THE CHEMICAL NEWS. tonated, a result which is obtained with greater certainty VOL. XXXIX. No. 1014. RECENT CONTRIBUTIONS TO THE HISTORY By Professor ABEL, C.B. F.R.S. THE physical character of explosive substances, as also the mechanical condition of a mass of the particular explosive substance operated on, are of great influence in determining its behaviour when submitted to the action of an initiative detonation. The liquid nitro-glycerin is far more sensitive to detonation than gun-cotton; one grain of mercuric fulminate, confined in a metal case, suffices to detonate nitro-glycerin when surrounded by it: but, in order to attain this result with any degree of certainty, it is necessary so to confine the nitro-glycerin as to prevent its yielding to the blow developed by the initiative detonation, and thus to some extent escaping from the operation of the sudden concussion to which the particles contiguous to the fulminate charge are submitted. If nitro-glycerin be mixed with solid substances in a fine state of division plastic mixtures may be obtained, and the liquid may thus be presented in something like a solid form to the detonating agent. If the particles of absorbent material be, moreover, of porous nature, as is the case with the infusorial earth called Kieselguhr, used in the production of dynamite, a solid nitro-glycerin preparation may be obtained which contains a very large proportion of the liquid (75 per cent by weight). In this condition nitro-glycerin may be detonated without any difficulty when freely exposed to air; and although it is diluted with a considerable proportion of absolutely inert material, its sensitiveness to detonation is not in the least diminished. Each particle of the diluent is enveloped in the liquid, so that no portion of the latter becomes isolated from the remainder by the admixture of inert solid matter; hence, when the initiative detonator is surrounded by such a mass it is in contact at all points with some portion of the nitroglycerin, and the latter is in continuous connection throughout, though no longer in a mobile condition; detonation is consequently as readily established and transmitted through the mass as though it consisted entirely of nitroglycerin. Indeed, while the liquid in its undiluted state, if freely exposed to air in a long layer, transmits detonation with difficulty and very slowly as compared with compressed gun-cotton (the observed rate of progression being, in several experiments, below 6000 feet per second), detonation is transmitted with ease and certainty through very long trains of a solid preparation of nitro-glycerin, such as dynamite, and the rate of transmission is decidedly more rapid than it is with compressed gun-cotton, a result which is in harmony with the greater sensitiveness to detonation and the greater violence of action of nitroglycerin. It has already been stated that gun-cotton may be detonated if a confined charge of not less than 2 grains of mercuric fulminate be detonated when closely surrounded by the substance. But in order to attain this result, the cellulose product must be presented to the detonating agent in a mechanical condition favourable to its action. Gun-cotton in a loose flocculent condition, or even if in the more compact form of a spun yarn or thread, cannot be detonated through the agency of a large fulminate | buried in the material. The light and loose gun-cotton is simply scattered with violence; portions are sometimes Abstract of a Paper read before the Royal Institution of Great Britain, Friday, March 21, 1879. inflamed by the heat developed where the fulminate is dethe less violent the detonation produced by the fulminate charge. If, however, the gun-cotton be converted into a compact form, either by ramming the wool or thread very tightly into a case, or better still, by reducing the guncotton fibre to a very fine state of division, and compressing it, when in that condition, into compact masses, it becomes susceptible of detonation by the initiative action of mercuric fulminate, and the quantity of the latter required to bring about detonation is small (down to the limit which has been named above) in proportion as the compactness or density of the compressed material is increased. Detonation, when established in compressed gun-cotton, is transmitted with great velocity throughout the mass, as already stated, or from one to another of contiguous masses, laid out in long rows, and even, though at a reduced rate, if small spaces exist between the individual freely exposed to air be detonated when in immediate conmasses. But, if a small mass of compressed gun-cotton tact with gun-cotton wool or loosely twisted yarn, the detonation will not be transmitted to these, but they will merely be scattered and perhaps inflamed. The difference in the behaviour of nitro-glycerin and of gun-cotton when presented to the action of a so-called initiative detonation under the different conditions spoken of above, admits of ready explanation. It was established, in the first instance, that the action of an