POTASSIUM, RUBIDIUM, CAESIUM, AND LITHIUM 657 



atures. Its application in gunpowder is based on this property ; gun- 

 powder consists of a mechanical mixture of finely-ground sulphur, nitre, 

 and charcoal. The relative proportion of these substances varies accord- 

 ing to the destination of the powder and to the kind of charcoal employed 

 (a friable, incompletely-burnt charcoal, containing therefore hydrogen 

 and oxygen, is employed). Gases are formed in its combustion, chiefly 

 nitrogen and carbonic anhydride, which create a considerable pressure 

 if their escape be in any way impeded. This action of gunpowder 

 maybe expressed by'the equation : 2KN0 3 + 30 + S = K 2 S + 3C0 2 4- N 2 . 

 It is found by this equation that gunpowder should contain thirty- 

 six parts of charcoal (13'3 p.c.), and thirty-two parts (11-9 p.c.) of sul- 

 phur, to 202 parts (74*8 p.c.) of nitre, which is very near to its actual 

 composition. 16 



16 In China, where the manufacture of gunpowder has long been carried on, 75'7 parts 

 of nitre, 14'4 of charcoal, and 9'9 of sulphur are used. Ordinary powder for sporting 

 purposes contains 80 parts of nitre, 12 of charcoal, and 8 of sulphur, whilst the gunpowder 

 used in heavy ordnance contains 75 of nitre, 15 of charcoal, and 10 of sulphur Gun- 

 powder explodes when heated to 800, when struck, or by contact with a spark. A 

 compact or finely-divided mass of gunpowder burns slowly and has but little disruptive 

 action, because it burns gradually. To act properly the gunpowder must have a definite 

 rate of combustion, so that the pressure should increase during the passage of the 

 projectile along the barrel of the fire-arm. This is done by making the powder in large 

 granules or in the shape of six-sided prisms with holes through them (prismatic 

 powder). 



The products of combustion are of two kinds (1) gases which produce the pressure 

 and are the cause of the dynamical action of gunpowder, and (2) a solid residue, 

 usually of a black colour owing to its containing unburnt particles of charcoal. Besides 

 charcoal, the residue generally contains potassium sulphide, K 2 S, and a whole series of 

 other salts for instance, carbonate and sulphate. It is apparent from this that the 

 combustion of gunpowder is not so simple as it appears to be from the above formula, and 

 hence the weight of the residue is also greater than indicated by that formula. According 

 to the formula, 270 parts of gunpowder give 110 parts of residue that is, 100 parts of 

 |>owder give 87'4 parts of residue, K a S, whilst in reality the weight of the residue varies 

 from 40 p.c. to 70 p.c. (generally 52 p.c.). This difference depends on the fact that so 

 much oxygen (of the nitre) remains in the residue, and it is evident that if the residue 

 varies the composition of the gases evolved by the powder will vary also, and therefore 

 'the entire process will be different in different cases. The difference in the composition 

 of the gases and residue depends, as the researches of Gay-Lussac, Shishkoff and Bun* 

 sen, Nobel and Abel, Federoff, Debus, &c., show, on the conditions under which the 

 combustion of the powder proceeds. When gunpowder burns in an open space, the 

 gaseous products which are formed do not remain in contact with the residue, and then 

 a considerable portion of the charcoal entering into the composition of the powder 

 remains unburnt, because the -charcoal burns after the sulphur at the expense of the 

 oxygen of the nitre. In this extreme case the commencement of the combustion of the 

 gunpowder may be expressed by the equation, 2KNO 3 +8C + S = 2C + K2SO4 + CO 3 + N 3 . 

 The residue in a blank cartridge often consists of a mixture of C, KgSO* K 3 CO 5 , and 

 KjjSjjOs- If the combustion of the gunpowder be impeded if it take place in a cartridge 

 in the barrel of a gun the quantity of potassium sulphate will first be diminished, then 

 the amount of sulphite, whilst the amount of carbonic anhydride in the gases and the 

 amount of potassium sulphide in the residue will increase. The quantity of charcoal 

 entering into the action will then be also increased, and hence the amount in the residue 



