Of the hundreds of different mixtures and compounds discovered to have an explosive nature, perhaps the best known are, gun-powder, gun-cotton, nitro-glycerine, dynamite, mixtures of potassium chlorate, picrate compounds, fulminates of mercury, Silver, copper, etc., and smokeless powder. However those having no bearing on the development of smokeless powder will not be considered.
Gun-powder is the oldest known explosive, and was first used in warfare as early as the year 1350. It is composed of potassium-nitrate, carbon and sulphur, in proportions of 75%, 13%, and 12% respectively, and these proportions have varied but slightly in its entire history.
Gun-powder is purely a mechanical mixture, the various components being finely pulverized, mixed thoroughly, and the fine dust sifted off. Although affected but little by frost or cold, it is susceptible to fire, and moisture renders it useless. Continued experiments following its discovery showed that the violence of its explosion and the time of its burning could be regulated by caking the powder into grains and pellets, which resulted in its continued use for guns of all descriptions.
The disadvantages of the standard type of gun-powder are very apparent. The bore deposit is considerable, rendering a frequent cleaning of the gun necessary. The smoke arising from the discharge of even a small quantity is excessive, and obscures the vision of the gun's crew for a considerable length of time. When used in small arms by skirmishers or sportsmen, it makes the position of the marksman at once evident. Also the limit of velocity for the different calibred guns was soon reached, and no forward steps were being made. It was not, however, until the discovery of gun-cotton and nitro-glycerine, that the possibility of obtaining a smokeless powder was considered.
Smokeless explosives, of which gun-cotton and nitro-glycerine are the most important, were first discovered in 1832, by Braconnot, who found that starch dissolved in nitric acid and then washed out with water became highly explosive. Shortly after, Pelouse obtained the same results by using cotton fabrics instead of starch. It was not until 1846, however, that Schonbein succeeded in obtaining a true gun-cotton, from using a mixed bath of nitric and sulphuric acids. This fibrous cotton was seized upon eagerly as a smokeless explosive, and rammed into cases and used with such disastrous results, that it was soon given up. An Austrian, Von Lenk, persisted in trying to overcome the erratic and violent nature of the explosive by regulating the rate of burning, which he did to some extent by braiding together wisps of uniformly dense fibre.
In 1863, he organized the first smokeless explosive battery, consisting of six 12-pdr. guns, and used the explosive with success for a year. Then two large magazines blew up, from unknown causes, and it was abandoned. The English government had watched these experiments carefully, and they were taken up in 1863 by Sir Frederick Abel. In 1865 he published his process of manufacturing gun-cotton, which marked a new era in the history of this explosive. Although improvements have been made in the machinery, the process practically remains the same to-day, and will be considered later.
Nitro-glycerine was discovered in 1847, by Ascagne Sobrero, just one year after the discovery of gun-cotton, but it was not applied as an explosive until 1864. Nitro-glycerine was prepared by the action of a concentrated mixture of nitric and sulphuric acids on glycerine. The result was an oily liquid, colorless, odorless, with a sweet taste, poisonous, specific gravity of 1.6, and highly explosive.
A curious fact may be noted here, that both nitro-glycerine and gun-cotton first found their use in the United States, but not as explosives. In 1847, Dr. Maynard, of Boston, dissolved guncotton in ether and alcohol, using the solution, collodion, for surgical purposes. One year later, nitro-glycerine was found to have a great stimulating effect on the heart, if injected in minute quantities, and was so used in medicine.
Nitro-glycerine was at first considered too violent to be used as an explosive, but experiments brought to light the fact that it congeals at 40° F. and while in that condition is practically safe, although it explodes violently by concussion when in an uncongealed state. It was not susceptible to fire, but its rate of explosion, not being under control, presented a serious objection to its use. It was with the use of gun-cotton and nitro-glycerine as bases that nearly all experiments were made in the development of smokeless powder.
A smokeless powder was first offered to the world in 186o by Col. Schultze of the Prussian army, who put out a semi-smokeless powder consisting of wood fibre cut into grains, purified, nitrated and finally impregnated with potassium nitrate or barium nitrate. This same powder was also manufactured by the American Wood Powder Company, but, when tried in rifles by the United States army, it was found to be worthless.