initiative detonation is not ascribable to the heat developed within the detonating material itself in undergoing chemical metamorphosis. If it were so, the detonating mixture known as percussion-cap composition and other explosive mixtures, the detonation of which is attended by much greater development of heat than is obtained by the action of pure mercuric fulminate, should detonate gun-cotton more readily than the latter does, whereas very much larger quantities of such materials are required to attain that result. Moreover, the readiness with which gun-cotton is detonated should be solely proportionate to the amount of fulminate used, which has been shown not to be the case; and gun-cotton should be more readily detonated when in the loose and open condition than in the highly compressed or compact form, because the latter presents it in the condition least favourable, and the former in that most favourable, to ready and rapid transformation by heat. Again, the actual temperature required for the explosion of nitro-glycerin is very considerably above the exploding temperature of gunCutton, yet a very much smaller charge is required for the detonation of nitro-glycerin than is needed for the detonation of gun-cotton. On the other hand, a quantity of confined percussion-cap composition which, if it were pure mercuric fulminate, would be altogether inadequate for the detonation of gun-cotton, suffices for the detonation of nitro-glycerin. The action of an initiative detonation has already been compared to that of a blow from a hammer or falling weight. The readiness and certainty with which gunpowder, gun-cotton, and other explosive agents are detonated by the latter agency are regulated by several circum. stances; they are in direct proportion to the weight of the falling body, to the height of its fall, and to the force with which it is impelled downwards; to the velocity of its motion; to the mass and rigidity or hardness of the support upon which the substance to be detonated rests; lastly, to the quantity and mechanical condition of the explosive agent struck, and to its sensitiveness. Gunpowder is much more readily detonated by a sharp blow from a small hammer than by the simple fall of a heavy hammer, or by a comparatively weak blow from the latter. It is very difficult by repeated blows, applied at very brief intervals, to detonate gun-cotton if placed upon a support of wood or lead, both of which materials yield to a blow, the force applied by that blow being transferred through the explosive agent and absorbed in work done upon the material composing the support. But if the latter 188 End-on Illumination in Private Spectroscopy. be of iron, which does not yield permanently to the blow of the hammer, the detonation of those substances is easily accomplished. If the quantity of the explosive agent employed be so considerable as to form a thick layer between CHEMICAL NEWS. END-ON ILLUMINATION IN PRIVATE AND ITS AND ELECTRIC ILLUMINED By PIAZZI SMYTH, Astronomer Royal for Scotland, and Past President of R.S.S. Arts. (Continued from p. 168). PART III. the hammer and support, the force applied is to so great APPLICATIONS TO BOTH BLOWPIPE FLAMES an extent expended in imparting motion to the particles of the compressible mass, that there remains little or none by which its detonation can be accomplished, and if the material be in a loose or porous condition (as in the case of a powder or a loose wool), much work has to be accomplished in moving particles of the mass through a comparatively considerable space, in the operation of compressing them, so that a second or even a third blow is required for their detonation; whereas if, by blows or pressure previously applied, the explosive material will be presented in the form of a compact mass, the particles of which have little tendency to motion when force is applied to them, detonation will be much more readily developed. It appears, therefore, that the detonation of an explosive substance by means of a blow is the result of the development of heat sufficient to bring about most energetic chemical action, or change, by expenditure of force in the compression of the material, or by establishing violent friction between its particles, consequent upon the motion momentarily imparted to them, and that it is brought about with readiness proportionate to the resistance which they oppose to their motion by the degree of their contiguity to each other. The exceedingly violent motion of particles resulting from the sudden or extremely rapid transformation of a solid or liquid explosive body into highly heated gas or vapour (which is the effect of a detonation), must obviously exert force which operates upon a body opposed to it in a manner precisely similar to the force applied by opposing a body in the path of a solid mass which is set into very rapid motion. In other words, a detonation exerts a mechanical effect upon resisting bodies precisely similar to that of a blow from a hammer or from a projectile propelled from a gun. Just as the force of a sufficiently