Nitro-Explosives: A Practical Treatise Part 18

~Acetone~ (CH_{3}CO.CH_{3}), or dimethyl ketone, is formed when iso-propyl alcohol is oxidised with pota.s.sium bichromate and sulphuric. It is also produced in considerable quant.i.ties during the dry distillation of wood, and many other organic compounds. Crude wood spirit, which has been freed from acetic acid, consists in the main of a mixture of acetone and methyl- alcohol. The two substances may be roughly separated by the addition of calcium chloride, which combines with the methyl-alcohol. On subsequent distillation crude acetone pa.s.ses over, and may be purified by conversion into the bisulphite compound.

Acetone is usually prepared, however, by the dry distillation of crude calcium or barium acetate.

(CH_{3}.COO)_{2}Ca = CH_{3}.CO.CH_{3} + CaCO_{3}.

The distillate is fractionated, and the portion, boiling between 50 and 60 C., mixed with strong solution of sodium bisulphite. The crystalline cake of acetone sodium bisulphite, which separates on standing, is well pressed, to free it from impurities, decomposed by distillation with dilute sodium carbonate, and the aqueous distillate of pure acetone dehydrated over calcium chloride. Acetone is a colourless, mobile liquid of sp. gr. .792 at 20 C., it boils at 56.5 C., has a peculiar, pleasant, ethereal odour, and is mixible with water, alcohol, and ether in all proportions.

The acetone used in the manufacture of cordite should conform to the following specification:--

SPECIFICATION FOR ACETONE.

1. The acetone to be not more than 0.802 specific gravity at 60 F. When mixed with distilled water it must show no turbidity, and must leave no residue on evaporation at 212 F. On distillation, four-fifths by volume of the quant.i.ty taken must distil over at a temperature not exceeding 138 F. The residual matter left after this distillation must not contain, besides acetone, any ingredient that is not a bye-product incidental to the manufacture of acetone.

2. One c.c. of 0.10 per cent. solution in distilled water of pure permanganate of potash, added to 100 c.c. of the acetone, must retain its distinctive colour for not less than 30 minutes. This test should be made at a temperature of 60 F.

3. The acetone tested by the following method must not show more than 0.005 per cent. of acid, calculated to acetic acid:--

To 50 c.c. of the sample diluted with 50 c.c. of distilled water, with 2 c.c. of phenol-phthalein solution (1 gramme to 1,000 c.c. of 50 per cent.

alcohol) added as an indicator, add from a burette N/100 sodium hydrate solution (1 c.c. 0.0006 gramme acetic acid), and calculate to acetic acid in the usual manner.

The water used for the dilution of the acetone must be carefully tested for acidity, and the pipettes used for measuring should not be blown out, as it would be possible thus to neutralise nearly 2 c.c. of the soda solution.

The presence of water in a sample of acetone may be detected by Schweitzer and Lungwitz's method (_Chem. Zeit._, 1895, xix., p. 1384), which consists in shaking together equal volumes of acetone and petroleum ether (boiling point, 40 to 60 C.), when if present a separation of the liquid in layers will take place.

~Estimation of Acetone.~--Kebler (_Jour. Amer. Chem. Soc._, 1897, 19, 316- 320) has improved Squibb's modification of Robineau and Rollins' method.

The following solutions are required:--

(1.) A 6 per cent. solution of hydrochloric acid.

(2.) A decinormal solution of sodium thiosulphate.

(3.) Alkaline pota.s.sium iodide solution prepared by dissolving 250 grms.

of pota.s.sium iodide in water, made up to a litre; dissolving 257 grms. of sodium hydroxide (by alcohol) in water, likewise made up to a litre. After allowing the latter to stand, 800 c.c. of the clear solution are added to the litre of KI.

(4.) Sodium hypochlorite solution: 100 grms. of bleaching powder (35 per cent.) are mixed with 400 c.c. of water: to this is added a hot solution of 120 grms. of crystallised sodium carbonate in 400 c.c. of water. After cooling, the clear liquid is decanted, the remainder filtered, and the filtrate made up to a litre; to each litre is added 25 c.c. of sodium hydroxide solution (sp. gr. 1.29).

(5.) An aqueous solution of the acetone, containing 1 or 2 per cent. of acetone.

(6.) Bicarbonated starch solution prepared by treating 0.125 grm. of starch with 5 c.c. of cold water, then adding 20 c.c. of boiling water, boiling a few minutes, cooling, and adding 2 grms. of sodium bicarbonate.

