Science.

Poverty Bay Herald, Volume X, Issue 2026, 15 September 1883, Page 2 (Supplement)

Science.

Properties of Nitro-Glyccrinc.

It has a sweet, aromatic, pungent taste, and possesses the very peculiar property of causing an extremely violent headache when placed in a small quantity upon the tongue, or any other portion of the skin, particularly the wrist. It has long been employed by homoeopathic practicioners as a remedy in certain kinds of headaches. In those who work much with it, the tendency to headache is generally overcome, though not always. It freezes at about 40 degs. Fahr., becoming a white half-crystallized mass, which must be melted by the application of water at a temperature of 100 degs. Fahr. If perfectly pure — that is, if the washing has been so complete as to remove all traces of the acid — it can be kept for an indefinite period of time; and, while many oases of spontaneous combustien have occurred in impure specimens, there has never been known such an instance, where the proper care has been given to all the details of the manufacture. When pure, nitro-glycerine is not very sensitive to friction, or even to moderate percussion ; if a small quantity be placed on an anvil and struck with a hammer, that portion which is touched explodes sharply, but so quickly as to drive away the other particles ; if, however, it were even slightly confined, so that none could escape, it would all explode or detonate. It must be fired by a fuse containing fulminate of mercury (the compound used m percussion caps), not being either readily or certainly fired by gun-powder, the shock of the latter not being sufficiently quick or sharp to detonate the nitro-glycorine. It is highly probable that in this case, as in that of other high explosives, the vibrations set up by the fulminate (which is not stronger than gunpowder) are of just such a character to find an answering chord, so to speak, in the explosive, so that the desired effect is produced. This would seem to bo a correct theory, for it is not always the most powerful explosive which most readily causes the explosion of another body. For instance, although nitro-glycerine is much more powerful than fulminate of mercury, yet seventy grains of it will not explode gun-cotton, while fifteen grains of tbe weaker fulminate will readily do so. The fuse generally used, then, for firing nitro-glycerine, is composed of from fifteen to twenty-five grains of fulminate, and this quantity is sufficient to detonate a large mass as well as a small one. If flame be applied to nitro-glycerine it will not explode, but burn with comparative sluggishness. When frozen it is very difficult and uncertain of firing. If the material be perfectly pure it forms, upon detonation, a volume of gases nearly thirteen hundred times as great as that of the original liquid ; these gases are also further expanded, by the heat developed, to a theoretical (though not practical) volume ten thousand times as great as that of the charge. : : ; Practically speaking, the forces exerted by gunpowder and nitroglycerine are in the same proportion of one to eight. — From •' Explosions and Explosives" by Allen D. Broion, in Popular Science Monthly. Tuk amount of light given out by a gasflame depends upon the temperature to which the particles of solid carbon in the flame are raised, and Dr. Tyndall has shown that of the radiant energy set up in sjuch a flame, only the l-25th part is luminous ; the hot products of combustion carry off at least four times as much energy as is radiated, so that not more than one-hundredth part of the heat evolved in combustion is converted into light. At a recent meeting of the Academic des Sciences, M Boussingault showed the members an old bronze chisel found in Peru, of the Incarial period, remarking that he had never been able to produce the hardening to which the old bronze was supposed to be subjected. Does the increasing transfer of iron from the interior to the surface of the earth exercise any sensible meteorological influence ? Is it in any marked way influential on electric currents, and thence does it affect magnetic storms? This is a question which needs a little thought to answer safely. The development of railways, and the almost universal substitution of iron for wood wherever it is practicable to use that metal, must surely exercise a decided influence of its own. Every year more and more of the iron formerly buried deep in the earth is spread upon its surface, and it is surely reasonable to assume that, electrically, at least, some effect is produced ; how far we may venture, as some seem now disposed to do, to translate this into a meteorological agency is a problem for science to determine. — Knowledge Mr. Stroh, during a discussion at the last meeting of the Society of Telegraph Engineers, described a highly ingenious experiment with the microphone, from which he deduced that " during the time when the carbons are really in what is called microphonio contact, they are not in contact at all, or, at all events, that thore is a repellent action at tho point of contact." In the experimental apparatus one small rod of carbon was attached at one end to an almost Motionless oscillating rod, having on its opposite side an extremely light concave reflector. The other end of this carbon rod fell across another carbon rod, which was fixed. The displacement of a spot of light reflected by the mirror showed that the upper carbon was repelled through l-2000th part of a millimetre.