sudden or powerful blow from a hammer is transformed into heat by the resistance to the motion of the hammer which the particles of an opposing body offer, and by the consequent friction established between them, so the force or concussive action exerted by the matter set in motion when a solid or liquid is converted into gas or vapour, will also be transformed into heat, the develop. ment of which in an opposing body will be proportionate to the resistance to motion which its particles offer, and to the suddenness and violence of the concussion to which it is subjected. The power of accomplishing the detonation of nitro-glycerine, gun-cotton, or other highly explosive substances, freely exposed to the air, through the agency of detonation produced in their vicinity or in close contact with them, appears therefore corectly ascribable to the heat suddenly developed in some portion of the mass by the mechanical effect, or blow exerted by that detonation, and is regulated by the violence and suddenness (either singly or combined) of the detonation, by the extent to which the particles composing the mass of the explosive material are in a condition to oppose resistance to the force, and by the degree of sensitiveness of the substance to detonation, or to sudden metamorphosis, under the influence of heat thus developed. (To be continued.) Eupitton and Pittakall.-A. Grätzell.-The author points out a number of characteristics which distinguish eupitton from pittakall. The latter gives a blue precipitate with alkalies even in an acid solution, whilst eupitton forms a brown precipitate. Pittakall is precipitated from its acetic solution by acid acetate of alumina, whilst eupitton is not. It does not seem probable that Reichenbach was acquainted with eupitton.-Berichte der Deutsch. Chem. Gesell. Electric-Spark Spectroscopy in Vacuum Tubes. THE next step in spectroscopy, after flame lines, can hardly be anything else than the simple induction spark of electricity in rarefied gas tubes. For the most infinitely small weight of the particles to be moved or heated there, allows a very trifling quantity of electricity, and in uncondensed form, to produce abundantly visible effects. These effects, moreover, supplement in a remarkable manner our knowledge of gases as given by flame experiments. Thus on burning pure hydrogen flamewise in the open air, no spectral effects of lines or bands are seen; because, as it is said, the very act of burning being a combination of that hydrogen with the oxygen of the air, water is formed, and hydrogen ceases to exist as an independent entity. But in a close glass tube filled with hydrogen, the electric spark passing through it, heats that gas by itself alone; and then, not only do we see the hydrogen's spectral lines, but recognise them immediately as some of the most extensively distributed and most important throughout all the universe. For when the populace is in ecstasies at a total solar eclipse, on seeing the redprominences outside the sun's circumference, and wonders what they are,-the spectroscope pronounces them to be "flames of incandescent hydrogen of most enormous size." Again, when the astronomer finds occasionally what is called a new star, or rather an old one which has suddenly become 500 times brighter than before, and must be a sun on fire,-a sun destroying all the life on the planets immediately around it,—it is an immense extravasation of incandescent hydrogen which has done the business. And then we are induced to speculate on whether the similar in kind, though happily smaller in quantity, extravasations, which make the red-prominence round our own sun sometimes large and sometimes small, are, or may be, regulated by cyclical law; and what length of time, if any, may probably separate us from the next of their greater effluxes? These spectral lines of incandescent hydrogen (four in number, red, glaucous, violet, and a very faint one in the lavender) are therefore rather eerie things to look at; should never be forgotten by man; and may, in the meanwhile, be turned into, and have been already extensively used as, most useful companions at the spectroscope, through means of the following five inventions, none of them very old. Ist. Prof. Geissler of Bonn introduced the exceeding rarefaction of gases within hermetically sealed glass tubes, armed at each end with platinum wire electrodes. 2nd. Prof. Plucker, also of Bonn, brightened up the light of those tubes by reducing the diameter of the bore of the central part until it was no more than capillary. 