(Translated from the Russian by Lieutenant John B. Bernadou, U. S. Navy.)
The very favorable results obtained with pyro-collodion and its adaptability to arms of all calibers depend upon its composition and properties, which, for purposes of illustration, may be compared with those of other materials employed as smokeless powders.
As to its chemical composition, pyro-collodion may be designated homogeneous,[*] and herein consists one of its most important qualities. All previous and present forms of powder did not have or do not have this property to the degree here implied. From their very method of preparation, black and brown powders are coarse mechanical mixtures, for which any consideration of homogeneity is out of the question. The same is true for those smokeless powders containing ammonium nitrate, picrates, etc. Nitro-glycerine powders may be regarded as gelatinous solutions of nitro-cellulose in nitro-glycerine, which, from their composition, are, chemically, non-homogeneous; moreover, various solvents (alcohol, ether, acetone, etc.) dissolve certain constituents out of them, leaving others.
The same may be said of present-day types of nitro-cellulose powders; alcohol dissolves out of them the nitro-celluloses of lower nitration; a mixture of ether and alcohol, the collodions, leaving the excess of highly nitrated cellulose undissolved. Pyro- collodion,[†] however, surrenders no part of its substance to alcohol, while it is wholly soluble in a mixture of ether and alcohol. This chemical homogeneity of pyro-collodion, taken in the sense in which it is stated to be employed, plays an important role in its combustion; for there are many reasons for believing that in the case of the combustion of those physically but not chemically homogeneous substances, such as the nitro-glycerine powders (ballistite, cordite, etc.), the nitro-glycerine portion is decomposed first and the nitro-cellulose portion burns subsequently, in a different layer of the powder.[‡] It is to be added that the homogeneity of pyro-collodion possesses a direct bearing upon the uniformity of ballistic results developed by its use.
Besides chemical homogeneity, pyro-cellulose and the powders prepared therefrom possess a second distinguishing quality, viz. that for a given weight of their substance they develop a maximum volume of evolved gases, the latter being measured at a given temperature and pressure. This new conception involves certain intricacies and complexities, and may be discussed to some degree of fulness, in what relates to nature and amount of gases evolved upon the decomposition of powder.
According to the law of Avogadro-Gérard,[§] the chemical equivalents or quantities of matter expressed by simultaneous chemical formulae (e. g., H2O = 18, water; CO = 28, carbonic oxide; CO2 = 44, carbonic acid; N2 = 28, nitrogen) occupy at a given temperature and pressure the same volume as is occupied by two parts by weight of hydrogen H2 = 2 (its molecular equivalent). Consequently, if we possess the full chemical equation of combustion of a substance or mixture of substances, for which the products are gases or vapor, it is easy to calculate the volume occupied by these products at a given temperature and pressure. For example: the combustion of black powder may be expressed typically by the equality,
2KNO3 + S + 3C =K2S + 3CO2 + N2.
Weight, 2.101 +32 + 3.12=110 + 3.44 +28 = 270.
Volume in form of gases, 3.2 +2 =8.
That is, for 270 parts by weight of powder ingredients 8 volumes of gas[**] are formed, or 29.6 volumes for 1000 parts by weight of explosive. Brown powder (cocoa) represents (in its greater progressiveness of combustion and in certain other respects) a partial transformation from black to smokeless powders, and is characterized by the partial carbonization of its charcoal (which contains much hydrogen and approximates to a composition C6H4O), and by the small amount of sulphur entering into its composition. Its mode of combustion may be expressed approximately as
6KNO3 + 2C5H4O = 3K2CO3 + 7CO + 4H2O + 3N2.
6.101 + 2.80 = 3.138 + 7.28 + 4.18 + 3.28 =766.
Volume of gases, 7.2 + 4.2 + 3.2 = 28.
V1000 = 36.5,
or as follows:
4KNO3 + C5H4O + S = K2SO4 + K2CO3 + 4CO + 2H2O + 2N2.
Weight = 516, volume of gases = 16.
V1000 = 31.0.
It is evident, then, that the gas volume corresponding to brown powder is nearly 34,—greater than that for black powder; whence originates the preference generally accorded to brown powder over black.
In a similar manner we have for the complete (typical) combustion of nitro-glycerine,
4C3H5N3O2 = 12CO2 + 10 H2O + 6N2 + O2.
Weight, 4.227 = 12.44 + 10.18 + 6.28 + 32 = 908.
Volume of gases = 12.2 + 10.2 + 6.2 + 2 = 58.
V1000 = 63.9.
If we present in the same manner the decomposition of a type nitro-cellulose of high nitration, such as Abel’s tri-nitro-cellulose, C6H7(NO2)3O5, we obtain
2C6H7N3O11 = 3CO2 + 9CO + 7H2O + 3N2
Weight, 2.297 =3.44 + 9.28 + 7.18 + 3.28 = 594.
