into an apparatus of refrigeratory vessels, 
is heated gradually to redness, until all the volatile alkali, 
commonly called spirit and salt of hartshorn, is expelled 
from them, together with empyreumatic oil, water, and 
certain elastic invisible fluids : the alkali, being the only 
valuable article amongst these, is retained and condensed 
in the refrigeratory tubes and vessels with all possible care, 
whilst the elastic fluids, lest they should burst the vessels, 
are suffered to escape in places distant from the fire or the 
flame of candles, because they are combustible, and if 
they catch fire whilst air remains in the condensing ves- 
sels, explode like gunpowder. 
The bones thus heated without being exposed to the 
air, are charred to blackness, but still remain combusti- 
ble. When they are required in this state, the iron still 
is kept closed until they cool, and then the blackest of 
them are ground to fine powder, which is used as a sub- 