To 20 c.c. of the pota.s.sium iodide solution are added 10 c.c. of the diluted aqueous acetone, an excess of the sodium hypochlorite solution is then run in from a burette and well shaken for a minute. The mixture is then acidified with the hydrochloric acid solution, and while agitated, an excess of sodium thiosulphate solution is added, the mixture being afterwards allowed to stand a few minutes. The starch indicator is then added, and the excess of thiosulphate re-t.i.trated. The relation of the sodium hypochlorite solution to the sodium thiosulphate being known, the percentage of acetone can be readily calculated.[A]

[Footnote A: See "The Testing of Acetone," Conroy, _Jour. Soc. Chem.

Ind._, 31st March 1900, vol. xix.]

Dr S.J.M. Auld has recently (_Jour. Chem. Soc._, Feb. 15, 1906, vol. xxv.) worked out a volumetric method for the estimation of acetone, depending on the formation of brom.o.f.orm, and its subsequent hydrolysis with alcoholic potash. The hydrolysis is probably expressed thus--

3CHBr_{3} + 9KOH + C_{2}H_{5}OH = 3CO + C_{2}H_{4} + 9KBr + 7H_{2}O

as it has been shown by Hermann and Long that exactly 3 volumes of carbon monoxide to 1 of ethylene are evolved. The residual pota.s.sium bromide is estimated by means of standard silver nitrate solution. Brom.o.f.orm is specially suitable for this purpose for several reasons. It is very readily formed by the action of bromine and potash on acetone, and although very volatile in steam, it is not liable to loss due to its own evaporation. Further, its high molecular weight and large percentage of bromine conduce to accurate results, 58 grms. of acetone being responsible for the formation of 357 grms. of KBr. The method of carrying out the a.n.a.lysis is as follows:--

A known quant.i.ty of the solution to be tested, containing acetone to the extent of 0.1 to 0.2 grm., is pipetted into a 500 c.c. round-bottom flask, diluted with a little water, and mixed with 20 to 30 c.c. of a 10 per cent. solution of caustic potash. The flask is connected with a long reflex condenser, and is also fitted with a dropping funnel containing a solution of bromine in pota.s.sium bromide (200 grms. of Br and 250 grms. of KBr to 1 litre of water). The bromine solution is allowed to flow into the mixture until it has acquired a faint yellow tinge, the flask and its contents being then heated on the water bath at about 70 C. for half-an- hour. Bromine solution is added drop by drop until the slight coloration is permanent, excess of bromine being got rid of by boiling for a minute or two with a little more caustic potash. The mixture is then distilled until the distillate is free from brom.o.f.orm, halogen being tested for in the usual manner. Water is added to the contents of the flask if necessary. It may be here observed that no acetone can be detected in the distillate by means of the mercuric oxide test, and free bromine is also absent. The condenser having been washed out with a little alcohol, in order to remove any traces of brom.o.f.orm which may have collected, the distillate and washings are mixed with 50 c.c. of alcohol and sufficient solid caustic potash to make an approximately 10 per cent. solution. The mixture is then heated on the water bath under a reflux condenser until the brom.o.f.orm is completely decomposed. This generally occupies about three-quarters of an hour. The liquid is allowed to cool, evaporated to smaller bulk if necessary, and exactly neutralised with dilute nitric acid. It is then diluted with water to 500 c.c., and an aliquot part t.i.trated with N/10 silver nitrate solution, using pota.s.sium chromate as indicator; 240 parts of bromine correspond to 58 parts of acetone. The complete a.n.a.lysis can be performed in one and a half to two hours. It is imperative that the bromine used should be pure, as crude bromine frequently contains brom.o.f.orm. The method is suitable for the estimation of acetone in wood-spirit, the spirit being diluted to 10 times its volume, and 5 c.c. of this solution employed for the determination. For example--

(1.) Three c.c. of a solution containing 9.61 per cent. acetone gave 1.7850 grm. KBr. Acetone found = 9.66 per cent.

(2.) Ten c.c. of a solution containing 0.96 per cent. acetone gave 0.5847 grm. KBr. Acetone found = 0.95 per cent.

~Nitro-Cotton.~--The first thing upon opening a case of wet cotton, or in receiving a sample from the "poacher," that requires to be determined is the percentage of water that it contains. It is best done by weighing out about 1,000 grms. upon a paper tray, which has been previously dried in the oven at 100 C. for some time, and become constant in weight. The trayful of cotton is then placed in a water oven, kept at 100 C., and dried as long as it loses water. The loss gives the percentage of water.

It varies from 20 to 30 per cent. as a rule in "wet" cotton.

