SCIENTIFIC!.

Otago Witness, Issue 953, 25 April 1889, Page 35

SCIENTIFIC!.

The Mechanical Feature of a Dust Explosion. ,

A few years ago, says- the. Monitor, such a story as recently came from Ohioago regarding the explosion at the oatmeal factory would have been received with general incredulity. That a force, comparable in its efforts with dynamite, could have been developed through the burning of the dust so familiar in the atmosphere of flour mills, would not have been believed. Subsequent investigation seems to show that dynamite was at the bottom of that mischief, but this will not affect the argument. , The subsequent destruction of ,& candy factory and of one of the great flouring mills at Minneapolis, as 'well as numerous lesser accidents, "have familiarised the public mind with the possibility of auch catastrophes. But there are some who are still unable or unwilling to be conyinced, that flour dust may be as fatal as gunpowder. The difficulty is this : If fire comes in contact with powder, dynamite, ( , or any other ordinary explosive, the .result is. certain and instantaneous. An atmosphere of dust, on the contrary, be ita. contact with a flame.., Th'^iyH^pMi^y. apP aren t ; change in its charaotery-it/fihould s suddenly explode after so long 'B.enSl6Mtratiiii^ its harmless qualities, se^nis/inc'rissdi.bleVi, The, enigma jwould be -iless perplexing if the mechanical' properties .■ of- matter were more generally understood.. The ; latest adyances in scientific investigation prove more and more conclusively that mechanical modifications are at the bojttonr of all the varied forms and properties ,o,f matter; that we are, in fact, " dealing "with a substance whose essenß^ is *tne , same', whether ,it be gold .ot iron 1 or earth or.^vatety or any other material with which we are acquainted— that ,it is the building ( up of the atoms, their mechanical structure! 'which determines- to which of the great classes of metals or minerals: the substance shall belong. The same atoms may be gunpowder, or ; they may be clay; they may be water, or air, or lead, according to their mechanical arrangement. Chemistry in its last analysis would seem' to be nothing more than the laws and principles of the mechanical arrangement of atomic quantities. . ■ '

.When this truth is ■ recognised it is easier to understand how a dust-laden atmosphere may suddenly develop"' the most dangerous -properties after years of apparent harmlessness. That dust will burn in the presence *of flame and air, and that the product will •be a gas much greater in volume, all will admit who have ever tossed a handful of f flour dust on the fire. But the conditions j under which a dust-laden atmosphere will I burn are so peculiar' that;, experimentally, Hhey rarely- occur. t . Every boy who has •kindled a bonfire.' knows how much his"success will depend upon the arrangement of |sthe sticks and the strength of the fire already Until sufficient volume of flame is secured each stick must be carefully adjusted \to support the slow combustion of its fellows. ;But once under full beadway,,hje may toss his sticks as he pleases, and they are instantly licked in the embrace of the roaring ffire. j Somewhat after the same fashion we may jregard the flour dust. Until the distribution jof particles has reached a point where they jwill sustain each other in creating a volume of flame, no explosion will occur. The in- [ dividual in contact -with-a lamp; or .candle may be insensibly consumed, while their fellows float harmlessly around them. But once the precise conditions are present, the flame", with ever-increasing energy, shoots through the mass and the explosion follows. Fortunately, the conditions favourable to such a disaster axe so rare that scepticism stall prevails.

MISCELLANEOUS,

— Sound is the sensation produced on us -when the vibrations of the air strike on the drum of our ear. When they are few the sound is deep ; as they increase in number it becomes shriller and shriller; but (says a writer in the "Popular Science Monthly") when they reach 40,000 in a second they cease

'to be audible. Light is the effebtproduced on us when waves ojE. jpghtrftrike on the eye. When four hundred millions of millions of vibrations of ether strike the retina in a second, they produce red; and as thenumber increases the.colour passes into orange, then yellow, then green, blue, and' violet. But between 40i000 vibrations in a second and four hundred millions of millions we have'no sense capable of receiving the impression. Yet between these limits any number of sensations may exist.' We have five senses, and sometimes fancy that no others are possible. ' Bufr it is obvious that we cannot measure the infinite by our narrow limitations. Moreover, looking at the question from the other side, we find in animals complex organs of, sense, richly supplied with nerv.esj.but the function of , which we are as yet powerless to explain. There may be .50 other senses as different from ours as sound is from sight; and, even within the boundaries of our , own senses, there * may. be endless sounds which we cannot hear, and colours as different as red, from green of which we have no conception. The familiar •world which surrounds us maybe a totally different place to other animals. To them it may be full of music which we cannot hear, of colours which we cannot see, of sensations which we cannot conceive.