Volume of gases = 3.2 + 9.2 + 7.2 + 3.2 = 44.
V1000 = 74.1.
If the typical combustion of this nitro-cellulose be presented by the equality
2C6H7N3O11 = 10CO2 + 7H2 + 3N2.
that is, if we assume that water is not formed, and that the oxygen combines wholly with the carbon, then the V1000 remains unchanged, as the volume of gas formed (22.2 = 44) remains as before. Therefore we need not stop to consider how the oxygen is distributed between the carbon and hydrogen in the products of combustion, as the value of V1000 does not vary.[††]
If, for nitro-cellulose of high nitration we substitute Eder’s penta-nitro-cellulose, C12H15(NO2)5O10, which corresponds to a content of 12.75 per cent. nitrogen, and to the composition of ordinary nitro-cellulose employed for smokeless powders, we obtain a greater evolution of gas, for
2C12H15N5O20 = 23CO + 15H2O + 5 N2
Weight, 2.549 = 44 + 23.28 + 15.18 + 5.28 = 1098.
Volume of gases =2 + 23.2 + 15.2 + 5.2 = 88.
V1000 = 80.1.
The increase in volume of gas hereby realized is due to the fact that the quantity of carbonic acid evolved is diminished, while that of carbonic oxide is increased, which causes an increase of total gas volume, since, for the equality
C + O2 = CO2, V1000 = 45.5
and for the equality
C + O = CO, V1000 = 71.4
If we descend to a lower nitration and consider Eder’s tetra- nitro-cellulose, C12H10(NO2)4O10, we have no longer the case of complete combustion; for 20 equivalents of oxygen are required to convert 12 of carbon and 16 of hydrogen into gaseous products and vapors, while there are but 18 of oxygen available, unless we assume the products of combustion as CO, H2O, and H2.[‡‡] It is known, however, that in the case of combustion of carbohydrates low in oxygen the latter combines with the hydrogen, from its greater affinity for that substance, leaving a part of the carbon deposited in an uncombined state. Consequently, such conditions do not correspond to complete combustion.
The formation of CO2 shows that there is a certain excess of oxygen in penta-nitro-cellulose; whereas typical combustion, corresponding to maximum gas volume, requires all carbon to be converted into carbonic oxide. Such typical combustion is afforded by pyro-collodion, whose composition, as shown, corresponds to the formula C30H38N12O49, as is shown by the equation,
5C6H10O5 + 12HNO3 = C30H38(NO2)12O25 + 12H2O
Cellulose. Nitric acid. Pyro-cellulose. Water
In typical combustion it corresponds to the following equality:
C30H38N12O49 = 30CO + 19H2O + 6N2
Weight, 1350 = 30.28 + 19.18 + 6.28 = 1350.
Volume of gases = 30.2 + 19.2 + 6.2 =110.
V1000 = 81.5.
Before proceeding further, we desire to call attention to the fact that, whereas for brown powder we realize a volume of 34 approx., we have here a volume of 81.5, whence, judging from volumes of evolved gases, pyro-collodion should prove 2½ times more powerful than brown powder. Actual experiments show that the powders stand in about this relation to one another. In units of energy per unit for weight of explosive we have
| Pyro-collodion powder. | Brown powder. | Ratio. |
47 mm. R. F. | about 220 | 81.5 | 2.7:1. |
9-in. gun, | " 223 | 90.7 | 2.5:1. |
12-in. gun, | " 210. | 93 | 2.3:1. |
From this it is evident that our computed value of V1000 is in complete accordance with actual experimental results.
In this manner we may consider it as proven that, for a given temperature and pressure, pyro-collodion develops a greater volume of gases (and vapor) than is developed by black or brown powder (for which V1000 = 30), and even greater than for powders prepared from the more highly nitrated forms of nitro-cellulose and for the nitro-glycerine powders.[§§]
In order to establish the full significance of the above deduction, it remains to show (1) that from the standpoint of practical applicability we can foresee no other material capable of developing as great a value for V1000 as pyro-collodion; (2) that the physico-chemical and ballistic qualities necessary in a smokeless powder are developed by pyro-collodion, not in a less, but in an equal or greater degree than by other materials employed as smokeless powders; (3) that the estimate of ballistic efficiency of a smokeless explosive, through consideration of its volume of evolved gas, without regard to conditions of temperature, leads us into no error, although it would at first appear that temperature would have a direct effect upon the practical qualities of a powder.
I. When smokeless powder was first discovered, so many schemes were afloat for meeting general demands that up to the present time there remain as open questions—which form of smokeless powder is the superior, and whether new and still more efficient forms may not be looked for in the future. In order to reply to these inquiries it will be necessary first to glance over the compositions of materials capable of conversion into smokeless powders under the following assumptions: (1) that they leave no solid residue after combustion, and that their gases exercise no injurious effect upon the metal of guns; (2) that they undergo no change upon keeping for long periods of time, and contain no volatile ingredients; (3) that they may be readily prepared in quantities sufficiently abundant for practical needs.
