Chapter III: NITRO-CELLULOSE, &c (3)

The production of penta-nitro-starch is effected by adding 20 grms. of rice-starch--previously dried at a temperature of 100 deg.C., in order to eliminate all moisture--to a mixture of 100 grms. of nitric acid, specific gravity 1.501, and 300 grms. of sulphuric acid, specific gravity 1.8 (some tetra-nitro-starch is also formed at the same time). After standing in contact with these mixed acids for one hour the starch has undergone a change, and the mass may now be discharged into a large quantity of water, and then washed, first with water, and finally with an aqueous solution of soda. The yield in Dr Muehlhaeusen's experiments was 147.5 per cent.

The substance thus formed is now heated with ether-alcohol, the ether is distilled off, and the penta-nitro-starch appears as a precipitate, whilst the tetra-nitro-starch, which is formed simultaneously, remains in solution in the alcohol. As obtained by this process, it contained 12.76 and 12.98 per cent. nitrogen, whilst the soluble tetra-nitro-starch contained 10.45 per cent.

Hexa-nitro-starch is the product chiefly formed when 40 grms. of dry starch are treated with 400 grms. of nitric acid, specific gravity 1.501, and allowed to stand in contact for twenty-four hours; 200 grms. of this mixture are then poured into 600 c.c. of sulphuric acid of 66 deg. B. The result of this manipulation is a white precipitate, which contains 13.52-13.23 and 13.22 per cent. nitrogen; and consists, therefore, of a mixture of penta- and hexa-nitro-starch.

The experiments undertaken with these substances demonstrated that those prepared by precipitating the nitro-starch with strong sulphuric acid were less stable in character or properties than those which were precipitated by water or weak sulphuric acid. Dr Muehlhaeusen is of opinion that possibly in the former case a sulpho-group may be formed, which in small quantity may occasion this instability.

The following table shows the behaviour of these substances prepared in different ways and under various conditions:--

__________________________________________________________________ | | | | | SAMPLES. | | |____________________________________________| | | | | | | | | | A. | B. | C. | D. | E. | | Ignition-point |175 deg. C. |170 deg. C. |152 deg. C. |121 deg. C. |155 deg. C. | | Stability |Stable |Stable |Unstable|Unstable|Unstable| | Per cent. of N. | 11.02 | 10.54 | 12.87 | 12.59 | 13.52 | | 96 per cent. alcohol| Sol. | Sol. | Insol. | Insol. | Insol. | | Ether | Insol. | Insol. | Insol. | Insol. | Insol. | | Ether-alcohol | Sol. | Sol. | Sol. | Sol. | Sol. | | Acetic Ether | Sol. | Sol. | Sol. | Sol. | Sol. | |_____________________|________|________|________|________|________|

These samples were prepared as follows:--

A. From 1 part nitric acid and 2 parts sulphuric acid (containing 70 per cent. H_{2}O). B. From 1 part nitric acid and water. C. From 1 part nitric and 3 parts H_{2}SO_{4} (con.). D. From 1 part nitric and 3.5 parts con. H_{2}SO_{4}. E. From 1 part nitric and 3 parts con. H_{2}SO_{4}.

Dr Muehlhaeusen is of opinion that these compounds may be turned to practical account in the production of good smokeless powder. He recommends the following proportions and method. Six grms. of nitro-jute and 2 grms. of nitro-starch are mixed together, and moistened with acetic ether. These ingredients are then worked together into a uniform mass, and dried at a temperature ranging between the limits 50 deg. to 60 deg. C. He has himself prepared such a smokeless powder, which proved to contain 11.54 per cent. of nitrogen, and was very stable. Further details of Dr Muehlhaeusen's work upon nitro-starch can be found in _Dingler's Polytechnisches Journal_, paper "Die hoehren Salpetersaeureaether der Staerke," 1892, Band 284, s. 137-143, and a Bibliography up to 1892 in _Arms and Explosives_, December 1892.

