CAPTAIN NOBLE AND ME. E. A. ABEL ON EIEED GUNPOWDEE. 
127 
Table XVII. — Showing in terms of the density (1) the tension actually found to exist 
in the bores of guns, (2) the tension which would exist were the gases suffered to 
expand without production of work, (3) the tension calculated upon De Saint- 
Robert’s hypothesis, (4) the tension calculated on Bunsen and Schischkoff’s 
hypothesis. 
Mean, density 
of products of 
combustion. 
Tension observed in 
bore of 18-ton gun 
(pebble powder). 
Tension observed 
where the gases 
expand without 
production of work. 
Tension calculated 
upon 
Count De St.-Robert’s 
hypothesis. 
Tension calculated 
upon Bunsen and 
Schischkoff’s 
hypothesis. 
Tons per 
sq. inch. 
Atmo- 
spheres. 
Tons per 
sq. inch. 
Atmo- 
spheres. 
Tons per 
sq. inch. 
Atmo- 
spheres. 
Tons per 
sq. inch. 
Atmo- 
spheres. 
1-00 
41-48 
6320 
41-48 
6320 
41-48 
6320 
•90 
20-35 
3101 
32*46 
4946 
35*75 
5448 
30-00 
4572 
•80 
17-01 
2590 
25-52 
3889 
30-14 
4593 
21-85 
3330 
•70 
14-03 
2133 
20-02 
3051 
25-08 
3822 
15-85 
2416 
•60 
11-33 
1722 
15-55 
2370 
20-18 
3076 
11-62 
1771 
•50 
8-87 
1352 
11-85 
1806 
15-61 
2378 
7-93 
1209 
•40 
6-65 
1019 
8-73 
1330 
11-40 
1736 
5-30 
808 
•30 
4-67 
722 
6-07 
925 
7-60 
1157 
3-28 
500 
•20 
2-93 
459 
3-77 
574 
4-29 
653 
1-75 
267 
•10 
1-77 
270 
1-61 
246 
•64 
98 
The graphical representation of this Table is given in Plate 23 ; and by examination 
either of the Table or of the Curves, it is obvious that neither formula (16) nor (21) 
gives results which can be taken as at all representing the truth. The values of the 
elastic force, calculated on the assumption that the whole of the products of combustion 
are in the gaseous state, and that the effect on the projectile is produced by such expan- 
sion, are largely in excess of the pressures observed in the gun, and very greatly in 
excess even of the pressures observed when the gases were expanded without production 
of work. On the other hand, the pressures calculated on the assumption that the work 
is caused by the expansion of the permanent gases alone , without addition or subtraction 
of heat, are considerably in defect of those actually observed, and this too, although, no 
allowance is made for the absorption of heat by the gun. 
At an early stage in our researches, when we found, contrary to our expectation, that 
the elastic pressures deduced from experiments in close vessels did not differ greatly 
(where the powder might be considered entirely consumed, or nearly so) from those 
deduced from experiments in the bores of guns themselves, we came to the conclusion 
that this departure from our expectation was probably due to the heat stored up in the 
liquid residue. In fact, instead of the expansion of the permanent gases taking place 
without addition of heat, the residue, in the finely divided state in which it must be on 
the ignition of the charge, may be considered a source of heat of the most perfect 
character, and available for compensating the cooling effect due to the expansion of the 
gases on production of work. 
The question, then, that we now have to consider is — What will be the conditions 
of expansion of the permanent gases when dilating in the bore of a gun and drawing 