3rd. M. Ruhmkorff of Paris improved and vastly reinforced the induction coil. 4th. Dr. Leeson planned the bichromate galvanic battery, with its notable power, and absence of poisonous fumes; and 5th. Some artist in arrangement produced the longnecked bottle-form of that battery, enabling its power to be called forth at intervals of either minutes, or months, or years, without any intermediate preparation or attention. For mere reference to the first three, and brightest ties. In fact I had stumbled, and at the very right time for it on one of the grandest cases of dispute in modern spectroscopy, viz., "Is it carbon vapour, or carbon-compound vapour? carbon by itself, or carbo-hydrogen ?" So I im. mediately increased the prism power 33° between A and H; and then, looking at the minute spectral space, which formed the crucial instance to be measured,-where, just in front of the "green giant," the best leading authority in the "Philosophical Transactions of the Royal Society," London, has only eight lines, and those dark ones,-I there saw most clearly, and measured, 31 lines, and all of them bright ones. hydrogen lines, a one-pint bichromate bottle, with a zinc | to air in any way, were caused by carbonaceous impuriplate 30 by 1'5 inches, a small coil giving a 4-inch spark, and a transverse view are enough, and even more than enough. But for original investigations into the more untoward of the gases for lighting up, far more power and illumination are necessary. To a certain extent, any wealthy observer can obtain that higher degree of illumination most easily, by merely increasing the size of his batteries and coils with the consequent length of their sparks. But then their at-the-same-time growing heat will crack and destroy the tubes so rapidly, that even the richest man may be at last driven to inquire, whether the end-on principle just brought forward, with the claim of increasing brightness without altering the temperature at all, be not applicable? It is a case for it undoubtedly; for the line of light in a Geissler-Plucker tube is still longer in proportion to its breadth than any blowpipe flame, and usually wastes its precious light in the proportion of 99 to 1. But as these tubes are now made they cannot be employed end-on. Their poles come in the way, two lions at once, totally obscure the view. A very considerable alteration of arrangement is therefore necessary; and not every manufacturer will take the trouble of experimenting for a single private observer. I wrote therefore to my trusty old friend M. Salleron in Paris; and he, with the enthusiasm of a scientist, joined to the practical capacities of a maker of instruments of precision, promptly realised for me one design after another of the end-on gas vacuum tubes, until we at length reached a very promising standard both of size and shape, as thus: The new tubes are shorter, broader, stronger than the old ones; more easy manipulated, and safely packed and carried; while, finally, in place of a uselessly long line of faint light, they give a small point of brilliant light. And they are likely to show this for a longer time; as, instead of that point of light (really the axis of the long capillary seen end-on) being looked at through the thick glass walls of the said capillary, which frequently get dimmed inside by oxidising and carbonising effect of the electric heat, they are viewed through the thin walls of the bulbs, whose very large diameter keeps down the heat on themselves and prevents those darkening effects. At the same time all the rest of the glass, except one peep; hole, being silvered externally (and then black-varnished for protection), there is some further increase of brightness by internal reflection. I show now a box of these tubes whose light, under a standard spark of 1 inch long, may readily be pronounced by eye-view alone, extremely dull if seen transversely; but remarkably bright, pungent, and star-like, if looked at end-on. The true test is, however, the result of actual spectroscopic observation. Viewed transversely, to the line of electric light, the spectrum of "air," simple atmospheric air, with a prism of 3° dispersion, begins inside the scarlet hydrogen line; and from thence to the lavender-grey, or other end of the spectrum, contains only 72 measurable features, and they of hazy, indistinct, unsatisfactory bands. But viewed end. on, the spectrum of the very same air tube, with the same spark and same prism, begins 18 lines or markings outside the scarlet hydrogen; and in the whole spectrum shows 221 measurable items, many of them being vividly sharp lines. Next, on increasing the prism power to a dispersion of 22° between A and H, but everything else remaining the same, the spectral lines were found so multiplied that 400 were quickly measured in a space where our first attempt had only 38. But I do not claim that all those 400 are truly air spectral lines; only that they were lines distinctly seen in a well lighted tube, said to contain chemically the purest possible "air-vacuum." And in fact I stopped where I did, in the green, instead of going on to measure about 1000 more lines that were waiting in the blue and violet, because it presently appeared most indubitably, that some of the lines just entered, instead of belonging After such an example as that, I need not probably say anything more in furtherance of the principle of the endon-view kind of gas vacuum tubes. But I would beg leave to call the attention of so practical a meeting as the present, to the facility of manipulating the end-on_tubes by means of the peculiar holder for them when under the electric spark; also to the anti-heating character of the large, thin copper plates adopted as terminals for the induction wires, in place of the small brass wire spirals, usually employed; and to the packing-boxes lined with cork and armed with thick grooved cork; all of which have been made for me, and greatly to my satisfaction by, Mr. John Air, of the firm of Air and Candow, cabinetmakers, Leith Walk. But the vacuum tubes themselves, including, besides the "air-pure," examples of— Nitrogen Nitrous Oxide Carbonic Oxide Marsh Gas Olefiant Gas, and Indeed I do have all been prepared, as already intimated by M. Jules Coal-Tar Colours.