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into the grand total of 1904 millions of dollars given as the Liverpool received the visitors in the Town Hall on value of the mineral productions of the United States. Wednesday evening. Meetings were held for the reading The same is true of every other metal on the list; in some and discussion of papers on Tuesday and Wednesday cases, notably, perhaps, in that of aluminium, the value mornings in the Municipal Central Technical School. of the metallic product is many times greater than that Brief extracts from these are subjoined. of the mineral from which it is produced ; thus the value Locomotives designed and built at Horwich were deof the aluminium produced is given as 5 million dollars, scribed in a paper by Mr. George Hughes, who is the whilst that of the bauxite from which it is produced is chief mechanical engineer of the Lancashire and Yorkabout 450,000 dollars ; surely it is the latter figure, and shire Railway. This company possesses 1517 locomotives, not the former, that should enter into a list of the values of which there are about 1100 in daily use. When the of the mineral productions of any country.
works at Horwich were opened, Mr. Aspinall, president In the non-metallic products similar anomalies are also to of the institution, and at that time chief mechanical be met with ; cement, bricks, oilstones and millstones are engineer, resolved introduce standardisation and, articles that owe a very great, if not in every case the wherever possible, interchangeability. Joy's valve gear greater, part of their value to the labour, fuel, and power was adopted, as it was found that the mileage between used in their preparation rather than to the crude material repairs was greater, and also that there was a slight from which they are produced; if an American sculptor economy in coal per engine-mile. carves a statue out of native marble, should the value of Among other types of locomotives described it is of the finished statue be included in the sum total of the value interest to note six engines which were fitted in 1902 with of the mineral resources? There can only be one answer Druitt-Halpin thermal storage tanks. Where stopping to such a reductio ad absurdum, and yet the principle is places are frequent on rising gradients there is distinct exactly the same as that of including the value of the economy. Certain tests carried out between Salford and dressed grindstones instead of that of the sandstone or Accrington resulted in a saving of one ton of water, and grit from which they are cut.
under similar conditions elsewhere the saving was 12 per The above are matters of principle which present, no
On other sections of the line, which are not so doubt, great difficulties in arriving at a satisfactory solu- favourable, the all-round economy of these engines is tion; the coordination of the methods of tabulating the brought down to 4 per cent. mineral productions of different countries, so as to admit A four-cylinder passenger and express goods engine, of just comparison, has often been tried, but has never built to the author's designs in June, 1908, is also of been attained successfully yet, so that all that statisticians interest. Absolutely perfect balancing could have been can do is to take care that they thoroughly understand achieved without the aid of balance weights if the crank the differences that obtain between the various systems in angles, the disposition of the cylinders, and the weights vogue. In other respects the present volumes are quite up of the reciprocating parts had been arranged to neutralise to the high standard that we have been accustomed to in amongst themselves the reciprocating disturbing forces; the United States Geological Survey publications. As then, by balancing the revolving masses, the variations of already said, they suffer from want of compression, and rail load and the horizontal swaying couple would have there are many repetitions that might be avoided and much disappeared. Excepting for a slight vertical component superfluous matter that might well be excised. In fact, produced by the obliquity of the connecting-rod, the engine they require more careful editing than they receive at would then have been perfectly balanced. This arrangepresent, and this is all the more necessary seeing that the ment, known as the Yarrow-Schlick-Tweedy system, would different articles are written by different contributors, and have involved an independent set of valve gear for each are of very unequal value.
cylinder. Actually, the cranks were arranged in pairs at For example, no careful editor would pass such state- about 180° apart respectively, and the reciprocating ments as we find under the item fuorspar, where we are masses, being made equal in weight, balance each other. told that the mineral is “only slightly harder than The masses of the connecting-rods were divided between calcite, and consequently crushes easily," whereas the ease the rotating and reciprocating masses as suggested by or difficulty of crushing has nothing to do with hardness; Prof. Dalby, and the revolving masses were balanced by and again, "When Auorspar is associated with zinc- revolving balance weights. This engine is a very steady blende, complete separation of the two ininerals has been and smooth-running machine. difficult on account of their nearness in specific gravity "; The discussion centred round the important questions of the specific gravity of fluorspar is about 3.1, and that boiler deterioration, corrosion, and priming. Mr. Hurry of blende about 4, a difference which should afford an Riches expressed the opinion that the best way of avoid. ample margin for successful separation in a suitable | ing troubles due to the nature of the feed-water is to appliance.