M. Berthelot gives the heat of formation of nitro-starch as 812 cals. for 1 grm., and the heat of total combustion as equal to 706.5 cals. for 207 grms., or for 1 grm. 3,413 cals. The heat of decomposition could only be calculated if the products of decomposition were given, but they have not as yet been studied, and the quantity of oxygen contained in the compound is far from being sufficient for its complete combustion. Berthelot and Vieille found the average velocities for nitro-starch powder, density of charge about 1.2, in a tin tube 4 mm. external diameter, to be, in two experiments, 5,222 m. and 5,674 m. In a tin tube 5.5 mm. external diameter, the velocity was 5,815 m., and in lead tube 5,006 m. (density 1.1 to 1.2). The starch powder is hygroscopic, and is insoluble in water and alcohol. When dry it is very explosive, and takes fire at about 350 deg. F. Mr Alfred Nobel has taken out a patent (Eng. Pat. No. 6,560, 88) for the use of nitro-starch. His invention relates to the treatment of nitro- starch and nitro-dextrine, for the purpose of producing an explosive powder, to be used in place of gunpowder. He incorporates these materials with nitro-cellulose, and dissolves the whole in acetone, which is afterwards distilled off. A perfect incorporation of the ingredients is thus brought about.

~Nitro-Jute.~--It is obtained by treating jute with nitric acid. Its properties have been studied by Messrs Cross and Bevan (_Jour. Chem. Soc._, 1889, 199), and by Muehlhaeusen. The latter used for its nitration an acid mixture composed of equal parts of nitric and sulphuric acids, which was allowed to act upon the jute for some time. He found that with long exposure, i.e., from three to four hours in the acids, there was a disintegrating of the fibre-bundles, and the nitration was attended by secondary decomposition and conversion into products soluble in the acid mixture. Cross and Bevan's work upon this subject leads them to conclude that the highest yield of nitrate is represented by an increase of weight of 51 per cent. They give jute the empirical formula C_{12}H_{18}O_{9} (C = 47 per cent. H = 6 per cent., and O = 47 per cent.), and believe its conversion into a nitro compound to take place thus:--

C_{12}H_{18}O + 3HNO_{3} = C_{12}H_{15}O_{6}(NO_{3})_{3} + 3H_{2}O.

This is equivalent to a gain in weight of 44 per cent. for the tri- nitrate, and of 58 per cent. for the tetra-nitrate. The formation of the tetra-nitrate appears to be the limit of nitration of jute-fibre. In other words, if we represent the ligno-cellulose molecule by a C_{12} formula, it will contain four hydroxyl (OH) groups, or two less than cellulose similarly represented. The following are their nitration results:--

Acids used.--I. HNO_{3} sp. gr. 1.43, and H_{2}SO_{4} = 1.84 equal parts.
II. 1 vol. HNO_{3}(1.5), 1 vol. H_{2}SO_{4}(1.84).
III. 1 vol. HNO_{3}(1.5), 75 vols. H_{2}SO_{4}(1.84).

I. = 144.4; II. = 153.3; III. = 154.4 grms.; 100 grms. of fibre being used in all three cases.

Duration of exposure, thirty minutes at 18 deg. C.

The nitrogen was determined in the products, and equalled 10.5 per cent. Theory for C_{12}H_{15}O_{6}(NO_{3})_{3} = 9.5 per cent. and for C_{12}H_{15}O_{6}(NO_{3})_{4} = 11.5 per cent. These nitrates resemble those of cellulose, and are in all essential points nitrates of ligno- cellulose.

Muehlhaeusen obtained a much lower yield, and probably, as pointed out by Cross and Bevan, a secondary decomposition took place, and his products, therefore, probably approximate to the derivatives of cellulose rather than to those of ligno-cellulose, the more oxidisable, non-cellulose, or lignone constituents having been decomposed. In fact, he regards his product as cellulose penta-nitrate (C_{12}H_{16}O_{5}(ONO_{2})_{5}). The _Chemiker Zeitung_, xxi., p. 163, contains a further paper by Muehlhaeusen on the explosive nitro-jute. After purifying the jute-fibre by boiling it with a 1 per cent. solution of sodium carbonate, and washing with water, he treated 1 part of the purified jute with 15 parts of nitro-sulphuric acid, and obtained the following results with different proportions of nitric to sulphuric acids:--

Yield Ignition Nitrogen.
per cent. Point.
Experiment I.-- 1. HNO_{3} 1. H_{2}SO_{4} 129.5 170 deg. C. 11.96%
" II. " 2. " 132.2 167 deg. C. 12.15%
" III. " 3. " 135.8 169 deg. C. 11.91%

An experiment made with fine carded jute and the same mixture of acids as in No. II. gave 145.4 per cent. nitro-jute, which ignited at 192 deg. C., and contained 12 per cent. nitrogen. This explosive is not at present manufactured upon the large scale, and Messrs Cross and Bevan are of opinion that there is no very obvious advantage in the use of lignified textile fibre as raw materials for explosive nitrates, seeing that a large number of raw materials containing cellulose (chiefly as cotton) can be obtained at a cheaper rate, and yield also 150 to 170 per cent. of explosive material when nitrated, and are in many ways superior to the products obtained hitherto from jute.