In 1866, Messrs. Prentice & Co. of Stowmarket, used a felt-like paper compound of gun-cotton and ordinary cotton for a charge, and at the same time Designolle and Brugere, in France, brought out a powder consisting of picrate of potash, saltpetre and charcoal, which was semi-smokeless, and which gave excellent results in the French chassepot rifle. In 1875 Spill patented a production of tubes for soluble and insoluble gun-cotton, and among various solvents he mentions ether and alcohol and nitrobenzine. We have here a forerunner of Prof. Monroe's indurite, which marked the beginning of the successful manufacture of smokeless powder in the United States.
Experiments continued along this line until 1888, when Alfred Nobel, a Swedish engineer, produced an explosive gelatine which resulted one year later in the manufacture of cordite.
In 1889 the first successful work was done by the U. S. Government, and the subsequent development of smokeless powder under the Ordnance Bureau of the navy will now be considered.
EARLY DEVELOPMENT IN THE NAVY.
The first smokeless powder used in the United States was fulminate of mercury, as its gases are practically transparent, and it is used to-day for the cartridges of the Flobert .22 calibre rifle. When tried for larger guns, however, it was entirely too violent, the rate of explosion not being under control.
The first work by the Navy Department began at the naval torpedo station in 1888, when Prof. C. E. Monroe produced indurite. Indurite is military gun-cotton purified by extraction with methyl alcohol, dried, gelatinized by mono-nitro-benzine, mixed, rolled, blocked, pressed and dried, after which it was placed in boiling water to remove the solvent. It was then cut into macaroni forms or flakes, depending upon the requirements. This powder was tried successfully, but was not adopted by the service, pending further development.
Various experiments were carried along, but the most important was a general analysis of all the gun-cotton on hand, which showed a great variation in the percentage of nitrogen. This proved that the texture of the cotton, the weather, the time of nitration, and a slight variation in the temperature or strength of the acid, all affected the final percentage of nitrogen.
In 1894, nitro-benzine as a solvent was replaced by acetic ether, and camphor was added as a deterrent.
The most important changes came in 1895, when Lieut. Bernadou and Prof. Brown began to blend the various lots of cotton to obtain a fixed percentage of nitrogen.
Acetic ether was replaced by acetone; selected lots of cotton were taken with reference to nitrogen; these were blended and barium and potassium nitrates and a precipitate of chalk were added to the blend to furnish oxygen. Camphor was omitted on account of its volatility.
It was then noticed that this acetone powder was very brittle, while the French powders were correspondingly tough. Acetone was then replaced by ether and alcohol as a solvent, and the result was that a much tougher powder was obtained. The next steps were in experimenting with nitro-cellulose and the method of purification and it was found that a soluble nitro-cellulose, containing as high as 12.8% of nitrogen, could be readily obtained.
Troisdorf powder had been found to be excellent, using nitrogen from 12.5% to 13% and using 2 parts of ether to one part of alcohol as a solvent. Barium nitrate was tried in the ether and alcohol solvent, but as it gave rise to smoke it was gradually reduced and finally done away with.
Prof. Mendeleef, (Russian), produced a pyro-collodion, the properties of which were:
1. Nitrogen uniform, and at 12.44 per cent.
2. Solvent: 3 parts ethyl alcohol; 1 part ethyl ether.
3. Heat test raised by washing with alcohol.
Lieut. Bernadou and Prof. Brown then experimented in making a powder on these lines.
A mixed acid was used, containing about 57% sulphuric, and about 28% nitric acids, the remaining 15% being water.
The initial temperature was atmospheric, the final about 400 C. secured by placing the nitrating pots in hot water. These were turned at the end of 35 minutes, making the total time of nitration 70 minutes. The cotton was then cooled and purified by Abel's method. The heat tests, however, came too low, only about ten minutes being obtained.
From this time forth, however, it was merely a question of perfecting the process, and this was done in the face of considerable opposition.
The pots were no longer turned; the time of nitration was gradually reduced to 60 minutes, then to 45 minutes, and finally to 30 minutes; a method was devised for utilizing the spent acid, materially decreasing the cost of manufacture; the duration of washing was diminished; and by increasing the proportion of mixed acid to the cotton, an increase of nitrogen-tetroxide, which causes fuming off, was avoided.
This leads up gradually to the process of manufacture of smokeless powder in use at the present day, which will be considered in detail.
MANUFACTURE.