remove the impurities before feeding into the boiler; it Finally, it may be pointed out that although these is, however, inadvisable to reduce the hardness of feedvolumes in their final form may be considered somewhat water below 6o. belated, no serious inconvenience results therefrom, as the A paper on reinforced concrete was contributed by Mr. wise precaution is taken of issuing the various sections in Arthur C. Auden, of the firm of Messrs. William Cubitt pamphlet form as soon as possible after the end of the and Co. Reinforced concrete is by no means a new thing; year to which they refer, an advance sheet of statistics it has passed the experimental stage, as is evidenced by being; moreover, issued usually with considerable rapidity. important structures erected in London in 1889, and still This is a procedure that might well be imitated with great
On the Continent equally large structures exist advantage by a good many other nations, our own not which are now twenty-five years old, and have never been excepted.
Henry Louis. strengthened or patched. Failures have occurred through
bad design or workmanship, but the proportion of these
is small. The cost of the proposed structure is affected THE INSTITUTION OF MECHANICAL by the cost of its constituents, and these in turn by the ENGINEERS.
cost of freight and carriage. Hence the author briefly
classifies the materials, and gives useful hints on the THE summer meeting of the Institution of Mechanical properties of each.
Engineers opened at Liverpool on Tuesday, July 27. For aggregates, the eastern counties' flint is often the The president, Mr. John A. F. Aspinall, and the council only stone available locally. Good, tough concrete can be and members of the institution, were welcomed in the made with this, but is untrustworthy for fire-resisting purlecture hall of the Municipal Central Technical School by poses, owing to its tendency to crack and fly" under the Lord Mayor of Liverpool, Councillor H. Chaloner heat. This tendency can be much reduced by first crushDowdall, and the members of the Liverpool reception ing all the stones. The same remarks apply to limestone, committee. The importance of Liverpool as an engineer- a material which is not more fire-resisting after being ing centre secured an attendance of nearly 500 members, broken. As it is apt to disintegrate to powder under the who participated in the excellent arrangements made re- action of heat, it is inadvisable to use this material where garding visits to works and excursions. The institution fire-resistance is an important consideration. Limestone dinner was held in the Exchange Station Hotel on Tuesday always requires washing before use to get rid of the fine evening, and the Lord Mayor and Lady Mayoress of dust which covers it and prevents the cement properly bonding with it. Sandstone, as a rule, is too soft, porous, Maginnis naturally devotes a great deal of his space to and absorbent for use in reinforced-concrete work. It the marine steam turbine. · While the use of turbines has may be safely used if it will stand about i} tons per produced practically no advance or improvement in fed square inch under a crushing test, and also if the differ- consumption since 1901,' still, an advance has to be reence in weight when clean and dry, and after being two corded in that a greater speed has been attained. During days under water, does not exceed 8 per cent. Quartzite the past eight years experience has shown the trustworth. stone is fairly good, if not too soft and open in texture, ness of the Parsons turbine machinery. Notwithstanding in which case the same precautions apply as for sand- that there are now more than seventy steamers continustone. It should be noted that the test pieces for crush-ously, plying to and fro, no sailing schedules have been ing tests should have an area of at least 10 inches or upset by a failure of machinery, nor has a turbine steamer 12 inches..