OUTLINE SCHEME FOR THE a.n.a.lYSIS OF NITRO-EXPLOSIVES _______________________________________________________________________ | | | Exhaust dried substance with Anhydrous Ether in Soxhlet's Fat | | Extraction Apparatus. | |_______________________________________________________________________| | | | _Solution_--Divide into two parts ~A.~ and ~B.~ | |_______________________________________________________________________| | | | ~A.~ | | | | Allow ether to evaporate spontaneously. Dry residue in vacuo over | | H_{2}SO_{4} and weigh. Equals nitro-glycerine, resin, camphor, and | | paraffin. | | | | The nitro-glycerine in this residue may be decomposed by heating | | with a solution of alcoholic potash. Water may then be added, and the | | alcohol evaporated off on the water bath. From this solution the | | resin may be precipitated by HCl, filtered off, dried, and weighed. | | Solution containing the paraffin is treated with AmS solution and | | heated. On cooling the paraffin separates, and may be separated. | | Residue may be shaken with CS_{2} to remove camphor. | |_______________________________________________________________________| | | | ~B.~ | | | | Add phenol-phthalein and t.i.trate with alcoholic potash, 1 c.c. normal | | KHO = .330 grm. _resin_, and add considerably more KHO. Evaporate, | | dissolve residue in water, shake with ether, and separate. | |_______________________________________________________________________| | | | _Ethereal Solution_ evaporated leaves paraffin. | |_______________________________________________________________________| | | | _Aqueous Solution_-- | | Add bromide, acidify with HCl, separate any resin and precipitate, | | filtrate with BaCl_{2} BaSO_{4} x .1373 = Sulphur. | |_______________________________________________________________________| | | | _Residue_-- | | Dry, weigh, and exhaust with water preferably in Soxhlet. | |_______________________________________________________________________| | | | | _Solution_-- | _Residue_-- | | Contains metallic | Dry, weigh, and agitate an aliquot part with | | nitrates, chlorates, | with H_{2}SO_{4} and Hg in nitrometer. If | | soluble carbonates, | nitro-cellulose is present, treat remainder of | | the sum of which | residue with ether-alcohol. | | (except AmCO_{3}) |________________________________________________| | can be determined by | | | evaporating down at | _Solution_-- | | 100 C. to dryness | Evaporate and weigh. Residue consists of | | and weighing. | soluble nitro-cellulose. | | Nitrates can be |________________________________________________| | determined by | | | | _Residue_-- | | | Dry and weigh and determine hexa-nitro- | | | cellulose in nitrometer, if present. Exhaust | | | remainder with acetic ether. | | |________________________________________________| | | | | | | _Solution_-- | _Residue_-- | | | Hexa-nitro-cellulose | Dry and weigh, ignite | | | (Gun cotton). | and reweigh. Loss = | | | | _Cellulose_. | | | |_________________________| | | | | | | | Residue consists of | | | | sawdust, charcoal, | | | | coal, chalk, guhr, | | | | or mineral matter, &c. | |______________________|______________________|_________________________|

NOTE.--Camphor is found by difference. Sulphur is only partially soluble in ether. It is better, therefore, to extract some of the original substance with water, and treat residue with alcoholic KHO. Add bromide, acidify, and precipitate as BaSO.

~The Solubility Test.~--The object of this test is to ascertain, in the case of gun-cotton, the percentage of soluble (penta and lower nitrates) cotton that it contains, or in the case of soluble cotton, the quant.i.ty of gun-cotton. The method of procedure is as follows:--Five grms. of the sample which has been previously dried at 100 C., and afterwards exposed to the air for two hours, is transferred to a conical flask, and 250 c.c.

ether-alcohol added (2 ether to 1 alcohol). The flask is then corked and allowed to digest, with repeated shaking, for two or three hours. The whole is then transferred to a linen filter, and when the solution has pa.s.sed through the filter, is washed with a little ether, and pressed in a hand-screw press between folds of filter paper. The sample is then returned to the flask, and the previous treatment repeated, but it will be sufficient for it to digest for one hour the second time. The filter is then again pressed first gently by hand, then in the press, and afterwards opened up and the ether allowed to evaporate. The gun-cotton is then removed from the filter and transferred to a watch-gla.s.s, and dried in the water oven at 100 C. When dry it is exposed to the air for two hours and weighed. It equals the amount of gun-cotton and unconverted cotton in the 5 grms. The unconverted cotton must be determined in a separate 5 grms.

and deducted.