— Is the saltness of the sea uniform at all depths 1 It has been generally supposed that the saltness of the waters of the ocean increases steadily with their depths, but the laborious investigations of Mr Buchanan (the chemist ' and physicist who accompanied the Challenger expedition) show that as a rule the saltness diminishes from the surface to a depth of from 800 to 1000 fathoms, and from thence increases until the bottom is reached. The average quantity of saline matter in sea water is about 3 per centi,' but it varies in different parts of the world from I*2 per cent., or 261b of salt per ton of water, in the Black Sea, to 4-3 per cent.; or'96lb per ton, in the Eed Sea; At great depths the composition of the waters of all the oceans is nearly identical.

—Although there is a very great difference between wool 1 and hair, it is found quite difficult to correctly state what that difference is —the one sometimes seems to run almost imperceptibly into the other. A correspondent of the St.' Louis Globe-Democrat furnishes the following very interesting paragraph on this subject : — The difference between wool and hair is not so great as might be supposed, since very fine hair bears a strong resemblance to very coarse wool ; but when the microscope is brought into operation a marked difference may be observed. The surface of the air will appear to be perfectly smooth, as though it were polished, while the surface of a fibre of wool is imbricated, as though the trunk were covered with infinitely small | scales. A hair is therefore seen to be an entirely different thing from a fibre of wool ; and a further variation is noticed in the fact that hair never curls in the way wool does, for hair— when it is curly at all— curls in long wavy lines, and wool in short half circles, which almost return into themselves. The texture of wool is also varied by fine I lines from 2000 to 4000 in the inch ; so by means of the microscope, wool may be easily known from cotton or any other animal or i vegetable fibre.

The New Glass for Microscopes is , still attracting much attention, and seems ]to be producing remarkable results. This ; glass possesses so. high a refractive power as to be rid of w"hat is known' as the secondary spectrum in lenses, and therefore does : away, with that' Confusion' in 'the focus which formerly existed in the best lenses. Employing these new lenses, Dr Dallinger, an eminent English naturalist, states that he has been enabled to discover a remarkable fibres, and which acts as a sort of gleaner in the ■ organism, which is endowed with six motile putrefactive fluid, the object of the existence of these organisms, he says, in the putrefac- • tive fluid being to break up^h.e decomposing animal and vegetable matter into its original elements with carbon, hydrogen, nitrogen, * and the rest, in order that, set free, they may , go, again to the building up of organic forma. .This organism, it appears, lingers in what has hitherto been considered an exhaustive 5 liquid to break up the minute particles still ileft, and to this end is endowed with an extraordinary power o£ motidn; this being •partly grinding and partly impact with 'motion ; a group of these organisms can be ! observed. abqu,t a mhaute speck of decomposing matter, rapidly breaking it up, until it has wholly disappeared; Dr Dallinger also ;says that he has been able, by the same lenses, to make discoveries on the obscure ,but important question of the existence and meaning of the nucleus in the^se minute organisms, demonstrating, in fact, that every : important change taking place in the organism, from its earliest development to its 'latest phase; was preceded by profound changes in this exquisitely minute nucleus. Photographing Eifle Balls.— The interesting process of photographing rifle in motion, by means of the electric fright, presents some remarkable phenomena, .judging from the experiments made by |Mach, the Austrian chemist. In this operation his plan is to .illumine the bullet by 'letting it break an electric current formed, 'but the velocity of the bullet must exceed jthat of sound, in order that the conditions ,of the air before and behind the projectile can ibe shown. After various experiments he jsucceeded in h;s efforts to photograph projectiles fired by W^rn^ and guns, having respectively an initial velocity of 438 jand 530 metres ,per Second. The , photographs obtained in this manner showed an air formation in front .of the bullet, having $he form of a. hyperbola, while behind it almost a vacuum was formed, in which, iwhen the initial velooity was very great, there were some curious spiral motions. From the description given there appeared from these photographs to be a great similarity between the motion, of a body through the water and that of a projectile through the Mr.

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