ever had to be · towed into port. The author · has .no With reference to artificially. produced aggregates, hesitation in stating that rotary machinery must eventually broken earthenware and stoneware from the Potteries replace the present system in cargo steamers as well as district make a good aggregate, but these must be un- in liners: glazed, as the glaze prevents the proper adhesion of the Combined systems of reciprocating and turbine machinery cement. Burnt clay and gault may be used provided they were referred to, but the author does not think that an are tough and hard, and do not soften or crumble after extensive adoption of this system will be made. being left in water for two or three days. In general, evidence of the saving in weight in the boilers where broken bricks are not a good aggregate for reinforced turbines are installed, owing to the lower steam pressure concrete. They may be employed safely if hard and close which may be used, the author states that in the case of in texture and free from mortar. Coke-breeze is cheap the Lusitania and Mauretania the saving in weight on the and readily obtained, but cannot be regarded as being boilers alone is about 120 tons over and above that which really fire-proof. The effect of any sulphur present must would have been required if triple or quadruple piston also be considered. Ashes and clinkers may be used. In engines had been used. the case of ashes, only those which will float in water The author gives a summary of the results attained by and are of uniform colour and texture, as well as being marine engineering to date as follows :—vessels of clos quite free from coal and dirt, should be used. Really upon 800 feet length and more than 38,000 tons dishard and clean clinker alone is serviceable. In both of placement are being propelled across the Atlantic at an these sulphur must be considered. Slag from blast average speed of 25) knots by turbine machinery work. furnaces and cupolas makes a good aggregate if hard, ing up to about 70,000 horse-power, having a consumptough, and free from dust; any sulphur present must be tion of upwards of 1000 tons per day. Similar resul:s noted.
have been obtained in the turbine-propelled warship Sulphur is apt to attack the reinforcing steel with Indomitable, of more than 40,000 horse-power, and maindisastrous results. The maximum allowable percentage of tained across the Atlantic with water-tube boilers. sulphur in reinforced concrete aggregates is now being The electrical operation of textile factories formed the made the subject of experiments, and it is hoped an subject of a paper by Mr. Herbert W. Wilson. The prinauthoritative statement will soon be made. In the form cipal advantage claimed lies in the fact that a much of a sulphate sulphur is practically harmless, but is very greater steadiness of drive can be obtained, with consedeleterious if in the forın of a sulphide.
quent higher average speed and increased output. Slight It is of importance that no free lime be present in variations in speed above that corresponding to the maxiartificial aggregates ; carbonate of lime is practically harm- mum safe tension breaks the threads, and unless absoless. Washing and exposure to the air and sun will do lutely constant speed can be obtained, it is necessary much to convert sulphides into sulphates and free lime into to allow a margin of safety and to
a speed carbonates. Good and accessible aggregates are often con- materially below the breaking point.
case in demned because no discretion is exercised as to the form Lancashire, with two mills under the same management in which lime and sulphur occur.
and of about the sine size, and working under the same A certain amount of sand is absolutely necessary in general conditions, the results obtained from the electrically concrete, and no other material is at present known which driven factory have been distinctly superior to those from can be substituted for it. Generally speaking, the better the mechanically driven one. The improvement in the a sand is for moulding purposes the worse it is for re- quality of yarn was so noticeable that the output from the inforced concrete. Dirt in the form of slime, mud, or electrically driven mill fetched a distinctly better price than vegetable refuse is bad, but a little loam, enough to soil that from the other factory, the increase being stated at the fingers, but not enough to cause the sand to adhere about 2 per cent. As regards increase in production, to them, is no detriment. Small particles or nodules of mills in this country which have adopted electrical driving clay do not appear to affect the strength of the concrete, may be estimated as showing an improvement of 5 per but it is better to avoid them if possible. It is not good practice to use the stone aggregate, and its smalls and A paper on the indicating of gas engines was contributed dust, together with some sand, upon the chance that they by Prof. F. W. Burstall, of Birmingham University. The will be in proper proportion, and that the voids and spaces Standards Committee of the Institution of Civil Engineers will be properly filled. Such a practice should not be expressed the opinion in their 1906 report that the inallowed in reinforced work, where absolute homogeneity dicating of gas engines was open to very much greater is so essential.
errors than was the case with steam engines, and this With reference to cement, any user is safe if he insists matter has been considered by the Research Committee of that his cement shall pass the British standard specifica- the Institution of Mechanical Engineers. In the tests tion in every detail, and purchases from a trustworthy undertaken by the author, two indicators were used maker. It should not be one of the many mixtures
simultaneously, one of the ordinary string type and the imported into this country as cement, which do not deserve other an optical indicator. A Premier gas engine was the name, and are costly at any price.