-Mr. W. H. Perkin, F.R.S., the discoverer of mauve, the first colour produced from coaltar, is about to read two papers before the Society of Arts on the 8th and 15th of May, in which he will give a full history of these colours, their chemistry and their technical applications. Experiments were made first of all as to the best area of a circular bore for the capillary; and proved that there is a lower limit which should not be passed if the full, as well as most intense, iilumination derivable from any given electric current is to be preserved; and at the same time, there is an upper limit of area where the light, though abundant, becomes too faint and diffuse. Further experiments were then made in flattening the most desirable areas of bore (as so often practised with thermometers), and adapting such flattened bore to the direction of the spectroscope's slit, in order to have a taller spectrum. But though the spectrum was thereby made taller, and its lines longer, the author found such bores (on the average of a dozen examples), more often clogged with opaque, ad. ventitious particles; and after a little practice, he did not find the greater length of lines necessary to accurate micrometer observation; while in proportion to such extra length, they waste the light whi h might otherwise be better employed. Whence he inclines, after all, to circular bores, as more easily manufactured, and more certainly tested as to whether they correspond, or not, to any proposed general standard of size. A standard of compound shape, as well as size, is far more difficult to have universally kept to. + For the ordinary tube-glass, so large an extra-dose of carbonate of soda, I am told, is usually introduced into the melting pot (to promote easy working at low heat and economise coal), that the glass becomes sally hygroscopic, and depositions of both water and carbonaceous matter form in the capillaries, and can never be com pletely cleaned out. 190 New Form of Wash-Bottle. EXTINGUISHING FIRES IN TAR DISTILLERIES, &c. By WATSON SMITH, F.C.S., F.I.C. Ir may not be known to all tar distillers that in cases of fire on their premises their best remedy usually lies close at hand, and this I will shortly endeavour to demonstrate from a basis of experience and fact. In the first place, however, it may be well to state that as a rule the tar distiller cannot get any fire insurance company to insure him, and it will therefore be seen that it is a matter of no light importance to be possessed of a ready and efficacious method of subduing the dread element, when it breaks out beyond its due bounds. This remedy lies in the crude ammonia-water, otherwise known as gas-liquor, which almost every distiller works up conjointly with the tar, and if in some cases this be not so, it would be little encumbrance, and well worth while, to obtain and keep a stock of, say, 1000 gallons of this gas-liquor. The way in which I first became aware of the eminent extinguishing powers of gas-liquors (now several years ago) is as follows:-A quantity of pitch was being run from a tar-still into the pitch-house, in which it is allowed to stand for some hours, to allow most of the noisome vapours to condense. By some means a flame came in contact with the vapours, an explosion occurred, and in a moment the roof was blown off, and the whole mass of molten pitch ablaze. Water, though thrown on it in quantity, seemed to avail nothing, and at last the supply accidentally ran short. Almost in despair, the pumps for raising the gasliquor into the ammonia-stills were adjusted so as to deliver a jet of the liquor upon the fiercely-burning pitch: the expedient acted like a charm, and the fire was quickly amothered. WCHEMICAL NEWS, May 2, 1879. the action is so powerful in a comparatively open space, and with such a refractory substance as burning pitch. It would seem, also, that the extinguishing power in the liquor would be even further called forth by a more intensely hot fire, for here, in all probability, the ammonia would be decomposed, and the generated nitrogen and hydrogen gases would help to swell the volume of non-supportive gas, displacing the air, and so choking out the combustion. I think there is considerable probability that at the high temperatures attained in some fires even the ammonia itself would be decomposed, with liberation of nitrogen and hydrogen gases, which in addition to the volumes of