CHEMISTRY. 



101 



phosphorescent, owing to its rapid oxidation 

 in contact with moist air, and will even shine 

 under water that contains air. In oxygen it 

 is a little more brilliant, but shines most viv- 

 idly in highly-ozonized air. 



In phosphorescent animals noctilacine is se- 

 creted by a special organ. Under certain con- 

 ditions of temperature and humidity it is also 

 generated by dead animal matter, flesh, blood, 

 and sometimes urine. Whatever its source, its 

 light is the same. It is monochromatic, gives 

 a spectrum mainly visible between the lines E 

 and F, and possesses always the same chemical 

 properties. The Scolopendra electrica secretes 

 ooctilucine in a state of comparative purity, 

 and, by making several of these myriapods run 

 about over a large glass capsule, in the month 

 of September, a sufficient quantity may be ob- 

 tained for examination and analysis. It can 

 also be obtained, though less pure, from glow- 

 worms and the phosphorescent surface of dead 

 fish, by scraping the luminous matter on to 

 damp filter-paper. 



The secretion of noctilncine by the superior 

 luminous creatures, such as insects (Lampyrut, 

 Elater, etc.), is doubtless up to a certain point 

 under the influence of the nervous system, so 

 that they have the faculty of causing their 

 light to cease at will, in which case the secre- 

 tion is arrested for the time ; but glowworms' 

 eggs continue to shine for some time after 

 they have been laid, so that they mast also 

 contain a small quantity of uoctilucine. In 

 the lower orders of animate beings, such as 

 tha little Noctiluca miliaris of the English 

 Channel, the flexible polypi, etc., there is also 

 no doubt of the existence of a special organ for 

 the production of the light ; and, where there 

 are scarcely any indications of a nervous sys- 

 tem, the secretion of the material appears fre- 

 quently to be susceptible to the influence of 

 external circumstances. 



The must sensitive thermo-electric pile fails 

 to detect the presence of heat in the rays of 

 light emitted by noctilucino under any condi- 

 tions. 



Decompotitian of Explotivet and the Phe- 

 nomena of Supertaturation. During the past 

 year Messrs. Champion & Pellet have contin- 

 ued their researches on explosives, and from 

 time to time communicated their results to the 

 Aead6mie des Sciences. In one of these contri- 

 butions they compare the mode of decompo- 

 sition of explosive bodies with the phenomena 

 of supersatu ration. The name of explosives is 

 commonly given to compounds or mixtures 

 which under various circumstances disengage 

 a volume of gas whose rapid formation causes 

 an explosion. In certain cases, as in the pow- 

 ders whose type is gunpowder, the explosion 

 is produced by combinations which take place 

 between the component elements. In others, 

 as in substances of indefinite composition, such 

 as the ethers of the monatomic and polya- 

 tomic alcohols, the fulminates, the compounds 

 of nitrogen with several non-metallic elements, 



etc., the explosion results from the violent 

 separation of the elements. This definition 

 appears limited to a restricted number of phe- 

 nomena, whence the authors have concluded 

 that, in order respectively to distinguish bodies 

 with regard to their rapid decomposition, a 

 classification into stable and unstable would 

 he more appropriate and comprehensive. From 

 this point of view we might designate as un- 

 stable the bodies or compounds in which the 

 equilibrium, if broken in one point and under 

 given conditions, determines the immediate 

 decomposition of the whole mass with a rapid- 

 ity and an evolution of heat depending on the 

 nature of the body and on the circumstances 

 to which it is exposed. A great number of 

 unstable bodies can manifest their change of 

 state either by a rapid decomposition giving 

 rise to a true detonation, or by the more grad- 

 ual separation of the component elements. 

 Dynamite and gun-cotton, which can be de- 

 composed by ignition, flame, or a violent 

 shock (such as that of a detonator), present a 

 striking example of these facts. The authors 

 have sought to establish precise analogies 

 between the phenomena which accompany the 

 different modes of action of supersaturated 

 solutions, and of unstable compounds; among 

 the latter they have selected dynamite on ac- 

 count of the facility witli which it undergoes 

 decompositions of different grades. Supersat- 

 urated solutions may be considered as unstable 

 compounds of water and of a hydrated salt or 

 its isomorphs. This crystal represents the de- 

 tonating primer which effects the rapid de- 

 composition of nitro-glycerine. In fact, while a 

 few decigrammes of fulminate of mercury in- 

 duce the explosion of dynamite, iodide of 

 nitrogen, sufficient in quantity to be mechani- 

 cally equivalent to the fulminate, is unable 

 to explode the dynamite. With a suitable 

 charge of fulminate of mercnry, dynamite ex- 

 plodes, whatever its quantity or whatever the 

 form of the containing vessel. A sufficient 

 weight of sulphate of soda, at ordinary tem- 

 peratures, determines the crystallization of 

 supersaturated sulphate, even in those cases of 

 " desensibilization " which will be examined 

 below. The diameter of the tubes containing 

 the sulphate of soda or the shape of the re- 

 cipients is without influence on the speed of . 

 crystallization. If the primer is insufficent, 

 the dynamite undergoes only partial decom- 

 position, and in certain cases does not ignite. 

 Supersaturated sulphate of soda presents dif- 

 ferent crystallizations, resembling the modes 

 of action of the primer. Solutions crystal- 

 lizing under the influence of sulphate-of-soda 

 particles contained in the air yield long crys- 

 talline needles. But, if large crystals of the 

 sulphate be introduced, the crystallization is 

 confused, and the crystals appear partly 

 broken. An inert body (silica, etc.) added in 

 excess to nitro-glycerine completely modifies 

 its sensibility, and transforms it into a com- 

 pound which resists even energetic shocks. A 