used having a cylinder 16 inches in diameter by 24 inches Methods of inserting the reinforcement in beams, slabs, stroke, running at 165 revolutions per minute. The only columns, &c., together with hints on erecting various
variation in the four tests recorded was the amount of structures, take up the remainder of this valuable paper. gas admitted. the mein pressure varying from 53 kg. per
Prof. Unwin spoke of reinforced concrete construction cm.? up to about 71 kg. per cm. as demanding excellent execution and supervision to be
The string indicator emploved was of the Crosby_type, successful. In regard to formula of the empirical class.
selected for these tests by the Crosby Company. Before largely employed in this subiect, the range of experimental and after each set of trials the indicator was tested for work should rule the trustworthiness of the formulæ. backlash and friction, and the spring also calibrated. Much of the present methods of design is based on guess
The backlash was in all cases negligible, and the friction work. He took the opportunity of urging the necessity
amounted to less than 1 lb. with a spring having a scale for more extended experiments.
of 100 lb. per square inch. The optic indicator was lent In presenting his paper on the advance of marine by Prof. Hopkinson, and was calibrated at the University. engineering in the early twentieth century, Mr. Arthur J.
Both indicators were mounted on a branch piece con
nected to the engine cylinder, and the indicator diagrams Mr. Haldane said he had made up his mind that there were taken simultaneously. The indicator barrel of the could be no real progress unless we proceed scientifically Crosby indicator was rotated by phosphor-bronze and in order—that is to say, unless we are perfectly clear stranded wire wound round the barrel and led to a bell- | about what we want, as to the structure of the machines crank lever. The bell-crank lever was driven by a steel wire which will be used for the purposes in view, and the proattached to the usual lever driven by the engine piston. duction of them in a way which should be at least A very heavy spring, in which a compression of 400 lb. effective. The first thing done was to ask the Committee produced a contraction of 2 inches, controlled the bell- of Imperial Defence to investigate this question and to crank lever. The optic indicator was also driven by means discuss it with the technical subcommittee. The report of a phosphor-bronze stranded wire.
was to the effect that the class of machines must be The mean diagrams were prepared from no fewer than divided into three heads :-rigid dirigibles, non-rigid twelve individual diagrams, each being divided by the dirigibles, and aëroplanes. For naval purposes the rigid method of ordinates, and the heights read by an accurate dirigible is probably the only instrument of the kind which steel rule. With care it was possible to read the Crosby is of real value, at any rate in the present state of knowdiagrams to an accuracy of half of i per cent. The optic ledge. For the army the rigid dirigible has certain disindicator diagrams could readily be measured to the same advantages. It is more difficult to work, to bring back, order of accuracy. The diagrams were plotted on squared and to bring to rest. It is more difficult for the army paper, and super posed one on the other, so as to exhibit than for the navy. The non-rigid dirigible is the best for whatever differences there were between the indicators.
army purposes. The aëroplane may become available for Speaking generally, the compression curves are coincident. army purposes, but at present it has certain defects. It The maximum pressures practically agree in two of the will have to rise much higher_before it can be a safe tests; in a third, the Crosby indicator gave the higher instrument for reconnoitring. But M. Blériot's splendid initial pressure, and in the fourth the Hopkinson gave the feat in crossing the Channel and the successes achieved in higher. Down the expansion line the two indicators agree the United States point to a time when the aëroplane for the third of the stroke. After that the Hopkinson indi- may be an instrument capable of achieving great results. cator gave a persistently higher expansion line, the difference To the navy has been assigned the duty of investigating, between the two lines being higher than the probable ex- with the view of constructing, the rigid dirigible, the ship perimental error of the measurements. The effect of this of the Count Zeppelin type. To the army has been difference is to make the Hopkinson indicator give about assigned the duty of experimenting with the non-rigid 3 per cent. higher mean pressure than the Crosby.
dirigible, the machine of varying type, and also with In the Hopkinson indicator the spring was in the form aëroplanes. of a flat bar rigidly fixed at the ends and loaded in the To make their study of aviation scientific, Mr. Haldane centre; the central deflection of this beam is a direct said the Prime Minister constituted the advisory commeasure of the pressure on the piston. During calibration mittee, under Lord Rayleigh's presidency, on which there with dead weights, from which the scale of the spring is is some of the best scientific brains in the world. Conobtained, the ends of the bar may be assumed to be tinuous work has been going on at the National Physical absolutely fixed, but when the indicator is in use it is Laboratory. Meetings have been held there and possible that there is a slight slip in the bar through the Aldershot and the War Office. The committee is to screws which restrain it. The effect of this would be to advise, its purpose is to scrutinise inventions submitted prevent the pressure falling so rapidly in this indicator in the course of the work of the departments concerned, as in the Crosby indicator. The author believes that this and to conduct systematic experiments. In a few days explanation is more likely to be correct than that the the first report of this committee will be made public. effect is due to inertia or friction, and is inclined to prefer The committee, said Mr. Haldane, has such men as Lord the results obtained from the Crosby indicator.