The base of navy smokeless powder being gun-cotton, it is essential to first consider its manufacture, before proceeding with that of the powder.
The base of gun-cotton is pure cotton fibre, and this is usually obtained from white machined cop-waste.
It is possible to purify this waste in the factory, but at the present time there are several firms that purify cotton waste especially for the manufacture of gun-cotton, and it now proves just as cheap to buy the waste directly from these firms. It is furnished in bales of from 50 to 200 pounds.
PICKING AND DRYING.
This is a preliminary step to nitration. The cotton is extracted from a bale by hand, and then sent through a cotton picker. This picker consists of two iron rolls, revolving at a distance of about two inches from each other. On each roll are projecting teeth that pass just clear of each other as the roll revolves.
As the cotton is fed through the rolls it is torn and shredded between the teeth, thus separating the fibre and exposing a greater surface to nitration. The cotton is then spread out in trays and placed in an oven for drying. The capacity of these ovens varies from 50 to 100 pounds. This drying drives off any impurities and small particles that may remain in the fibre, and renders it more susceptible to nitration. The cotton is allowed to remain in the ovens for four hours with the temperature 100° F. and is then placed into air tight tanks and removed to the nitrating house.
NITRATION.
There are two general systems of nitration—the pot system and that of the nitrating centrifugal. As the pot system is more expensive, and very susceptible to fires, it is not regarded with favor, and only the nitrating centrifugal will be considered.
In this system 16 pounds of cotton are usually dipped at a time, (this quantity depending upon the size of the machine used), into a solution of concentrated nitric and sulphuric acids. The strength of this mixed acid varies with the percentage of nitrogen desired. To obtain a cotton having from 12.4 to 12.8 per cent. Of nitrogen, the strength of the acid is: sulphuric, about 56.5%; and nitric, about 28.2%, the remainder being water. The weight of the acid used for 16 pounds of cotton is 9oo pounds.
At most powder works the average time of nitration varies between 25 and 35 minutes, depending upon the dampness of the atmosphere. The acid solution is kept at a temperature of 30° C. Great care must be taken not to exceed this temperature more than one or two degrees, otherwise there will be a fume off, the nitric acid breaking down and giving off reddish brown fumes. In case this heat is generated by the action of a drop of moisture on the sulphuric acid, it can be reduced by at once forking the heated portion under the surface of the solution. Care must be taken that no moisture falls upon the cotton after the acid has been wrung off, and before the charge has been removed to the drowning tank, for this will usually result in a fume off, and the 16 pounds of cotton will be reduced to a worthless charred mass.
An earthenware flue and an exhaust fan carry off the fumes arising from the ordinary process of nitration.
At the International Powder Works, the time of nitration has been reduced to Is minutes. This is done by increasing the strength of the nitric acid, but as the danger of fuming off is somewhat increased, unless great care is observed, the time gained is lost.
After the charge has been nitrated the acid is wrung off by means of revolving the centrifugal, and the cotton is forked over into a drowning tank, where some of the free acid is drowned out; after which the cotton is placed into wringer and wrung out, while a hose assists in washing away the exposed free acid. The cotton is then placed into bins until a sufficient quantity is ready for boiling.
The succeeding steps, boiling, pulping and poaching, are merely steps for the purification of the nitrated cotton, to get rid of all particles of free acid and impurities, in order to make the heat test as high as possible.
BOILING.
As the capacity of the pulper, usually about 500 pounds, is a convenient unit for a lot of pyro-cellulose, two boiling tubs should be used each holding 5oo pounds. These tubs should be fitted with feed and drain pipes for water, and also a steam pipe for heating. A flue should be fitted from the top of the tubs to carry off the vapor.
The cotton is boiled for three periods of two hours each, at 100° C. the water being changed at the end of each two hours. Fresh cold water is then run in and drained off, washing the cotton, which is then transported to the pulping house in cars.
PULPING.
In pulping, the cotton is placed in cold water, and forced by means of paddles, to pass between moving knife blades which cut and shred the cotton, thus rendering it possible to wash out any of the impurities that may remain within the fibre itself.
The process of pulping takes from 5 to 15 hours, depending upon the texture of the cotton and the steam pressure, and the only way to tell when the charge is sufficiently pulped is by handling it. An experienced man can tell at once by the feel of the cotton if it has been properly divided and chopped up.
