(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 ANALYSIS 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 titrate 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 quantity 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 passed 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-glass, 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 quantity 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 analysed 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 analysis 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.