STUDIES ON THE PHENOMENA OF CONTACT. 401 



Among the phenomena commonly cicsignatecl by the term phenomena of con- 

 tact or catuhjt'tc phenomena, we may mention, a3 one of the most remarkable, 

 the discovery in 1817, by Sir II. Davy, that a wire of platina will continue 

 incandescent in certain gaseous mixtures. He observed, in this manner, the 

 slow combustion of alcohol, of ether, of spirits of turpentine, of the oil of naphtha, 

 of carburetted hydrogen, &c. lie found, still later, that palladium possessed 

 the same property. Some years afterwards, M. Doebereincr invented his hydro- 

 gen light apparatus, in which he employed spongy platina, and nearly at the 

 same time Thenard observed the curious and apparently inexplicable phenomena 

 which are exhibited when oxygenated neater is added to certain oxides, such as 

 the oxide of silvei*, &c. Dulong and Thenard subsequently studied the cata- 

 lytic influence o? palladium, (previously noticed by Davy.) o? rhodium, oi iri- 

 dium, of gold, of silver, of nickel, and even of substances of a different nature, 

 such as charcoal, pumice-stone, porcela.in, glass, and ro(-k crystal. Still later, 

 Th. de Saussure announced that certain organic bodies, such as humus compost, 

 wheat,* cotton, silk, and lignine, possess properties analogous to those of the 

 bodies previously named. He observed that these bodies effect a diminution 

 of volume in a mixture of oxygen and hydrogen, and that the volume which 

 disappears is In the proportion requisite to form water. MM. Mitscherlich, 

 Faraday, Reinsch, Boettger, Millon, and others, have still further enlarged th«! 

 field of catalytic phenomena. According to M. Reinsch, fibres of asbestos, when 

 gilded or plated, exhibit all the phenomena which have been remarked with 

 wire of platina or palladium, and it is nearly the same if these fibres be covered 

 with iron, nickel, cobalt, or lead. M. Bosttger thinks that it is not always the 

 metal, but often its oxide, which is the active body in these latter cases. He 

 covered fibres of asbestos with oxide by plunging them in the solution of a 

 metallic salt, then in ammonia, whence they were rapidly passed through boiling 

 water, and were heated to redness in the llame of an alcohol lamp. It results, 

 then, that the oxides of chromium, iron, nickel, maganese, &c., act like the 

 platina wire of Davy. One of the last labors of the illustrious Thenard proved 

 that in the case of any body whatever capable of disengaging a gas by heat, 

 suc?i disengagement always takes place at a lower temperature xchen a iliird 

 body, a metal, an oxide, Sfc, is added, although wc are sure that this third body 

 takes no part in the reaction. The presence of chijjs of beech-wood in the 

 manuf'icturc of vinegar is another example of the phenomena with which we 

 are engiged. Yeast and the cognate bodies may be placed in the same class. 



In all these instances it is chemical changes which are in question ; the 

 combinations and decompositions of bodies. But contact may sometimes deter- 

 mine changes exclusively physical; as, for example, in the sudden crystalliza- 

 tion of a saturated solution of sulphate of soda by the contact of a slip of glass. 

 In 18-50 I discovered that certain saks might eftect the same molecular change 

 on the phosphorus which Woshl r had observed in fu^^ing ordinary phosphorus 

 in a mixture of sulphuric acid aud bichromate of potassa. These are salts 

 whose cold solutions phosphorus does not decoinpose, or at least decomposes but 

 slowly. The following is what I stated at that tim^ : " It is a very remarkable 

 fact that certain salts, Avhose cold solutions phosphorus docs not decompose, 

 appear to exert a pecu'iar action on it, causing it to undergo a molecular modifi- 

 cation. If a portion of opaque reddish pho-phorus be placed in nitrate of iron, 

 diluted by about once its own volume of water, no chiunical action is remarked 

 even after a long space of time. If the whole be then heated until the complete 

 fusion of the phosphorus is effected, and the tube with which we operate be then 

 removed to a quiet place, the phosphorus Avill remain liquid a long time, and 

 on decanting the liquor, will suddenly become solid, resembling, in all respects, a 

 globule of melted glass. In decanting the salt after cooling, the liquid phosphorus 

 will sometimes flow off with the solution. If after receiving the whole on filtering 

 paper, we touch this liquid phosphorus with .1 rod of glass, it suddenly be- 

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