During the pulping the solution should be kept alkaline by the addition of soda. The water should be constantly changing. A pump, fitted with a washer of brass wire to prevent the cotton getting through, can draw off the surface water, which is replaced by fresh feed water on the opposite side of the pulper. After the pulping is complete, the charge is run by gravity to the poachers.
POACHING.
The poaching tubs should have the same capacity as the pulper, i. e., 500 pounds. In these tubs a paddle or a propellor, driven by a small engine, constantly agitates the cotton and water, which mixture is kept at the boiling point. As the cotton is heavy and sinks to the bottom of the tub, a propellor at the bottom, driven by a vertical shaft, will be found preferable to Abel's side wheel paddle, which does not thoroughly agitate the bottom of the pulp. The poaching covers a period of 12 hours in boiling water, but experiment has shown that better results are obtained by subdividing this 12 hours, and washing the cotton with cold water between the divisions.
Different sub-divisions are used at the various factories, but seemingly the best results have been obtained by using periods of 6 hours, 3 hours, and 3 hours duration, with 3 washings of cold water between periods. At the end, the charge is given 12 washings with cold water, after which it is given the test for stability. The charge is allowed to remain in the poacher until the stability test has been completed, because, if it fails to meet the requirements, the lot must be retreated.
STABILITY TEST.
To make this test, the pulp is skimmed with an agate dipper and sent to the laboratory in a quart bottle. Here it is poured into a piece of clean cheese cloth, and put into a small fruit press where as much water as possible is squeezed out.
The remaining cake of cotton is then broken up by hand and put on a paper tray, and placed in a drying oven, where it is heated from 5 to 6 hours at 43° C. It is then taken out and allowed to stand in the air to take on moisture, from 1.5 to 2% being desired. Twenty grains are then weighed out and placed in a test tube 5 1/2 inches long, and 5/8 inches in diameter. The pyro is then pressed down in the tube to occupy a space of about 1 5/8 inches; and the remaining dust and particles removed from the sides of the tube.
A strip of potassium-iodide-starch paper, 1 inch by 3/8 inches is then moistened by a drop of glycerine solution, and suspended in the tube by a platinum hook. The tube is then inserted in a bath heated to 65.5° C.
The required stability test is 30 minutes, but it is very advantageous to exceed this by 5 minutes is possible.
When the pyro decomposes, a dark brown line is formed at the junction of the moistened and dried portions of the test paper. The action is as follows:
HNO2 is liberated by the heat. KI + HNO2 = KNO2 + HI.
But as the hydroiodic acid (HI) is unstable, it breaks up further liberating iodine.
2HI+O = H2O+I2
The free iodine then unites with the starch making the brown line. This last is not a chemical reaction and its formula is not known. If this line appears before 30 minutes after the tube was inserted in.the bath, the test fails and the lot must be repoached.
If the time exceeds 30 minutes the test is successful. In case a number of drops of moisture collect on the sides of the tube, the pyro has too much moisture in it and the test is useless. In this case the pyro must be redried.
WRINGING.
After the stability test is successful, the cotton is allowed to run by gravity directly into a centrifugal wringer, which revolves at a very high rate of speed, and the cotton is wrung out as dry as possible. After this wringing it contains about 25 to 30% of moisture, and is then placed into boxes ready for dehydration, the preliminary step to the manufacture of the powder.
DEHYDRATION.
As stated, after leaving the centrifugal wringer the cotton contains from 25% to 30% of moisture, and in the manufacture of smokeless powder it is necessary to drive out this moisture and replace it by the solvent. A dehydrating press is used to accomplish this.
A charge of 44 pounds is weighed out, which is equivalent to about 33 pounds of dry pyro. The press is provided with two pistons, the head being grooved in the lower one to permit the water to escape. The lower piston is run up, the charge is placed in the cylinder, and the upper piston is run down at a pressure of 200 pounds per square inch.
Alcohol, equal in weight to the weight of the dry pyro, is then run in on top, an air cap is placed on the top of the cylinder and held down by the upper piston, and the alcohol is forced through the cotton by means of air pressure at about 100 pounds per square inch. The dividing line between the alcohol and water can be readily told, and the pure alcohol saved. A distilling plant recovers the dilute alcohol.