carbon dioxide and steam, choke out the flame by simple displacement of air. It might be said that if hydrogen and nitrogen be so liberated together, these, together with the H2S also set free, would do much to neutralise the effect of the non-combustible gases. Not so, however, for let there be but enough incombustible gas present, as there is, to displace the air, or to choke by excessive dilution the little which may remain or diffuse, then the combustible gases present, thus for the time prevented from burning, would assist in smothering the flame (being non-supporters of combustion) with as good a will, if one may use the expression, as the incombustible ones. I would strongly recommend every tar distiller, who also works up gas-liquor, to so arrange his pumping-gear that he may be able to throw jets of this liquor into any part of his yard or works where fire might break out and prove disastrous. If gas-liquor be not worked, then I would advise that a stock of, say, 1000 gallons be purchased. In a small works this might be advantageously stored in a tank or old boiler mounted on brickwork, at such an altitude as to give pressure enough to furnish a good jet for service below when required. Of course this reservoir should be covered to prevent evaporation. A NEW FORM OF WASH-BOTTLE. IN the CHEMICAL NEWS, vol. xxxix., p. 19, Mr. M. H. Foye gives a description of an ingenious form of washbottle, the special feature of which is the introduction of a short piece of india-rubber tube in the course of the mouth-tube. By compressing this between the cork and the finger communication is cut off between the mouth and the bottle. The advantages of this are (1) that after blowing into the bottle and then compressing the rubber tube, the pressure of air is sufficient to maintain the jet of liquid for some time; this jet can be instantly stopped Looking at the frequent occurrence of disastrous fires in cotton-mills, especially those of Lancashire, I wrote some years ago to an eminent local paper, strongly recommending that the owners of cotton-mills should set tanks on the tops of their mills, and furnish these with supplies of ammoniacal gas-liquor, to be always ready for service. I gave, too, a short description of the best way of arranging pipes to these different rooms. The gas-liquor itself, by careful manipulation, may be pumped off very fairly clear, and free from tarry matter. Of course, besides to fires in cotton-mills and tar-distilleries, this mode of fire-extinction might be all but universally applied. It may, indeed, be readily imagined how a jet of the liquor thrown into a burning room would act, the space being so enclosed, when NEWS instructions given by Mr. Foye, it struck me that, for use with hot or unpleasant liquids, some improvement would be effected by combining Mr. Foye's plan with that of another form of bottle, which is described in Prof. Thorpe's "Quantitative Analysis" (p. 55). The special feature of this latter form consists in the attachment to the bottom of the mouth-tube (a b) of a valve, constructed of a piece of rubber tube (bd), closed at the lower end by a bit of glass rod (c d), and provided with a slit (e), which remains closed except when the mouth-piece is blown into. The advantage of this form of bottle is that unpleasant gases are completely cut off from the mouth-piece (a). But there are the defects (1) that it cannot be used for hot water, because the only exit from the bottle being by the jet-piece (fhi), as soon as the water approaches the boiling-point the pressure of steam causes it to dribble or squirt out of the jet; and (2) that in the case of cold liquids, after the bottle has been blown into, the jet of liquid continues until the elastic force of the air inside has been expended; hence the jet is not fully under control. In Mr. Foye's bottle the jet is completely under control. In the case of hot water, however, the mouth-piece (a) is the exit for escaping steam, and hence, although this steam can be cut off before applying the lips, the mouth-piece has already been rendered more or less hot. With unpleasant gas, after the rubber tube is closed, the mouth-piece above the rubber tube still contains some of this gas, which is free to enter the mouth. Forgetfulness to remove the lips before releasing the rubber tube will allow gas or steam from the bottle itself also to enter the mouth. The modified form of bottle that I have adopted is represented in the accompanying sketch. The mouthpiece has the valve (b d) attached to the lower end. ƒgi is a jointed jet-piece of the ordinary form, the small glass tube (i h) being inserted into the large one (ƒh), with a bit of rubber tube (gh) between. jk is a third tube, penetrating the cork obliquely, and bent at k at an acute angle. A piece of rubber tube (1) is, at one end, slipped on to k and terminated at the other by a short bit of glass tube (m). Outside the rubber tube (1) is one of considerably larger diameter (n). If such a bottle be used for hot water, the steam escapes from m, and hence the mouth-piece (a) remains