1892.] Pressure developed l>y some New Explosives. 123 



we reduced the continuous spectrum sufficiently to enable us to 

 observe any fairly strong rays which might be peculiar to the flame. 

 In the visible part of the spectrum the three well-known rays of zinc 

 in the blue X4812, 4721, and 4681 were easily seen. Photographs of 

 the more refrangible part of the spectrum showed no trace of the 

 ultra-violet lines of zinc ; no more, in fact, than the flames of hydro- 

 carbons usually show. Nor did there appear to be any rays from the 

 base of the flame other than those seen in hydrocarbon flames in 

 general. In our observations on explosions (Zoc. cit.) we did not find 

 that a zinc lining to the tube in which the oxy-hydrogen gas was 

 exploded brought out any zinc line, either in the visible or ultra- 

 violet part of the spectrum. The flame of the compound containing 

 zinc chemically combined may be supposed to give the rays of zinc 

 more readily than the exploding gases, which merely take up the 

 metal mechanically. But the flame does not, in either case, seem hot 

 enough to develop the ultra-violet rays, though these are very strongly 

 developed in the arc. 



IX. " Preliminary Not'e on the Pressure developed by some 

 New Explosives." By Captain NOBLE, C.B., F.R.S. Re- 

 ceived June 10, 1892. 



For a considerable time I have, with the assistance of Sir F. Abel 

 and Professor Dewar, been engaged in researches upon the new ex- 

 plosives which during the last few years have attracted so much 

 attention, and which apparently are destined to do much in develop- 

 ing the power of modern artillery. 



From the nature of these researches and the considerable scale 

 upon which they have to be conducted, as well as from certain diffi- 

 culties which have manifested themselves, I am not at present in a 

 position to submit to the Royal Society the results of these experi- 

 ments ; but, as one particular portion throws light upon a question of 

 considerable importance, I propose very shortly to give the results at 

 which I have arrived, leaving fuller details for a subsequent communi- 

 cation. 



Artillerists of all nations are pretty well agreed that, save under 

 exceptional circumstances, the maximum working pressure in a gun 

 should not exceed 17 tons per square inch or, say 2500 atmospheres. 

 The reasons for this limitation are weighty, but I need not here dis- 

 cuss them. Now, taking cordite and pebble powder as illustrations, 

 since we can, even in guns not designed to fire the former explosive, 

 obtain with the same maximum pressure, energies higher than those 

 obtained with pebble powder by nearly 50 per cent., it is obvious that 