The method of determining the soluble cotton now used in the Government laboratories is as follows:--Fifty grains of the nitro-cotton are dissolved in 150 c.c. of ether-alcohol, and allowed to stand, with frequent shakings, in a 200 c.c. stoppered measure for six hours; 75 c.c.

of the clear solution are then drawn off by the aid of a pipette and evaporated in a dish on the water bath, and finally in the water oven at 120 F. (49 C.), until constant in weight. The weight found equals the quant.i.ty of soluble cotton in the 75 c.c., which, multiplied by 4, equals the percentage, thus: Suppose that 2.30 grains was the weight found, then

(2.3 x 150)/75 = 4.6 in 50 = 9.20 per cent.

A method for the determination of soluble nitro-cellulose in gun-cotton and smokeless powder has been published by K.B. Quinan (_Jour. Amer. Chem.

Soc._, 23 [4], 258). In this method about 1 grm. of the finely divided dry sample to be a.n.a.lysed is placed in an aluminium cup 1.9 inch in diameter and 4-1/8 inch deep. It is then covered and well stirred with 50 c.c. of alcohol, 100 c.c. of ether are then added, and the mixture is stirred for several minutes. After removing the stirrer, the cup is lightly covered with an aluminium lid, and is then placed in the steel cup of a centrifugal machine, which is gradually got up to a speed of 2,000 revolutions per minute, the total centrifugal force at the position occupied by the cups (which become horizontal when in rapid rotation) is about 450 lbs. They are rotated at the full speed for ten to twelve minutes, and the machine is then gradually stopped. By this time the whole of the insoluble matter will be at the bottom of the cup, and the supernatant solution will be clear. It is drawn off to within a quarter of an inch of the bottom (without disturbing the sediment), with the aid of a pipette.

Care must be taken that the solution thus withdrawn is perfectly clear.

About 10 to 15 c.c. of colloid solution and a film of insoluble matter remain at the bottom of the cup; these are stirred up well, the stirrer is rinsed with ether-alcohol, about 50 c.c. of fresh ether-alcohol are added; the mixture is again treated in the centrifugal apparatus for about eight minutes; the whole washing process is then repeated until all soluble matter has been removed. This may require about seven or eight (or for samples with much insoluble matter ten or twelve or more) washings, but as the extraction proceeds, the period of rotation may be somewhat reduced.

After extraction is completed, the insoluble matter is transferred to a Gooch crucible with the usual asbestos pad, dried at 100 C., and weighed.

The residue may, if wished, be dried and weighed in the aluminium cup, but then it cannot be ignited. The whole time for an a.n.a.lysis exclusive of that required for drying, is from one to two hours--average time, 1-1/4 hour. The results are satisfactory both as to accuracy and rapidity.

Acetone-soluble nitro-cellulose may be determined by the same method.

~The Unconverted or Non-nitrated Cotton.~--However well the cotton has been nitrated, it is almost certain to contain a small quant.i.ty of non- nitrated or unconverted cotton. This can be determined thus:--Five grms.

of the sample are boiled with a saturated solution of sodium sulphide, and then allowed to stand for forty-eight hours, and afterwards filtered or decanted, and again boiled with fresh solutions of sulphide, and again filtered, washed first with dilute HCl and then with water, dried, and weighed. The residue is the cellulose that was not nitrated, plus ash, &c.

It should be ignited, and the weight of the ash deducted from the previous weight.

Acetone, and acetic-ether (ethyl-acetate) may also be used as solvents for the nitro-cellulose. Another process is to boil the gun-cotton, &c., in a solution of sodium stannate made by adding caustic soda to a solution of stannous chloride, until the precipitate first formed is just re-dissolved. This solution dissolves the cellulose nitrates, but does not affect the cellulose. Dr Lunge found the following process more satisfactory in the case of the more highly nitrated products:--The reagent is an alcoholic solution of sodium-ethylate prepared by dissolving 2 to 3 grms. of sodium in 100 c.c. of 95 per cent. alcohol, and mixing the filtered solution with 100 c.c. of acetone. It has no effect upon cellulose, but decomposes nitro-cellulose with the formation of a reddish brown compound, which is soluble in water. In the determination, 5 grms.

of gun-cotton are heated to 40 or 50 C. on the water bath with 150 c.c.

