638 



NATURE 



[February 3, 19 16 



unite with i6 grams of oxygen to form 28 grams of 

 carbon monoxide with the liberation of 29 large 

 Calories, and the same quantity of carbon unites with 

 32 grams of oxygen with the liberation of 97 large 

 Calories. 



Consequently an explosive is considerably more 

 efficient if it contains sufficient oxygen to oxidise the 

 carbon entirely to dioxide, but the effect is reduced 

 to some extent by the relatively high specific heat of 

 carbon dioxide. In some classes of explosives, how- 

 ever, a very high temperature is objectionable ; this is 

 the case with smokeless powders and explosives for 

 use in coal mines. Smokeless powders, therefore, are 

 generally made of such a composition that the greater 

 part of the carbon is oxidised only to monoxide. But 

 there is always some carbon dioxide formed, for it 

 takes up some of the oxygen from the water vapour 

 and liberates hydrogen, or if the total quantity of 

 oxygen be very small there may even be free carbon 

 produced. In the case of safety explosives for coal 

 mines, the temperature of explosion is also sometimes 

 kept low by restricting the proportion of oxygen, but 

 fhis means is not free from objection because carbon 

 monoxide is poisonous. Other methods are therefore 

 adopted in some safety explosives to reduce the tem- 

 perature. 



Oxygen Carriers. — ^The oxygen may either be con- 

 tained in a separate compound, such as saltpetre, 

 which is mixed mechanically with the combustible 

 material, or the two may be combined together in a 

 single compound, as is the case with nitroglycerine, 

 trotyl, and many other modern explosives. The sub- 

 stances rich in oxygen are often referred to as " oxygen 

 carriers " ; those most used are nitrates, chlorates, and 

 perchlorates, in which the oxygen is united to nitrogen 

 and chlorine respectively. Ordinary gunpowder, or 

 "black powder," belongs to the class of explosives 

 that have separate oxygen carriers, in this case salt- 

 netre. The following table shows the properties of the 

 •principal oxygen carriers : — 



Oxyeen 



carrier 



Nitrates. 

 Potassium ... 

 Sodium 

 Calcium 

 Barium 

 Lead 

 Ammonium 



Chlorates. 

 Potassium ... 1226 

 Sodium ... io6'5 

 304-3 



Molecular 

 weight 



lOI'I 



85-0 



164-1 



2615 



33I-I 

 8o-i 



Density 



pose them than the nitrates, and have more available 

 oxygen. As they are now produced at quite low cost 

 by electrolytic methods, it is not surprising to find that 

 they are being used more and more for the manu- 

 facture of explosives. Ammonium nitrate and per- 

 chlorate decompose with the evolution of heat, this 

 being due to the formation of water, but the avail- 

 able oxygen is diminished by the same cause. Ammo- 

 nium nitrate can be detonated by itself, although 

 only with difficulty, and then gives a large volume 

 of gas at a comparatively low temperature. In conse- 

 quence of this low temperature it has been found 

 very useful as a constituent of safety explosives for 

 use in coal mines, but it also forms part of many 

 other high explosives. Ammonium perchlorate suffers 

 under the disadvantage that amongst its products of 

 explosion is the poisonous gas, hydrogen chloride, or 

 hydrochloric acid. 



Potassium permanganate and bichromate have also 

 been used, but they possess no special advantages. Per- 

 manganate explosives are often inconveniently sensitive. 

 Attempts have also been made to use liquid oxygen, 

 which has the advantage of being cheap and contain- 

 ing 100 per cent, of available oxygen, but the diffi- 

 culties of employing a liquid which boils at 200° C. 

 below the ordinary temperature are so great that these 

 attempts were given up. The Germans are, however, 

 making great efforts to develop these explosives for 

 work in mines, so as to set free a corresponding 

 quantity of nitrates for military use. For the same 

 reason the German authorities are encouraging the 

 use of chlorates and perchlorates. 



Combustible Constituents. — In- black powder the 

 combustibles are charcoal and sulphur ; in blasting 

 explosives many sorts of organic matter have been 

 used or proposed, and some inorganic substances, such 

 as potassium ferrocyanide, ammonium oxalate, and 

 antimony sulphide, but those in common use are not 

 very numerous. For explosives containing nitro- 

 glycerin an absorbent material must be used, and of 



Barium 



Perchlorates 

 Potassium , 

 Sodium 

 Barium 

 Ammonium 



138-6 

 122-5 

 336-3 

 .17-5 



2-o8 ... 2KN03 = K.,0 + N,-i-50 



2-26 ... 2NaN63 = Na,0+'N,-f-50 



2-36 ... Ca(N03), = Ca'0 + N2-t-50 



32 ... Ba(N03);=F5aO + N, + 50 



4-58 ... Pb(N03).; = PbO + N; + 50 



1-71 ... NH4N63 = 2H.,0-t-N2 + 



2-00 ... KC103 = KCl + 30 ... 

 2-29 ... NaC103=NaCl + 30 

 3-18 ... Ba(Cl(:>3) = BaCl, + 60 



254 ... KC104=KCl4-40 ... 



— ... NaC104 = NaCl + 40 



— ... Ba(CI04V,= BaCl. + 60 



189 ... 2NH4Cr64 = 2HCl + 3H.,0 + 50 



It will be seen that the proportion of available 

 oxygen is about the same in the chlorates as in the 

 corresponding nitrates, but whereas the chlorates de- 

 compose with the evolution of a small amount of heat, 

 the nitrates require a considerable amount of heat to 

 split them up, except in the case of the ammonium 

 compound. Explosives containing chlorates are conse- 

 quently much more powerful than those containing 

 nitrates, but they are also very sensitive unless special 

 measures are adopted to render them more inert. The 

 perchlorates require considerably less heat to decom- 



NO. 2414, VOL. 96] 



these wood meal is the most usual, but flour and 

 starch are constituents of some nitroglycerin explo- 

 sives, and in a few cases such substances as tan meal 

 and prepared horse-dung are present. Cork charcoal 

 has great absorptive power, but its high cost prevents 

 its use. Ordinary charcoal is a constituent of some 

 explosives, as also is coal-dust. American dynamites 

 often contain resin and sulphur, and these constituents 

 are sometimes met with in other explosives. Oily mate- 

 rials, such as castor oil, vaselin, and paraffin wax, 

 reduce the sensitiveness of an explosive, and one or 



