William Richard Eaton Hodgkinson

“ It is afterwards ground into a fine powder and sifted as in the case of the charcoal.
Potassium nitrate is eminently suitable as an oxygen-provider, not being deliquescent. Nitrates are continually being produced in surface soils, &c., by the oxidation of nitrogenous substances. Nitric and nitrous acids are also produced by electric discharges through the atmosphere, and these are found eventually as nitrates in soils, &c. Nitre is soluble in water, and much more so in hot than in cold. Crude nitre, obtained from soils or other sources, is purified by recrystallization. ”

“ Up to a certain pressure, hardness, density, and size of grain of a powder have an effect on the rate of burning and therefore on pressure. Glazing or polishing powder grains, also exerts a slight retarding action on burning and enables the powders to resist atmospheric moisture better. Excess of moisture in gunpowder has a marked effect in reducing the explosiveness. All powders are liable to absorb moisture, the quality and kind of charcoal being the main determinant in this respect; hard burnt black charcoal is least absorbent. ”

“ Guncottons are examined for degree of nitration by the nitrometer, in which apparatus they are decomposed by sulphuric acid in contact with mercury, and all the nitrogen is evolved as nitric oxide, NO, which is measured and the weight of its contained nitrogen calculated. Ordinary guncottons seldom contain more than 13% of nitrogen, and in most cases the amount does not exceed 12.5%. Generally speaking, the lower the nitrogen content of a guncotton, as found by the nitrometer, the higher the percentage of matters soluble in a mixture of ether-alcohol. ”

“ When pure there can only be one kind of saltpetre or sulphur, because they are chemical individuals, but charcoal is not. Its composition, rate of burning, &c., depend not only on the nature of the woody material from which it is made, but quite as much on the temperature and time of heating employed in the making. The woods from which it is made contain carbon, hydrogen and oxygen, and the two latter are never thoroughly expelled in charcoal-making. ”

“ Assuming the above formula to represent guncotton, there is sufficient oxygen for internal combustion without any carbon being left. The gaseous mixture obtained by burning guncotton in a vacuum vessel contains steam, carbon monoxide, carbon dioxide, nitrogen, nitric oxide, and methane. When slowly heated in a vacuum vessel until ignition takes place, some nitrogen dioxide, NO2, is also produced. When kept for some weeks at a temperature of 100° in steam, a considerable number of fatty acids, some bases, and glucose-like substances result. ”

“ Corned or grained powder was adopted in France in 1525, and in 1540 the French utilized an observation that large-grained powder was the best for cannon, and restricted the manufacture to three sizes of grain or corn, possibly of the same composition. Early in the 18th century two or three sizes of grain and powder of one composition appear to have become common. The composition of English powder seems to have settled down to 75 nitre, 15 charcoal, and 10 sulphur, somewhere about the middle of the 18th century. ”

“ In the manufacture glycerin is dropped in a very thin stream into a mixture of 3 parts of nitric (sp. gr. 1.5) and 5 parts of sulphuric acid (sp. gr. 1.84) , the containing vessel being cooled by a water jacket and the acid mixture agitated by a stream of cooled air, the temperature being kept at about 15° C. A considerable excess of acids is necessary for the completion and safety of the reaction, usually about 8 parts of the acid mixture to 1 of glycerin. The higher the strength of the acids the higher the yield of nitroglycerin and the smaller the loss by solution in the waste acids. ”

“ The so-called collodion cottons are nitrated celluloses, but of a lower degree of nitration (as a rule) than guncotton. They are sometimes spoken of as “lower” or “soluble” cottons or nitrates. The solubility in ether-alcohol may be owing to a lower degree of nitration, or to the temperature conditions under which the process of manufacture has been carried on. If guncotton be correctly represented by the formula C6H7O2 (NO3) 3, it should contain a little more than 14% of nitrogen. ”

“ Some of the sulphur is lost, part combining with the metal of the apparatus and part with hydrogen in the charcoal. The military powders of most nations can be represented by the formula 16KNO3 + 21.2C + 6.6S, proportions which are reasonably near to a theoretical mixture, that is one giving most complete combustion, greatest gas volume and temperature. The combustion of powder consists of two processes: (i.) oxidation, during which potassium carbonate and sulphate, carbon dioxide and nitrogen are mainly formed, and (ii.) ”

