820 
The Manufacture of Iron in 
atmospheric nitrogen. Such at least was the doctrine taught by 
Liebig, who believed that ammonia or its compounds were the 
vehicles wliicli conveyed this form of nourishment through the 
vegetable to the animal world. As in the case of carbon, so with 
ammonia ; we have also to look to the atmosphere for our origi- 
nal supply of this alkali, in which, however, it exists as a mere 
trace — one part in one million of air. Liebig himself estimated 
that if it were all collected at the sea-level and had a density cori’e- 
sponding to the atmospheric pressure there, it would form a stratum 
less than a quarter of an inch in depth. This ammoniacal nitrogen, 
partly in the form of nitrite or nitrate or carbonate of ammonium, is 
brought down by rain and received into the plant through its roots 
from the soil. This means decomposition of the alkali into nitrogen 
and hydrogen ; and although fresh ammonia is generated by vege- 
tables and animals during their decay, yet, in a densely populated 
country like ours, and with our sanitary arrangements upon their 
present footing, the waste of assimilable nitrogen is enormous, and 
appears to require being compensated for from other sources than 
those which have just been enumerated. 
Ammonia and its compounds are put to other purposes than the 
stimulation of vegetable life, but the ammonia contained in the 
atmosphere is too diluted to be of any use in the arts. A very 
small quantity, and very irregular in its occurrence, in the form of 
sal-ammoniac (or ammonium-chloride), is occasionally met with in 
volcanic regions. Chaptal, the F rench chemist, who wrote near the 
end of the last century, states that all the sal-ammoniac then 
I’equired in commerce was made in Egypt from the distillation of 
camels’ dung with common salt, the fuel used being also the dung 
after it had been dried. Animal matters with salt were also exposed 
at a subsequent date to a high temperature in this countiy, and the 
resulting ammoniacal salt was collected and supplied, of course, at 
very high price. So late as a quarter of a century ago it was sold 
at iQl. or 50/. per ton, the value now being about 35/. It is clear 
that all these processes must have been attended with consider- 
able exj^ense, quite incompatible with the use of ammonia as a 
medium for enriching the soil. 
If we descend through the crust of the earth until we reach 
those subterranean forests which now form our coal, and if we 
examine their composition, we find that countless ages ago nitrogen 
was assimilated by vegetation as it is at the present day, and is to 
be found in pretty much the same quantity as exists in the plants 
growing in our own time. When coal is burnt in an open fire, all 
the hydrogen it contains, including that in the ammonia, is con- 
verted into water, leaving the nitrogen to escape as such, with 
the formation of little or no ammonia. If, however, the coal is 
heated in a closed vessel with salt, air being excluded, the volatile 
carbon and its associated hydrogen pass off as tarry matter, and 
the nitrogen, taking up hydrogen, is carried over in the form of the 
precious ammoniacal alkali so much wanted. 
Coal, up to the earlier part of the present century, was 
