18 = On the Manufacture and Use of Animal Charcoal 
ing; but, since the discovery of the properties of charcoal as a 
purifier and clarifier, they make use of it in sugar-refineries, la- 
boratories, and stills, as well as for purifying oil, &e. Many 
manufactories have been established, and the preparation of bone- 
black is now become a separate art, of interesting consideration. 
There are many manufacturers of animal charcoal in Paris. 
Their process is very simple. Some, after filling a number of 
earthen or iron pots with broken bones, lute on the cover with 
potters’ earth, then pile one over the other in a potters’ kiln, 
which is heated with wood or pit-coal: when the degree of 
heat becomes sufficient to decompose the gelatine and oil of the 
‘bones, the luting cracks in small fissures, and gives issue to the 
carbonized hydrogen gas, which escapes from the furnace by se~ 
veral small apertures made for the purpose, one above another, 
and on reaching the atmospheric air becomes ignited, and is con- 
sumed. When this flame goes out, the combustion is completed. 
In England and France, other manufacturers distil bones in cy- 
linders of cast-iron that run through a great fireplace, or in iron 
alembics ; but in these manufactories the bone-black is looked 
upon as of only secondary importance; for it is for the purpose 
of making carbonate, sulphate, and muriate of ammonia, that 
they generally distil bones. Without that, the black would come 
too dear, and be seldom demanded, notwithstanding its utility. 
In this process, the form of the vessel is of small importance, 
provided it be well closed: the great point is to make use of the 
least fuel possible, and apply the heat equally every where. When 
this is done on a large scale, the most convenient furnaces are 
those employed in London, and of late in Paris, for the gas-lights. 
With this apparatus, you have two choices to make ; the first, 
to make use of the gas for lighting, and it renders a whiter and 
more lively flame than the gas of mineral coal; the second is the 
conveniency of burning this gas in the fire-place itself, and thus 
greatly ceconomizing fuel *, If the gas is to be employed as fuel, 
the iron cylinders or cucurbits should be so disposed as to admit 
of their contents being easily renewed. There are several means 
for this purpose; but the simplest is to place a disk of strong 
plate-iron in the bottom of each cylinder, riveted to one or two 
* We here omit a few lines in which the author recommends, if the gas 
is to be employed as fuel, “ to adapt two diaphragms of wire-gauze to the 
funnel which conducts the gas under the fire-place, to prevent explosions.” 
It is plain, from his recommending this, that he has never tried any ex- 
periments respecting the combustion of hydrogen, or hydro-carbonic gas, 
neither of which can explode till after they have been mixed with the atmo- 
spheric air. He has been thinking of Sir H. Davy’s lamp, where it is ne- 
cessary to preyent the passage of combustion, the surrounding gas being 
ina mixed state, ready for explosion;—and so in Dr. Clark’s lamp, in which 
the gas in the reservoir is in a like condition. 
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