Rayleigh and Dr. Glazebrook on it, and such men While the results of this comparison do not offer the practical side as Mr. Lanchester and Mr. Mallock, absolute proof of the accuracy of either indicator, there and others like Prof. Petavel and Dr. Shaw, and also is still strong evidence that both give results very close such high authorities on the army and navy side as to the truth. The indicators are of entirely different types, Major-General Hadden and Rear-Adiniral Bacon, and is one multiplying the indicator piston movement by six, well furnished from the various points of view. This the other by about 120, a very similar multiplication committee has been at work, and the first thing it has being the case with the rotation of the drum and the done is to determine the general question which should mirror. In the optic mirror inertia is certainly negligible. be studied. There have been various memoranda by the That the two give results to within 3 per cent. on the experts on stability, screw propellers, wind structures, mean pressure, and very nearly the same figures for the petrol motors, and a very difficult thing which has arisen initial pressure, is good presumptive evidence that, when in connection with balloons, the accumulation of electroeither indicator is used with the precautions regarding static charges. Everyone knows what a peril electricity is driving described, the results so obtained are at least as in the air. Then the committee has mapped out the accurate as any other measurement which can be made general field of its work. There are certain general quesin engine testing. Unless these precautions are taken, the tions in aërodynamics, questions specially relating to aēroresults can only be regarded as affording a clue to the planes, such the mathematical investigations of valve setting, and give no trustworthy figures as to the stability, the effect of rudder action, gusts of wind, and power developed in the engine cylinder.
half a dozen other things which I need not enumerate. The council of the institution has issued the conditions There are propeller experiments; there are questions reunder which the second award of the water arbitration lating to these motors which have to be of special conprize will be made in 1910. The prize will have a value struction for air work, general questions relating to airof about 301., and will be awarded to the author of the ships, and still more general questions relating to best original paper dealing with any branch of the meteorology. mechanics of the supply or distribution of water. The The committee has entered into communication with the latest date for sending in papers will be September 1, Aëronautical Society, the Aërial Club, and the Aëro
League. The design is to afford assistance to private
inventors wherever this can properly be done, because MR. HALDANE ON THE PROMISE OF
progress in this matter will be, not merely a Government,
but a national matter. The Admiralty is concentrating, AVIATION
under Admiral Bacon, Director of Naval Ordnance, on IN Committee on the vote of 36,4641., including a sup
the building of a rigid dirigible of the very largest type, plementary sum of 6500l., to complete the sum at least the size of the Zeppelin. That is being built at necessary to defray the charge for sundry grants in aid, Barrow-in-Furness by Messrs. Vickers. The combination scientific investigation, and other grants, there was of experts and practical men may give us a practical interesting discussion in the House of Commons on result some time next spring.
The War Office is reAugust 2 on the subject of aviation for naval and military organising its factory at Aldershot. The instruction, which purposes. Mr. Haldane made a statement giving the is at present given to balloonists under the superintendviews and intentions of the Government.
ence of Colonel Capper, is being separated from construc
tion, and at present preparations are being made for the the size and weight of the breech mechanism are reduced ; construction of a shed which will take in the largest on the other hand, the higher the proportion of nitrosize of dirigible. The Idmiralty has in prospect one great glycerine the higher is the temperature of combustion and rigid dirigible, the War Office has three, and besides those the greater the erosive effects on the surface of the bore we have our balloons for war purposes. At the present of the gun. time we have certain aëroplanes, and the prospect of two The presence of nitroglycerine in an explosive allows of new aëroplanes which are to be presented for experi- the more easy and rapid elimination of the solvent used mental purposes, and may hereafter be acquired. That in manufacture and of moisture, a small quantity of which is the actual position of things.