There are but few elements capable of producing gases that do not act upon metals, and, generally speaking, it is useless to try to find others besides hydrogen and nitrogen, and their compounds with oxygen and carbon, that do not act upon gun chambers at the temperatures of combustion of powder. Therefore, in general terms, the composition of those mixtures or compounds suitable for conversion into powder, may be expressed as
CnH2mN2On.
The energy imparted to the projectile is derived from the conversion of the mass of the powder into gases,[***] the transformation being accompanied with the production of great heat. These fundamental conditions serve to limit the number of materials that are capable of conversion into smokeless powder, the limitations arising not only from the above-named practical requirements, but also from the chemical impossibility of existence of many bodies which, if obtainable, would decompose in the manner requisite for efficient ballistic action. Thus, e. g., there does not exist, nor can we look forward to the existence of such a polymer (in the solid or liquid form) of hydrogen H. that would decompose into hydrogen, H2 with a corresponding production of heat.[†††]
If we may not look for explosives among the simplest chemical combinations of the elements, we may perhaps find them among those compounds of nitrogen and hydrogen which stand in the same relation to ammonia, NH3, as the hydrocarbons to methane, CH4. We should thus have corresponding to ammonia the series NnHn + 2 (ex., diamide N2H4, triamide N3H5, etc.) and the series NnHn, NnHn - 2, etc. As the representative of the latter we have, for n = 3, the nitro-hydric acid of Curtius, N3H, which actually is a very explosive body, and which forms salts, e. g. with ammonium N3(NH4) = N4H4, which is also explosive, decomposing into the gases nitrogen and hydrogen with the evolution of heat, although ammonia itself it not susceptible of explosive decomposition, but absorbs heat in the reaction. If such compounds could be easily prepared, and if they possessed the qualities necessary to an efficient smokeless powder, such as non-volatility, good keeping quality, progressiveness in combustion, etc., they would prove especially suitable for conversion into smokeless powders, as the corresponding values of V1000 would be greater than for other powders. Thus we should have for nitro-hydric acid,
2N3H = H2 + 3N2.
Weight, 2.43 = 2 + 3.28 = 86.
Volume of gases, 2 + 3.2 = 8.
V1000 = 93.0.
For NnHn the volume would be still greater, as V1000 = 133.3. But even if they could be conveniently prepared from readily procurable materials it would be useless to consider such products as available for conversion into smokeless powders, for the reason that they do not decompose through gradual or progressive combustion, as is indispensable in a smokeless powder, but detonate or decompose with extreme suddenness; whence, while they might prove suitable for filling mines or shells, they are unadapted for use in cannon. This property of progressive combustion or decomposition in successive strata is possessed only by those substances containing both combustible ingredients and ingredients capable of effecting progressive combustion, such as carbon and hydrogen, which are consumed by the oxygen that is held in close proximity to them but which is not in direct combination with them.
(To be continued.)
[*] Homogeneity, in its full chemical significance, is not claimed, inasmuch as the composition of cellulose itself remains a matter of doubt. The quality is urged from the technical standpoint, in relation to the properties of other smokeless powders. It is possible that a solvent may be found capable of separating pyro-collodion fractionally; but pyro-collodion insoluble in ether or alcohol, but soluble in a mixture of these substances, is far more homogeneous than other forms of nitro-cellulose or any of the nitro-glycerine powders, inasmuch as the latter are readily capable of fractional subdivision.
[†] Under the assumption that the remainder of the solvent is wholly expelled from the powder.
[‡] The experiments of Messrs. I. M. and P. M. Tcheltsov at the Scientific and Technical Laboratory show that for a given density of loading, the composition of the gases evolved by nitro-glycerine powders varies according to the surface area of the grains (t. e. the thickness of strips or cords), a phenomenon not to be observed in the combustion of pyro- collodion powder. There is only one explanation for this, viz. that the nitro-glycerine, which possesses the higher rate of combustion (Berthelot), is decomposed sooner than the nitro-cellulose dissolved in it. This is the reason why the nitro-glycerine powders destroy the inner surfaces of gun chambers with such rapidity.