The cap is then taken off the cylinder and the whole mass of cotton subjected for about two minutes to a pressure of 2000 pounds per square inch. The resulting block is then taken from the cylinder and contains about 25% of alcohol, and less than .5% of water. As our formula for colloiding is 1 part of alcohol to 2 parts of ether, it becomes necessary to only add ether equal to half the weight of the block, and the pyro is ready for mixing.
MANUFACTURE OF POWDER.
As the subsequent steps in the manufacture of powder are of short duration, and require but little description, they will be considered as a whole rather than singly.
The block of pyro, containing about 25% of alcohol, is taken to the mixing room and broken up by hand into the mixer; and 50% of ether is then added. The whole mass is then thoroughly mixed and pulped by means of two revolving cork screws, which turn in opposite directions. This is continued for from 1 1/2 to 2 hours, the direction of turning of the screws being frequently reversed, until the whole mass is thoroughly mixed. It should then be soft and mealy to the feel.
It is then taken out and run through the strainer press to remove any small hard lumps that may remain after mixing.
It may be noted here that sometimes the mixings are so clear that no straining whatever is required, while at other times the same brand of cotton shows many lumps, and straining is absolutely necessary. This can be accounted for solely by a difference in the texture of the cotton fibre.
After straining, the pulp is taken in tanks to the block or moulding presses, where it is pressed into cylindrical blocks about 6 inches long and 3.5 inches in diameter.
These in turn are taken to the die press room, and run through dies depending upon the calibre of the powder desired.
Flat ribbons are run out for flake powder, and circular multiperforated cords for all powder higher than one-pounder.
These cords are cut off in suitable lengths by the press boys, while the ribbon powder is rolled up on reels. The powder is then cut as desired by an automatic chopper.
After cutting, the multi-perforated powder is ready to be put in the dry house at once; but the flake powder must first be sifted and dusted, due to the fine dust and imperfect flakes that collect in it.
The powder is then transported to the dry houses, where it is spread out on trays to dry. The dry houses are kept at a temperature of from 95° to 105° F. but the time of drying depends to a large extent upon the weather.
TEST FOR VOLATILES.
It now becomes necessary to determine when the powder has been dried sufficiently to give the required ballistic results, as this drying is one of the most important steps in the development of smokeless powder. The powder must not be so excessively dry that the pressure developed will exceed that allowed for the gun; nor, on the other hand, can it have such a high percentage of volatiles that it will dry out on board ship, and thus become a quicker powder. The mean between these two positions has only been determined after a careful consideration and study of all the accumulated ballistic data.
Experiment has shown us the maximum thickness of web which will be entirely burned, for any given length of gun. With this known web thickness of the powder, it was then dried down to as low a percentage of volatiles as possible to give the required velocity and pressure, and numerous experiments soon gave sufficient data to construct a curve which would show at once the total volatiles necessary to give the ballistic requirements.
This will be seen from the portion of the curve shown—the ordinates representing the web thickness, the abscissa2 total volatiles, and the curve the required ballistic result.
Once determined by experiment, the thickness of web to be entirely consumed can be calculated for any powder as follows:
For grains of 7 perforations: T = (D – 3d)/4 + D/10
For grains of 1 perforation: T = (D – d)/4
For flake powder T .= Thickness of strip.
To determine the percentage of volatiles.
After the powder has dried down for about the length of time deemed sufficient, a sample is taken from the lot and sent to the laboratory for test. This is cut into slices about .02 inches thick, and a known weight is placed in a glass dessicator, in the bottom of which is calcium-chloride,—CA CL2. It is allowed to remain here for 48 hours and is then taken out and reweighed. The loss of weight is considered moisture. Usually about 2.5 grammes is taken for this test.
The remaining powder, after the loss of moisture, is then placed in a drying oven and heated for 5 hours at 800 C. and the new loss of weight is considered solvent.
The total loss of weight from the moisture and solvent is the total volatiles of the powder.
In case it is desired to obtain the total volatiles approximately the powder is not placed in a dessicator, but is placed in the drying oven at once and heated for 5 hours at 800 C.
Sufficient moisture is driven off by this drying that the total loss of weight can be considered as the approximate total volatiles.
The precipitation method is another way of obtaining the total volatiles. This method requires time and constant attention and as its results are not any more accurate than the above method, it is seldom used.
In this method, a certain known weight of powder is dissolved in ether and alcohol, the solution poured into water. The ether and alcohol start to escape, and can be readily boiled off. The residue is then dried down and carefully reweighed.