is always present in nitroglycerine and guncotton. The
sooner this is attained the better, because the longer the IMPROVEMENTS IN PRODUCTION AND
time that the powder is being heated in order to dry it, APPLICATION OF GUNCOTTON AND
the more likely is its chemical stability to be affected. NITROGLYCERINE.1
Moreover, it is a well-established fact that with nitrocellu
lose powders it is impossible to remove the volatile matter II.
with anything like the same completeness as can be done IN the year 1846 Schönbein discovered guncotton. In the in the case of nitroglycerine powders. The consequence
year 1886, that is, forty years later, the French chemist is that the slow evaporation from nitrocellulose powders Vieille invented his smokeless powder for military pur- of the residual volatile matter which takes place in store poses. This explosive, which was primarily designed for tends to produce changes in their physical character and use in the small calibre Lebel rifle, consisted essentially renders them in course of time liable to alter in ballistic of guncotton, and the secret of its success lay in the fact properties, and even to develop dangerous pressures in that Vieille so altered its physical state that its rate of combustion, when confined, was under complete control. Nitroglycerine powders are cheaper than nitrocellulose This condition was arrived at by treating the fibrous gun- powders, weight for weight, and even more so for equal cotton with suitable solvents which entirely destroyed the ballistic effects. fibre and converted it into a colloidal, horny substance The original cordite, the manufacture of which comquite devoid of all porosity. The gelatinised guncotton menced in 1890, contained a high proportion of nitroresulting from this treatment burnt, when ignited, from glycerine, 58 per cent., and the erosion produced, especially the surface inwards, and by varying the surface area any in large guns, was considerable. This led to experiments required rate of combustion could be obtained. The use being carried out at Waltham Abbey with the view of of smokeless powders manufactured in this way was very the production of a less erosive explosive, and the final soon extended to all natures of ordnance.
result was the introduction into the service, in 1901, of The next step in the development of smokeless powders a modified cordite known as cordite M.D.," in which was the combination of nitroglycerine with nitrocellulose. the percentage of nitroglycerine is reduced to 30 per cent., The first powder of this type was the “ ballistite” of so that the composition becomes :-nitroglycerine, 30 per Alfred Nobel, patented by him in the year 1888. The
cent. ; guncotton, 65 per cent. ; and mineral jelly, 5 per original ballistite was composed of equal parts of nitroglycerine and of soluble nitrocellulose, a variety of gun- The constants of explosion of cordite and cordite M.D., cotton soluble in nitroglycerine, and no solvent was there- determined at the Royal Gunpowder Factory some little fore required in its preparation, although a certain pro- time ago, are as follows :portion of camphor was used to promote the solution of the nitrocellulose. Another form of nitroglycerine-nitrocellulose explosive is the British service powder, cordite,
Gaseous which originally consisted of nitroglycerine, 58 parts, gun
Loading Volume, Water
at oC.. cotton, insoluble in nitroglycerine, 37 parts, and mineral
760 mm. jelly, a product of the distillation of crude petroleum, 5 parts. To effect the gelatinisation of the guncotton, the
Calories per solvent acetone, obtained indirectly from the destructive
C. distillation of wood, is employed. The result of subject
2663 ing nitrocellulose in suitable machines to the action of
2374 nitroglycerine or of solvents, of which there are several suitable ones besides acetone, is to destroy its fibre and An inspection of these figures shows that the alteration convert it into a gelatinous mass, in which condition it in proportions of the explosive ingredients results in a can be formed into any desired shape. Where solvents decrease in the heat of explosion of about 16 per cent., are used to produce this result they remain in the mass and an increase in the volume of gases of about 51 per during subscquent operations, and are finally driven off cent., whilst there is a decrease of 289° C. in the temperaby means of heat. The resulting products, somewhat in- ture of explosion. correctly termed " powders,” which are manufactured in As would therefore be expected, the erosion produced by a variety of forms, such as grains and flakes of different cordite M.D. is very much less than that produced by the shapes, ribbons or strips, solid cords, tubes, &c., vary in original cordite for the same ballistics, and is certainly consistence with the quantity of nitroglycerine they con- not greater, if as great, as that produced by the best tain. The more nitroglycerine present the softer the forms of nitrocellulose explosives. powder, pure nitrocellulose powders being hard to brittle- Although of minor importance to smokelessness, flame.