“ Under different pressures the relative amounts of the combustion products vary considerably. Under very great pressures carbon monoxide, steam and nitrogen are the main products, but nitric oxide never quite disappears.
Dilute mineral acids have little or no action on guncotton. Strong sulphuric acid in contact with it liberates first nitric acid and later oxides of nitrogen, leaving a charred residue or a brown solution according to the quantity of acid. It sometimes fires on contact with strong sulphuric acid, especially when slightly warmed. ”

“ The constitution of guncotton is a difficult matter to investigate, primarily on account of the very insoluble nature of cellulose itself, and also from the fact that comparatively slight variations in the concentration and temperature of the acids used produce considerable differences in the products. The nitrates are also very insoluble substances, all the so-called solvents merely converting them into jelly. ”

“ Reference is made to an explosive mixture as known before his time and employed for “diversion, producing a noise like thunder and flashes like lightning.” In one passage Bacon speaks of saltpetre as a violent explosive, but there is no doubt that he knew it was not a self-explosive substance, but only so when mixed with other substances, as appears from the statement in De secretis operibus artis et naturae, printed at Hamburg in 1618, that “from saltpetre and other ingredients we are able to make a fire that shall burn at any distance we please.” ”

“ The behaviour of small quantities of any explosive is hardly ever indicative of its behaviour in large quantities and especially when under confinement. Hime is of opinion that Bacon blundered upon gunpowder whilst playing with some incendiary composition, such as those mentioned by Marcus Graecus and others, in which he employed his comparatively pure saltpetre instead of crude nitrum. ”

“ When quite dry guncotton is easily detonated by a blow on an anvil or hard surface. If dry and warm it is much more sensitive to percussion or friction, and also becomes electrified by friction under those conditions. ”

“ By rapidly cooling and agitating the nitre solution crystals are obtained of sufficient fineness for the manufacture of powder without special grinding. Nitre contains nearly 48% of oxygen by weight, five-sixths of which is available for combustion purposes. Nearly all the gases of the powder explosion are derived from the nitre. ”

“ The mechanical action of rollers on the powder paste is a double one: not only crushing but mixing by pushing forwards and twisting sideways. The pasty mass is deflected so that it repeatedly comes under first one roller and then the next by scrapers, set at an angle to the bed, which follow each wheel. ”

“ The burning would then start from the comparatively small surfaces of the perforations, which would become larger as the powder burnt away. Experiments bore out this theory perfectly. It was found that small prisms were more convenient to make than large disks, and as the prisms practically fit together into a disk the same result was obtained. This effect of mechanical density on rate of burning is good only up to a certain pressure, above which the gases are driven through the densest form of granular material. ”

“ On its thoroughness depends the removal of small quantities of products other than the nitrates, for instance, some sulphates and products from impurities contained in the original cellulose. Cellulose sulphates are one, and possibly the main, cause of instability in guncotton, and it is highly desirable that they should be completely hydrolysed and removed in the washing process. The nitrated product retains the outward form of the original cellulose. ”

“ However much compressed by mechanical means it is still a porous mass, and when it is confined as in a gun the flame and hot gases from the portion first ignited permeate the remainder, generally causing it actually to detonate, or to burn so rapidly that its action approaches detonation. ”

“ Modern smokeless powders are certainly less noisy than the black powders, mainly because of the absence of metallic salts which although they may be gaseous whilst in the gun are certainly ejected as solids or become solids at the moment of contact with air. ”

“ Less dense powders burn more rapidly from the first and tend to put a great strain on the gun. Fouling is usually less with denser powders; and, as would be expected, such powders bear transport better and give less dust than light powders. ”

“ It is frequently given as 43° to 46° F. (about 6° to 8° C.) , and it is stated to be more sensitive to percussion when frozen (Beilstein) . It crystallizes (in long needles) more easily when gently agitated during the cooling, or when mixed with such substances as kieselguhr. ”