~Nitro-mannite~ is formed by the action of nitric acid on mannite, a hex-acid alcohol closely related to sugar. It occurs abundantly in manna, which is the partly dried sap of the manna-ash (_Fraxinus ornus_). It is formed in the lactic acid fermentation of sugar, and by the action of nascent hydrogen on glucose and cellulose, or on invert sugar. Its formula is C_{6}H_{8}(OH)_{6} and that of nitro-mannite C_{6}H_{8}(NO_{3})_{6}. Mannite crystallises in needles or rhombic prisms, which are soluble in water and alcohol, and have a sweet taste. Nitro-mannite forms white needle-shaped crystals, insoluble in water, but soluble in ether or alcohol. When rapidly heated, they ignite at about 374 deg. F., and explode at about 590 deg. F. It is more susceptible to friction and percussion than nitro-glycerine, and unless pure it is liable to spontaneous decomposition. It is considered as the nitric ether of the hexatomic alcohol mannite. It is formed by the action of a mixture of nitric and sulphuric acids upon mannite--

C_{6}H_{8}(OH)_{6} + 6HNO_{3} = C_{6}H_{8}(NO_{3})_{6} + 6H_{2}O.

Its products of explosion are as shown in the following equation:--

C_{6}H_{8}(OH)_{6} = 6CO_{2} + 4H_{2}O + 3N_{2} + O_{2}.

Its percentage composition is as follows:--Carbon, 15.9 per cent.; hydrogen, 1.8 per cent.; nitrogen, 18.6 per cent.; and oxygen, 63.7 per cent. Its melting point is 112 to 113 deg. C., and it solidifies at 93 deg.. When carefully prepared and purified by recrystallisation from alcohol, and kept protected from sunlight, it can be kept for several years without alteration.

Nitro-mannite is more dangerous than nitro-glycerine, as it is more sensitive to shock. It is intermediate in its shattering properties between nitro-glycerine and fulminate of mercury. It explodes by the shock of copper on iron or copper, and even of porcelain on porcelain, provided the latter shock be violent. Its heat of formation from its elements is +156.1 calories. It is not manufactured upon the commercial scale.

Besides the nitro compounds already described, there are many others, but they are of little importance, and are none of them made upon the large scale. Among such substances are _nitro-coal_, which is made by the action of nitric acid on coal; _nitro-colle_, a product which results from the action of nitric acid on isinglass or gelatine, soaked in water. It is then treated with the usual acids.

Another method is to place strong glue in cold water until it has absorbed the maximum amount of the latter. The mixture is solidified by the addition of nitric acid, nitrated in the usual way, and well washed. Abel's _Glyoxiline_ is only nitrated gun-cotton impregnated with nitro- glycerine. Nitro-lignine is only nitro-cellulose made from wood instead of cotton; and nitro-straw is also only nitro-cellulose. The explosive known as _Keil's Explosive_ contains nitro-glucose. Nitro-molasses, which is a liquid product, has also been proposed, and nitro-saccharose, the product obtained by the nitration of sugar. It is a white, sandy, explosive substance, soluble in alcohol and ether. When made from cane sugar, it does not crystallise; but if made from milk sugar, it does. It has been used in percussion caps, being stronger and quicker than nitro-glycerine. It is, however, very sensitive and very hygroscopic, and very prone to decomposition. Nitro-tar, made from crude tar-oil, by nitration with nitric acid of a specific gravity of 1.53 to 1.54. Nitro-toluol is used, mixed with nitro-glycerine. This list, however, does not exhaust the various substances that have been nitrated and proposed as explosives. Even such unlikely substances as horse dung have been experimented with. None of them are very much used, and very few of them are made upon the manufacturing scale.