The loss of weight is considered the total volatiles.
BALLISTIC TEST.
After the powder has been dried down to the percentage of volatiles desired, a firing sample is taken out, and the remainder is taken to the magazine and stored in air tight boxes marked with the number of the lot. The firing sample is taken to the firing range for ballistic test.
Assuming the case of 6-pdr. powder,—the ballistic requirements are: 2250 feet per second in velocity, and the pressure not to exceed 13.5 tons. The charge, owing to the capacity of the cartridge case, cannot exceed 610 grammes, but the less powder required the better. The velocity is obtained by means of a set of firing screens and a chronograph; the pressure being obtained by a pressure gauge and disc, which is placed in the cartridge case at the base when the charge is made up. Chronograph tables and a pressure curve enable us to get the result from the test.
At least three shots should be fired, starting with a small charge and increasing it until the required ballistic result is obtained. If the requirements are fulfilled the powder is accepted and the lot is put aside for the general blend. If the velocity falls short for a charge of 610 grammes, it is usually found that the powder is not dry enough, and the lot is placed in the dry house and dried down to a lower per cent of volatiles and tried again.
If the pressure exceeds 13.5 tons, as it frequently does in powders of high nitrogen, it is usually on account of excessive dryness. It has been found that in the presence of moisture the pressure falls much faster than the velocity, and the best way known at present to reduce the pressure is to allow the powder to take on a small per cent of moisture.
Of late, however, the bureau is discouraging this practice, as they are requiring very dry powders, due to reports that powders frequently dry out on board ship and so cause higher pressures than those obtained when the powder was tested.
This necessitates a quick burning powder with a low nitrogen, and still one that will give the required velocity. This is not an easy thing to obtain, and it can only be done by exercising great care with the web thickness in manufacture, and also with the total volatiles obtained in the dry house.
BLENDING.
When sufficient powder is assembled, a general blend is made so that the entire lot will be uniform. Boxes from each lot are opened and a like amount taken from each and placed in a cylindrical blender. A few turns of this is sufficient to thoroughly mix the lot, and it is then taken out and stored permanently in the new standard powder boxes ready for shipment.
It is well to have the two ends of the blending cylinder connected to the earth by a copper wire, for in turning, the grains in running over each other generate a certain amount of static electricity, which in some cases has been sufficient to cause an explosion. After the blend has been completed, an index number is assigned to it by the bureau and it is then shipped to one of the naval powder magazines where it is kept until ready for issue to the service as needed.
HEAT TEST OF SMOKELESS POWDER.
In the heat test of smokeless powder there is a preliminary test for powder that has been stored in magazines, which will give an idea as to whether or not the powder is starting to decompose. This preliminary test is embodied in bureau of ordnance letter No. 9928 of December 13, 1902.
Small samples of the different powders stored in magazines are kept in glass bottles and a piece of litmus paper is kept in each bottle. This litmus paper is changed every week and inspected twice daily, and will show any special signs of decomposition. In the preliminary test the sample of powder in the whole grain is placed in a glass stoppered bottle, one day before the regular test is to be made. This is tested by placing a strip of potassium iodide paper, 2 inches by 1 inch, moistened with a large drop of glycerine solution, about the size of a cent. This is kept in the bottle for a period of one hour, and no signs of discoloration should show on the paper.
In the regular heat test, flake powder is not cut. Strip or multi-perforated powder is cut into shavings about .002 inches thick and these are put on watch glasses and placed in a drying oven and dried for 48 hours at a temperature not exceeding 43° C. The sample is then exposed to the air until sufficient moisture is taken on for the test: over night will be sufficient. Twenty grains are then weighed out and placed in a test tube. The remainder of the test is similar to the test for pyro-cellulose. The sides of the tube are rubbed clean; a strip of potassium iodide paper fastened to a platinum hook is then moistened with a drop of glycerine solution and inserted into the tube. The bath is kept at a constant temperature of 65.5° C. and the time of insertion is noted. The line of demarkation between the wet and dry portions of the paper is kept even with the line of moisture that will appear on the inside of the tube. If the least brownish discoloration appears at the line of demarcation the time is noted at once. If no discoloration appears at the end of 40 minutes, the test is discontinued and marked 40 minutes plus. Care should be taken to conduct the test where as good a light as is obtainable will show on the paper. The minimum test that is allowed for smokeless powder is 40 minutes at 65.5° C.
