184 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. [September s, 1870. 
the carbonic acid evolved in fermentation. Conse¬ 
quently,— 
Units of heat. 
The alcohol from 171 grm. sugar gives 017,818 
171 grams sugar give in fermentation 22,743 
Total. 640,501 
According to Frankland’s determination, 
however,—171 grams of sugar give 572,508 
Or less by. 68,053 
Without taking into account the combustion of other 
products of fermentation, which would have given 
from 8000 to 10,000 units of heat, sugar gives 
nearly one-eighth more heat than Franldand’s calcu¬ 
lation indicates, when it is burnt otherwise than in 
the direct way"; if we suppose alcohol to be oxidized 
at a low temperature, first to aldehyde, then to acetic 
acid, formic acid and lastly to carbonic acid, it is 
possible that other numerical results might be ob¬ 
tained for its heat of combustion. 
In the determination of heat of combustion much 
depends on the work done in combustion; if part of 
the heat be expended in overcoming resistances, that 
part does not appear as sensible heat. 
The simple difference of density in the diamond 
makes the form of carbon less combustible than 
charcoal, and it gives rise to a difference in the heat 
of combustion. The calorific power of diamond is 
less than that of charcoal by 285 units [of heat.* 
This fact is accounted for by the assumption that the 
diamond hi crystallizing has lost heat, which again 
becomes latent in combustion ; moreover, since cohe¬ 
sion is a resistance to be overcome in the combina¬ 
tion of carbon with oxygen, another portion of the 
heat generated is expended hi overcoming that re¬ 
sistance, therefore less heat becomes sensible. 
The determinations of the heat of combustion for 
various lands of food materials by Frankland are 
certainly applicable for estimating the value those 
materials would have as fuel for generating steam ; 
but I am of opinion that his numbers have no special 
significance as expressing the calorific power of food 
materials hi the living body. 
This, is more especially the case in regard to the 
determinations of the heat of combustion of nitro¬ 
genous constituents of the body, or the albuminates 
in articles of food, and in regard to the inferences 
Frankland has drawn from those determinations as 
to the value of albuminates as a source of power. 
These materials are not combustible in the ordi¬ 
nary sense of the term, neither are they burnt hi the 
animal body any more than sugar as such is burnt; 
in regard, to combustibility and their power of com¬ 
bining with oxygen, they are among organic sub¬ 
stances analogous to gold and silver among inorganic 
substances. 
As to tlieir combustibility, the chemist knows 
well how difficult it is to burn organic substances 
that are rich in albuminates. Even at a red heat 
maintained for hours or days some portion of nitro¬ 
genous carbon remains imburnt. The same difficulty 
is experienced also with urea and uric acid salts. 
Most nitrogen compounds that are not gaseous 
possess this peculiarity. There is certainly no more 
inflammable or more combustible substances than 
hydrogen and phosphorus, but then- compounds with 
nitrogen are entirely uninflammable; for instance 
ammonia, though it contains half its volume more 
hydrogen than ordinary hydrogen gas does. 
The non-inflammability of these substances ob¬ 
viously is due to the resistance offered by the nitro¬ 
gen they contain to the action of oxygen. Taking 
heat also into account, it appears that according to 
the determinations of Favre and Silbermann, 1 
gram of hydrogen in combining with nitrogen to form 
ammonia developes 7576 units of heat, or nearly as 
much as is developed in the combustion of 1 gram 
of carbon to carbonic acid. It must probably be as¬ 
sumed that in the combustion of 5'66 grams of am¬ 
monia, containing 1 gram of hydrogen, an equal 
quantity of heat would be expended in the work of 
combustion. Perhaps this may be regarded as a 
reason why ammonia burns with so much difficulty 
but it is not the only reason. Very much appears 
to depend on external conditions; if they facilitate 
the oxidation of nitrogen, as is the case in mixtures 
of decaying materials with alkaline bases, then the 
hydrogen of ammonia burns with great readiness. 
In cyanogen and paracyanogen we have two com¬ 
pounds of nitrogen and carbon identical in composi¬ 
tion, but presenting a remarkable difference in re¬ 
gard to combustibility, cyanogen being readily com¬ 
bustible, while paracyanogen burns with great diffi¬ 
culty. 
Observation shows that 1 gram of carbon in cya¬ 
nogen developes by combustion 43 per cent, more 
heat* than 1 gram of carbon does when burnt by itself. 
Evidently, therefore, this surplus heat must be 
rendered latent in the formation of cyanogen, and in I 
fact in the conversion of cyanide of silver into the 
paracyanide so much heat is developed that the 
mass becomes red-hot. If the combustibility of cya¬ 
nogen be due to the latent heat it contains, still that 
does not explain why the carbon in paracyanogen 
appears to have lost its affinity for oxygen to such a 
great extent. 
This consideration of the behaviour of some nitro¬ 
genous substances may suffice to show that it is not 
admissible to estimate their efficacy as sources of 
power according to the amount of heat they may 
develope by direct combustion. 
We may suppose the possibility of maintaining a 
machine in a state of work by bringing the vapour 
of chloride of nitrogen in contact with phosphorus 
in a vessel, and yet it would be next to impossible 
to determine the work done directly in heat units,, 
for neither chlorine nor nitrogen are combustible 
substances in the ordinary sense of the term. 
Chloride of nitrogen is formed by the action of 
chlorine on ammonia; if there be excess of ammonia 
no chloride of nitrogen is formed, but the chlorine 
then decomposes the ammonia with considerable 
evolution of heat. In the absence of free ammonia 
chloride of nitrogen is formed without any rise of 
temperature. It is evident, then, that all the heat 
developed in the former case is in the latter case 
rendered latent in the chloride of nitrogen; how¬ 
ever, in the decomposition of this substance the 
latent heat does not reappear as heat, but as motive 
force. 
There are many cases in which mechanical or 
motive effects are produced by some internal or 
molecular motion. The magnitude of the effect in 
these cases depends upon the tension in which the 
parts exist in regard to one another. 
* Favre and Silbermann. 
* 11,260 beat units. 