of the reagent, the liquid being shaken at intervals for twenty to thirty minutes; or the mixture may be allowed to stand for a few hours at the ordinary temperature. The brown-red solution is decanted from the undissolved residue, and the latter washed with alcohol and with water, by decantation, and then on the filter with hot water, to which a little hydrochloric acid is added for the final washings. For ordinary work this cellulose is dried immediately and weighed, but in exact determinations it is washed with alcohol, again treated with 50 c.c. of the reagent, and separated and washed as before. The cellulose thus obtained, gives no trace of gas in the nitrometer, and duplicate determinations agree within 0.1 to 0.2 per cent. when the weight of unchanged cellulose amounts to about 0.2 grm. Gun-cotton, which is completely soluble in acetone, contains only traces of cellulose, and when as much as 0.85 per cent. is present it does not dissolve entirely. This method is not applicable to the determination of cellulose in lower nitrated products, and Dr Lunge attributes this to the fact that these being prepared with less concentrated acid invariably contain oxy-cellulose.

~Alkalinity.~--Five grms. of the air-dried and very finely divided sample are taken from the centre of the slabs or discs, and digested with about 20 c.c. of N/2 hydrochloric acid, and diluted with water to about 250 c.c., and shaken for about fifteen minutes. The liquid is then decanted, and washed with water until the washings no longer give an acid reaction.

The solution, together with the washings, are t.i.trated with N/4 sodium carbonate, using litmus as indicator.

~Ash and Inorganic Matter.~--This is best determined by mixing 2 or 3 grms. of the nitro-cotton in a platinum crucible with shavings of paraffin, heating sufficiently to melt the paraffin, and then allowing the contents of the crucible to catch fire and burn away quietly. The temperature is then raised, and the carbonaceous residue incinerated, cooled, weighed, &c., and the percentage of ash calculated. Schjerning proceeds in the following way:--He takes 5 grms. of the nitro-cotton in a large platinum crucible, he then moistens it with a mixture of alcohol and ether, in which paraffin has been dissolved to saturation, and filtered and mixed with one-fourth of its volume of water. Some fragments of solid paraffin are then added, and the ether set on fire. Whilst this is in progress the crucible is kept in an oblique position, and is rotated so that the gun-cotton may absorb the paraffin uniformly. The partially charred residue is now rubbed down with a rounded gla.s.s rod, and the crucible is covered and heated for from fifteen to twenty minutes over the blow-pipe, the lid being occasionally removed. The residue is soon converted into ash, which is weighed, and then washed out into a porcelain basin and treated with hydrochloric acid heated to 90 C. The oxide of iron, alumina, lime, and magnesia are thus dissolved, and the silica remains as insoluble residue. The rest of the a.n.a.lysis is conducted according to the well-known methods of separation. The percentage of ash as a whole is generally all that is required.

~Examination of Nitrated Celluloses with Polarised Light.~--Dr G. Lunge (_Jour. Amer. Chem. Soc._, 1901, 23 [8], 527) has formed the following conclusions:--The most highly nitrated products appear blue in polarised light, but those containing between 13.9 and 13.0 per cent. of nitrogen cannot be distinguished from each other by polarisation. As the percentage of nitrogen rises, the blue colour becomes less intense, and here and there grey fibres can be observed, though not in proportion to the increase in the nitrogen. Below 12.4 per cent. of nitrogen, the fibres show a grey l.u.s.tre, which usually appears yellow when the top light is cut off. Below 10 per cent. of nitrogen, the structure is invariably partially destroyed and no certain observations possible. It is only possible to distinguish with certainty, firstly any unchanged cellulose by its flashing up in variegated (rainbow) colours; and secondly, highly nitrated products (from 12.75 per cent. N upwards), by their flashing up less strongly in blue colours. The purple transition stage in the fibres containing over 11.28 per cent. of N (Chardonnet) was not observed by Dr Lunge.

~Determination of Nitrogen by Lunge Nitrometer.~--The determination of the percentage of nitrogen in a sample of gun-cotton or collodion is perhaps of more value, and affords a better idea of its purity and composition, than any of the foregoing methods of examination, and taken in conjunction with the solubility test, it will generally give the a.n.a.lyst a very fair idea of the composition of his sample. If we regard gun-cotton as the hexa-nitro-cellulose, the theoretical amount of nitrogen required for the formula is 14.14 per cent., and in the same way for collodion-cotton, which consists of the lower nitrates, chiefly, however, of the penta- nitrate, the theoretical nitrogen is 12.75 per cent., so that if in a sample of nitro-cotton the nitrogen falls much lower than 14 per cent., it probably contains considerable quant.i.ties of the lower nitrates, and perhaps some non-nitrated cellulose as well (C_{6}H_{10}O_{5})_{x}, which of course would also lower the percentage of nitrogen.