perfectly cool. On compressing the tube n with the forefinger and blowing into a, a jet issues from i, which continues after the removal of the lips until the elastic force of the air in the bottle is expended, but which can be instantly stopped by releasing n; the use of the outer tube (n) is as a non-conductor. The tube / becomes hot from the issue of steam, but n, being separated from it by an air space, remains sufficiently cool for the finger to be placed on it without discomfort. A bottle of this sort must, of course, have the neck wound round with twine or other material to keep the hand cool. If the bottle be used for cold liquid only n may be dispensed with. By shifting the valve (b d) from the mouth-tube to the tube j, the bottle may, if desired, be instantly converted into one on the ordinary plan, or if this be considered unnecessary, the bend of the tube at j (which must be made after the tube. has been inserted into the cork) may be dispensed with. For cold water Mr. Foye's bottle is preferable, as liquid can be poured out by the mouth-piece and the flow accurately regulated, which cannot be done with that I have described. Calcutta, March 27, 1879. The Government Patent Bill.-A paper on the "Government Patent Bill" will be read before the Society of Arts on Wednesday evening next, the 7th inst., by W. Lloyd Wise, A.I.C.E. F. J. Bramwell, F.R.S., in the Chair.-Ber. der Deutsch, Chem, Gesell, EXPLOSIONS IN FLOUR MILLS. By H. W. LANGBECK. IN the Annales de Chimie et de Physique there appeared, last year, a communication from L. Smith to Dumas concerning the explosive mixtures of finely-divided organic substances and air, especially of flour and air in some mills at Minnesota. Mr. Smith supposes that meal-dust diffused in the open air was inflamed through the heat produced by the friction of the millstones turning with great rapidity. I think I am justified in opposing that explanation and substituting another one. Years ago I visited a friend, proprietor of a steam-mill, and there I noticed that the grains crushed between the millstones produced a smell like that of impure hydrogen. I called my friend's attention to the danger that might arise from want of sufficient ventilation, but laughingly he replied that there was nothing to fear. I forgot the matter until the above-mentioned explosion reminded me of it. In order to convince myself of the correctness of Mr. Smith's supposition, I put some meal-dust, previously heated, in a dry bladder, blew air into it, and having diffused the dust by shaking, I directed the point of a gasflame by means of a blowpipe into the opening of the bladder (an electric spark would have been preferable, but was not at hand). No explosion took place. I allowed, then, coal-gas to enter the bladder, and repeating the experiment, a violent detonation was the expected consequence. Meal-dust diffused in a balloon, and blown through a gas-flame, was ignited; but this was, of course, not the condition on which the explosion at Minnesota took place. But what may be the source of the hydrogen, if indeed present? The amount of fat in wheat flour varies between 1 to 19 per cent, of bran 4 to 4'7 per cent, of maize, perfectly dried, 8 to 9 per cent. Is water predisposed to oxidise the fat through heat produced in grinding, thereby setting free hydrogen? Has the change of a small amount of starch into dextrin and glucose during the grinding process something to do with it? CONVERSAZIONE AT THE ROYAL SOCIETY. ON Wednesday evening last the President of the Royal Society, Mr. W. Spottiswoode, gave a Soirée at Burlington House, which was largely attended. The novelties exhibited in the various rooms attracted great interest. In the first room were exhibited Mr. Crookes's Exhausted Tubes and Apparatus illustrating various phenomena conThe nected with Molecular Physics in High Vacua. following is a description of the experiments which were shown: 1. Dark Space round the Negative Pole.-When the spark from an induction coil is passed through an ordinary vacuum tube, a dark space is seen round the negative pole. The shape and size of this dark space do not vary with the distance separating the poles; nor, only very slightly, with alteration of battery power, or with intensity of spark. This well-known dark space appears to be a layer of molecular disturbance identical with the invisible layer of molecular pressure or stress, the investigation of which has occupied the exhibitor some years. 2. The Electrical Radiometer.-An ordinary radiomete is furnished with aluminium cups for vanes. The fly is supported by a hard steel cup, and the needle point on which it works is connected with a platinum terminal sealed into the glass. At the top of the radiometer bulb a second terminal is sealed in; the radiometer can therefore be connected with an induction coil, the movable fly being made the negative pole. At low exhaustions a velvety violet halo forms over each side of the cup. On increasing the exhaustion the dark space widens out, retaining almost exactly the shape of the cup; the bright |