[§] The development of this law is given in “Principles of Chemistry,” by D. Mendeléef, 6th ed., 1895, chap. 7
[**] If the weights of the equivalents be expressed in grams we may ascertain the volume of gas evolved in litres, when the pressure P (in millimetres of the mercurial column) and the temperature t (in degrees Celsius) are known. Thus, as two equivalent weights of hydrogen and the equivalent of each gas occupy at a temperature t = o and a pressure P = 760 mm. a volume of 22¼ litres, then for I and P this volume becomes
22¼ (1 + 0.00367t) 760/p
Consequently one volume, expressed in grams, occupies, approximately,
(11.1+0.0407t)/p litres
where p corresponds to the number of atmospheres, each of 760 mm.
at 0°; i. e., p = p/760. Thus, in our example, if t= 2000° and p = 2500 atm., the 8 volumes of gas produced by the combustion of 270 grams of powder occupy an actual volume of
8. (11.1 + 0.407 . 2000 )/2500 = 0.296 litre.
At 0° and a pressure of 1 atmosphere we attain a volume of 88.8 litres for 270 grams. In this manner it is easy to proceed to the value V1000 given in the text, the actual volume of evolved gases per kilogram of powder.
[††] It is another matter if a portion of the oxygen continues in combination with the nitrogen, of if the oxygen proves insufficient to convert all the carbon and hydrogen into gases; that is, if hydrocarbons are formed; but this becomes a case of incomplete combustion. Such conditions have a certain bearing upon the combustion of smokeless powders, especially when the solvent is not completely expelled; but, on the one hand, the quantity of hydrocarbons formed is relatively small, and on the other, they are formed (as also compounds of carbon and nitrogen, as cyanogen), in relatively small quantities, for all powders, even when the latter contain an excess of oxygen. In considering type forms of combustion there is no need of investigating secondary conditions of this class, especially as by so doing we are diverted from the direct study of the general problem.
[‡‡] In the latter case (without formation of carbon) the decomposition would be:
C12H16N4O18 = 12CO + 6H2O + + 2H2 + 6N2
Weight, 504 = 12.28 + 6.18 + 2.2 + 2.28 = 504
Volume of gases = 12.2 + 6.2 + 2.2 = 44.
V1000 = 87.5.
But typical combustion, according to such an equation, is practically impossible; carbon and hydrocarbons are formed, and the combustion that actually does occur is intermediate in character to that expressed by the above and by the two following equalities—
2C12H16N4O18 = C4 + 20CO + 12H2O + 4N2.
2C12H16N4O18 = 22CO + 14H2O +C2H4 + 4N2.
For the first, V1000 = 79.4; for the second, 81.4; the mean of the two latter is 80.4; of all three, 82.4. This quantity is close to that afforded by penta-nitro-cellulose and pyro-collodion. In this manner may be explained the phenomenon that upon the combustion of nitro-cellulose containing a little less than 12.5 per cent, nitrogen or of pyro-collodion containing a certain amount of unevaporated solvent (which is equivalent to a lowering of nitration), results are obtained that approximate to those produced by pyro-collodion powder, although velocities and pressures are somewhat lowered. The existence of this phenomenon depends upon the homogeneity of the powder; whence it follows that it is better to have a content of a little less than 12.5 per cent, with a homogeneous powder than a content of above 12.5 per cent, nitrogen with the powder non- homogeneous, and that the best results are developed by homogeneous pyro-collodion of nitration N = 12.4 per cent.
[§§] The rapid, simple and novel method of comparing the force of explosives herein employed was first suggested and used by me in 1892. It was developed through comparison of the composition of smokeless powders and of their products of combustion and of the results of experimental firings made at the Laboratory. Although I see clearly, that not only the volumes of products of combustion, but also their temperatures, must be taken into account in a complete analysis of phenomena attending the decomposition of smokeless powders, nevertheless I purposely give preference in these investigations to phenomena relating to volumes of gases evolved, not only on account of the simplicity of the latter and their direct accordance with ballistic results, but for the reason that with present methods for estimating temperatures developed by explosives (and these methods are unreliable) it becomes necessary to make numerous arbitrary assumptions (especially in relation to specific heats of gases and vapors at high temperatures); while for volume calculations we have definiteness of composition as a starting point; and if there be any assumption to be made, it relates to the distribution of the oxygen between the carbon and hydrogen, which, from the chemical standpoint, it is not so material,—and as far as it relates to volume it is of little significance. In all cases, however, I present but the elementary comparisons of performances of powders, as the fuller treatment of the subject does not constitute the object of my investigation.
[***] And is not derived from an external source of energy, such as the tension of a spring or the physical compression of gases, as in the Giffard gun.
[†††] If such a substance existed, then its decomposition, according to the equation H2n = nH2, would afford a weight 2n for a volume 2n; that is, V1000 would be equal to 1000, the greatest possible value. For nitrogen under similar conditions we would have V1000 = 71.4, or less than for pyro-collodion. But the existence of such a polymer is highly improbable. If argon (vid. Mendeléef, Principles of Chemistry, 6th ed. 1895, p. 749) were the polymer of nitrogen, N3, its conversion into nitrogen could only be accomplished through the absorption of heat; i. e. it would find no place in the category of “explosive” bodies (to which ozone possesses a relation).