lessness is a desirable quality for propulsive explosives to For practical purposes modern smokeless powders are possess. In this respect cordite M.D. is superior to cordite of two types :
in the case of rifies and machine guns; unfortunately, a (1) Those consisting entirely of nitrocellulose,
suitable ingredient has not yet been discovered which will termed“ nitrocellulose powders.
render smokeless powders flameless in large guns. (2) Those consisting of a mixture of nitrocellulose and A third ingredient in both natures of cordite, viz. mineral nitroglycerine, known as nitroglycerine powders.' jelly, although present in a comparatively small propor
Opinions differ somewhat as to the relative merits of tion, is a very important constituent. these two types; in this country the latter type is pre- Cordite in the advanced experimental stage consisted of ferred. Their characteristic features are, briefly, nitroglycerine and guncotton alone, and as their combus. follows:
tion produced no solid residue of any kind, the surface of A nitroglycerine powder is more powerful than a nitro- the bore of the magazine rifle in which the early expericellulose powder, and the more nitroglycerine present the ments took place was not fouled in any way. The result more powerful the explosive. Therefore, for equal was that the cupro-nickel coated bullets, propelled in ballistics, a smaller charge of the former than of the latter succession at high velocity through a clean barrel, de. is required, and, consequently, the chamber capacity and posited some of the cupro-nickel in the bore. In order 1 Discourse delivered at the Royal Institution on Friday, January 29, by
to prevent this a number of substances were incorporated Sir Frederic L. Nathan, R.A. Continued from p. 147,
with the nitroglycerine and guncotton, with the object
Heat of Explo. Total Gases, i
c.c. per gram.
of producing a deposit in the bore, which it was hoped must be a heating test, and it must be possible to correlate would get rid of the difficulty of metallic fouling. Of the temperature and duration of the test with any given all these various substances the one which appeared to temperature and duration of storage. The rate of deterioraanswer the purpose most satisfactorily was refined vaseline, tion as a function of the temperature was determined by and this material became the third ingredient of cordite Dr. Will for guncotton, and later by Dr. Robertson at as eventually introduced into the British service. When Waltham Abbey for nitroglycerine. From these and other the manufacture was commenced on a large scale, vase- experiments carried out at Waltham Abbey, a factor of line, which is the proprietary name of one of the refined increase in rate of deterioration of cordite with increase products of the distillation of petroleum, was replaced by of temperature was deduced. This factor having been mineral jelly, the same material, but in a cruder form. determined, what is known as the “ silvered vessel test
The original object with which mineral jelly was intro- was worked out at the Royal Gunpowder Factory. In duced was of no importance when cordite was substituted this test, of which the details will be described presently, for the black and brown powders used in large guns, but cordite is heated in a specially designed vessel at 80° C., in order to have but one nature of smokeless powder in a temperature not too far removed from those to be met the service mineral jelly was added to all cordite, whether with when cordite is stored under the worst service confor use in small arms or artillery. Subsequent experienceditions, and the number of hours' heating at this temperahas demonstrated how very fortunate was the selection of
ture any given sample will stand before it shows signs this material for rifle cordite and the extension of its of active decomposition are ascertained. Then, by means use to all sizes of cordite.
of an equation, containing the factor connecting rate of Mineral jelly is one of the best ingredients it is possible | increase deterioration with rise in temperature, a calcuto have in smokeless powders from the point of view of lation can be made converting the hours of heating at their chemical stability. This important fact, not recog- 80° C. the sample withstood to years and fractions of a nised originally, was brought out in the following way. year it would stand at any given temperature of storage, In order to facilitate the explosion of cordite in blank and therefore a knowledge is obtained of how much longer ammunition for the rifle it was cut into very thin Aakes, it would be safe to store this cordite at any given temperaand the non-explosive mineral jelly was omitted from its ture. composition. After a comparatively short storage in a This test was applied to a considerable number of hot climate the stability of the smokeless blank, as it samples of known age and thermal history. From these was called, was found to have suffered seriously, whereas data, and knowing the number of hours at 80°C, that the stability of normal cordite containing mineral jelly newly made cordite of good stability will stand before was not appreciably affected. These facts led to
showing signs of decomposition, the number of hours that thorough investigation at Waltham Abbey of the action the different samples should stand the test were calculated. of mineral jelly in preserving the stability of cordite, and When the samples were actually tested, the number of it was discovered that mineral jelly contained constituents hours' heating at 80° C. they withstood were in close which had the valuable property of combining with the agreement with the number of hours it was calculated decomposition products (the result of prolonged storage they should stand. of cordite at high temperatures) to form stable bodies, The form of vessel in which the heating is carried out thus removing these decomposition products, which un- is the well-known vacuum vessel of Sir James Dewar. doubtedly exert a deteriorating influence on the cordite A glass bulb silvered externally is enclosed in an outer from their sphere of action.