PREPARATION OF TEST PAPER AND GLYCERINE SOLUTION.
In the preparation of potassium-iodide-starch paper, especially pure filter paper is washed with distilled water and dried. It is then cut into strips 6 inches to 8 inches wide and dipped into a solution of potassium-iodide and starch for about 8 to 10 seconds, and then hung up to dry in the dark. Light affects the chemical properties of the paper if exposed for any great length of time.
The solution of potassium-iodide and starch is made as follows: 15 grains of potassium-iodide is disolved in 8 ounces of water, 45 grains of corn-starch is stirred up in water and boiled. The two solutions are then mixed and allowed to cool. The glycerine solution in the heat test is made of equal parts of chemically pure glycerine and distilled water.
Heat test outfits, containing all the necessary apparatus for conducting the test, and a drying oven, are furnished by the torpedo station to all navy yards and to all vessels in the service.
MANUFACTURE OF GUN-COTTON AND FULMINATE OF MERCURY.
A word might be said here as to the manufacture of gun-cotton and fulminate of mercury, as both come under the class of smokeless explosives.
The manufacture of gun-cotton differs but slightly from the manufacture of pyro-cellulose as already explained. The principal difference is in the strength of the acid used.
A cold mixed acid of about 70° F. is used, and the percentages are: about 73% of H2SO; about 22% HNO3; and about 5% H20. The cotton is nitrated in this solution for about 24 hours, and was formerly done by the pot system, although the nitrating centrifugal is now used. The purification process and the stability test are exactly the same as for pyro-cellulose.
After the stability test the pulp is not wrung out, but is run from the poacher into a small tank and stirred up with a screw paddle. A mixture of pulp and water is then run into a preliminary press and subjected to a pressure of 100 to 200 pounds per square inch. This gives a block of about 6o% moisture. This block is taken to a final press and subjected to a pressure of about 2000 pounds per square inch and when taken out contains about 14 to 15 per cent moisture. The block is then put into a pail of water and allowed to increase in weight until it contains about 25 per cent moisture, which is the navy standard. The completed gun-cotton contains from 13.1% to 13.5% of nitrogen.
A die in the final press stamps on the block the place and date of manufacture, and the number of the lot, so that a history of the cotton can be kept and if any one part shows signs of decomposition, the whole lot can be traced and destroyed.
Wet gun-cotton is exploded by means of dry gun-cotton; by a sympathetic explosion of one part of wet gun-cotton near another, and occasionally by the explosion of dynamite in the vicinity, although gun-cotton explosion will not detonate dynamite. Wet gun-cotton is regarded as the safest explosive known.
FULMINATE OF MERCURY.
Fulminate of mercury is perhaps the most dangerous explosive known. In its manufacture, nitric acid is reduced by the addition of water to a specific gravity of 1.37.
One part of mercury by weight is dissolved in 12 parts of nitric acid by weight. When dissolved this is put into a lukewarm solution of 11 parts of alcohol and allowed to act.
Bubbles of gas are given off, together with white fumes which eventually turn red. As the action is completed, the fulminate settles to the bottom as a greyish black powder precipitate.
The solution, precipitate and all, is poured into a large vessel and washed repeatedly with water until no acid reaction is obtained. It is then stored away for use, the fulminate being kept under water. In winter a bit of alcohol is added to keep the solution from freezing.
Fulminate of mercury is exploded by means of percussion, by heat, and by strong sulphuric acid. Thirty-five grains are used in a detonator or exploder, and about .4 grains is put into a primer cap. In loading an exploder or detonator, the fulminate is first removed from water and dried in a steam oven of 40° C. for a period of from five to seven days until thoroughly dry, and then loaded into the fulminate case.
SPECIAL REGULATIONS FOR SMOKELESS POWDER.
Special rules for the care of smokeless powder on board ship and in magazines have been issued by the department.
These rules are of sufficient importance to be noted.
1. A sample of each lot of accepted powder is kept in the factory, and frequently observed and tested. The bureau is informed at once of any deterioration.
