CAPTAIN NOBLE AND MR. F. A. ABEL ON FIRED GUNPOWDER. 
125 
to correct Hutton’s assumption ; and the question of the pressure exercised and work 
performed by gunpowder in the bore of a gun has been examined both by Bunsen and 
Schischkoff, and by the Count de Saint-Robert *. 
De Saint-Robert, like Hutton, supposed that the whole of the products of explosion 
were, on ignition, in a gaseous state, and that hence the relation between the pressure 
and the volume of the products followed from the well-known law connecting the tension 
and volume of permanent gases. 
Bunsen and Schischkoff, on the other hand, who, like ourselves, have arrived at the 
conclusion that at the moment of explosion a large part of the products is not in the 
gaseous state, have deduced the total work which gunpowder is capable of performing, 
on the assumption that the work on the projectile is effected by the expansion of the 
permanent gases alone, without addition or subtraction of heat, and that, in fact, the 
non-gaseous products play no part in the expansion. 
Sufficient data were not at the command of either of the authorities we have named 
to enable them adequately to test their theories ; and we propose in the first place, with 
the data at our disposal, to compare their hypotheses with actual facts, by computing 
the tensions for different volumes and comparing the calculated results both with the 
tensions in a close vessel and with those derived from actual experiments in the bores 
of guns. 
Assuming, in the first place, with De Saint-Robert, that the whole of the products 
are in the gaseous form, — 
Let^? be the value of the elastic pressure of the permanent gases generated by the 
combustion of the powder corresponding to any volume v, and letp 0 , v 0 be the known 
initial values of and v. Let also C p be the specific heat of these gases at constant 
pressure, and C„ be the specific heat at constant volume. Then, from the well-known 
relation existing between ]) and v, where a permanent gas is permitted to expand in a 
vessel impervious to heat, we have 
and this equation, upon De Saint-Robert’s hypothesis, expresses the relation between 
the tension of the gases and the volume occupied by them in the bore of a gun. 
Taking^ from Table VIII. at 41 ‘477 tons per square inch, and assuming at unity 
the space v 0 occupied by the charge when at a gravimetric density of 1, taking, further, 
0 
the value of 0 £ =1 , 41 as computed by De Saint-Robert, equation (15) becomes 
^ = 41-477 Q 1 ' 41 (16) 
If we now take Bunsen and Schischkoff’s view, that a portion only of the products 
is in the form of permanent gases, and that they expand without addition or subtraction 
* Traite de Thermodynamique, p. 154. 