bulb silvered internally. The space between the two is When Abel was engaged on his researches in connection highly evacuated for the purpose of limiting the dissipawith the production and properties of guncotton, it was tion of any heat evolved by exothermic changes on the obvious to him that some test of a chemical nature was one hand, and on the other for the purpose of minimising required in order to ascertain whether or not the finished the effect of accidental slight changes in temperature of guncotton had been thoroughly purified in manufacture. environment. It will be remembered that accidents occurred in the early In the centre of the inner bulb is situated the bulb of days of its production because this purification had not a thermometer, the stem of which passes through a cork been carried sufficiently far. The test which he devised in the neck of the vessel. A side tube is attached for the was based on the principle that if guncotton be subjected purpose of making observations on the colour of the gases to an elevated temperature, traces of oxides of nitrogen evolved. For heating the vessel a bath is provided with will be given off, and will reveal their presence by acting cylinders closed at the bottom, and wide enough to admit on a suitable reagent.
the vessel to such a depth as the side tube will permit. The test is carried out by heating guncotton in a test. The bath is surrounded by insulating materials.
The tube placed in a water bath, and suspending over it a vessels are packed in the cylinders with wool yarn, and strip of moistened filter paper impregnated with potassium the tops of the cylinders are closed with felt discs to iodide and starch. If the purification of the guncotton exclude draughts. has not been sufficient, the discoloration of the test paper The bath is fitted with a gas regulator or other means takes place early; as the result of experience Abel fixed for securing that the temperature of the explosive is kept a time before which no reaction should take place. This constant. test, known as the Abel heat test, is a test for the purity The cordite is coarsely ground, and 50 grams are used. of guncotton and of nitroglycerine, and of freshly made Readings of the thermometer are taken at intervals, explosives containing either one or both of these in- and the time is noted when a rise of 2° C. in the temperagredients. For this purpose no test has yet been devised ture of the explosive above the temperature of 80° C. which equals it. But it was never intended to be, and
At the same time, visual observations are made is not, a quantitative test, and is therefore only a rough as to the colour of the column of gas in the side tube, guide, though a very useful one, as to the stability of since it is found that, previous to the rise in temperature an explosive which has been in store for more or less occurring, orange-coloured fumes of nitric peroxide are prolonged periods, or under more or less adverse con- evolved. When the temperature exceeds 82° C. the test ditions.
is complete, and the flask is withdrawn. The number Smokeless powders of the types dealt with are all sub- of hours which have elapsed since the start of the test ject to deterioration, and there is very little doubt that is the measure of the stability of the cordite. this deterioration is for any given explosive a function Until about sixty years ago, the only explosive known of the temperature of storage. The higher the tempera- for all purposes was gunpowder. With the discovery of ture the more rapid the deterioration.
guncotton and nitroglycerine, gunpowder was gradually The necessity, therefore, of some quantitative test which replaced by them for blasting purposes. In their early would enable a judgment to be formed as to the extent days the two explosives were used singly, guncotton as of deterioration suffered by any given sample of cordite guncotton, nitroglycerine-first of all alone-and then as is obviously of great importance, because such a test | dynamite. Later on the two were combined as blasting would afford the means of determining how much longer gelatine and explosives of a similar nature, but it was it would be safe to store any given batch of cartridges quite forty years after their discovery before cither became or lot of cordite at any given temperature. Any such test of practical use for propulsive purposes.