2. A sample of each lot of powder in the magazine is given the prescribed heat test once every 3 months.
3. All smokeless powder is to be stored away from the direct rays of the sun.
4. Samples of each lot are to be kept in glass stoppered bottles and inspected twice daily.
5. All magazines are to be inspected twice daily.
6. No fixed ammunition containing fulminate primers is to be stored in any smokeless powder magazine.
7. Black powder must not be stored in the same magazine with brown or smokeless powder, except where it forms the ignition charge of prepared ammunition.
8. No oakum, waste, rags or any oily matter are to be allowed in a smokeless powder magazine or loading room.
9. Gun-cotton should never be stored near smokeless powder.
SUMMARY AND DISCUSSION.
It remains to discuss the existing conditions of smokeless powder in our service, for too much cannot be said in its favor, and against those who have done so much to hinder its advancement. Its advantages are most apparent, and it seems as essential to provide the gun captain with an unobscured vision in firing as it is to provide him with modern ordnance. The extra cost in the manufacture of smokeless powder is practically made up in that a much less charge of it is needed to give the required ballistic results.
For the small arm, its greatest advantage, aside from the higher velocities obtained, is that is does not disclose the position of the marksman, a thing invaluable to the scout and skirmisher. As for its use in rapid fire guns and guns of larger calibre, how well will it be recalled in the Santiago blockade and bombardments the necessity of waiting frequently for 2 or 3 minutes until the dense clouds of smoke were blown away. And with what envy did we look upon the New Orleans, as she fired continuously, with no interruptions on the account of smoke.
A word may be said here in connection with the recent mishap to the Iowa's 12-inch gun. To those interested in the future welfare of smokeless powder it seems incredible that this accident should have been laid to the smokeless powder charge.
If a rubber band is guaranteed to be stretched to its elastic limit 100 times, and it is stretched 200 times and breaks on the 201st stretching fault can hardly be found with the stretching agent. Yet this is exactly what was done in the case of the Iowa's gun. That unequal pressure waves were developed in the bore by the explosion of the charge is something of which no one can be even reasonably certain, and no satisfactory evidence can be shown to that end. Similar charges of the same powder will developed an almost constant pressure ninety-nine times out of a hundred
How very much more probable then, that the gun, having been used far beyond its allotted life of usefulness, developed a weak spot and burst of its own weakness.
Smokeless powder is no longer an experiment but an accomplished fact, and its rate of burning and the pressure developed are under absolute control.
To its disadvantage it may be said that it requires great care in preservation, but care should always be taken in the handling of explosives. Especial care is necessary in making the heat test and the directions accompanying each outfit should be carried out to the letter.
Shortly after the destruction of a large quantities of smokeless powder on board the U. S. S. Olympia, a series of experiments was conducted under my observation with the view of showing that the powder in question might not have been in actual state of decomposition.
The potassium-iodide-starch paper, when moistened with the drop of glycerine solution, will show a slight but distinctively noticeable brownish line when acted upon by alcohol vapor. As the total volatiles of powder seldom goes below 1.5 under service conditions, this will include a small portion of the alcohol solvent, and unless the directions for drying the sample for 48 hours at 43° C. are carefully carried out there is a good possibility that a small portion of the solvent may remain in the powder. When inserted in the bath at 65.5° C. this remaining solvent will be driven off almost immediately, and the alcohol vapor acting on the test paper will give a slight brownish line, and cause those who are unfamiliar with the test to assume that the powder is decomposing. By taking the cork from the tube these alcohol fumes can be detected at once by their odor, and this should dispel any doubts. The brown line due to decomposing powder is much more distinct than that made by alcohol vapor, but their similarity is sufficient to necessitate great care in making the test, and too much experience cannot be obtained.
It would be a most excellent plan, and a very profitable one to the navy department, if every ordnance officer in the service was given a special powder course of instruction at the torpedo station before being assigned to ordnance duty on board ship. With smokeless powder plants at Indian Head and the torpedo station, officers sent to these places would have an excellent opportunity of becoming familiar with its manufacture and care.
There is much room for improvement and advancement in the process of manufacture, and the quality of the powder resulting, but the advantages of smokeless powder are so great that the extra care required with it is not worthy of consideration, and we can but hope that its progress in the future will be even greater than that of the past.
With this object in view, the unceasing efforts of the officers engaged in the development of smokeless powder should meet with the greatest encouragement from the entire service, and the time will soon arrive when we can point with pride to the U. S. Navy smokeless powder as being without an equal as an explosive for modern ordnance.