402 STUDIES ON THE PHENOMENA OF CONTACT. 



comes solid, and without any sensible change of volume. "With a magnifying 

 glass, it is easy to see that no trace of crystallization exists in the globule. It 

 is a limpid drop, and colorless as melted glass. By experimenting in different 

 ways, I ascertained that this limpid phosphorus differs, as regards its chemical 

 properties, in no respect from ordinary phosphorus. It does not, however, 

 take lire when poured out in a still liquid state in contact with the air. This, 

 then, is not an allotropic state of phosphorus analogous to ozone, but a molecular 

 state peculiar to this body. I have satisfied myself that other salts may act on 

 phosphorus like the nitrate of iron. If this colorless phosphorus be melted 

 under water and then exposed to the light, it reverts to the state of ordinary 

 opaque yellow phosphorus." 



Other examples of physical changes, analogous to those just mentioned, are 

 furnished by sublimation of the black sulp buret of mercury, which, by this 

 treatment, becomes red, by the red and yellow iodides of mercury; and since 

 in nature all phenomena are linked with on(i another, these two categories of 

 facts, to wit : the chemical and the purely physical changes induced by contact, 

 arc connected by the phenomena of the explosion of different fulminating pow- 

 ders by mere contact with the barbs of a feather. 



But th(;se two last classes of facts stand somewhat apart from the domain 

 of catalytic phenomena, inasmuch as they are regarded as chemical 'phenomena. 

 Thus my experiments have taught me that phosphorus assumes the limpid and 

 colorless state whenever its refrigeration, after fusion, takes place under the 

 prescribed conditions, whatever may be the liquid Avith which we operate. It 

 is a phenomenon exclusively physical. If certain saline solutions cause it to 

 pass into this colorless and limpid state, it is because the phosphorus melted 

 in these solutions can cool more regularly than in pure water, and because such 

 cooling allows the molecules of phos[)horus to arrange themselves in a position 

 suited to transmit the light entirely without reflecting or dispersing it. The 

 black and o])aque modification of phosphorus, discovered by Thenard, is an anal- 

 ogous though inverted example of a molecular change. 



An analogous case is presented in fibrous iron, when it is made to undergo 

 frequent and prolonged vibrations. There is established in the mass, ac- 

 cording to Pelouze, Liebig, and others, a molecular movement which occa- 

 sions tiie crystallization of the metal ; so that it is not rare to see a bar of iron 

 of good quality slowly transformed under the influence of the vibrations into 

 iron crystallized with large facets. 



Phenomena of this sort belong, as we have seen, to the domain of physics, 

 and have nothing in common with catalytic phenomena. Another order of 

 facts, which more nearly approaches the latter, appears in the case of certain 

 oxides, which, when submitted to a certain degree of heat, become perfectly 

 indijj'crcnt in regard to reagents, giving place to a sort of phosphoresceace. 

 They are then no longer dissolved in acids, or if so, are acted upon with much diffi- 

 culty. This may be referable to a loss of water, sustained by the calcination 

 of these oxides, but it is more probable that these ^\\q\\o\xiq.\\.i o^ indijfcrcn.ee are 

 analogous, but inverse to what is presented by oxygen when it passes into the 

 state of ozone. 



The passiritij of iron, of cobalt, and of nickel — three of the most magnetic 

 metals — app(!ars due, according to recent experiments, to a slight layer of 

 oxide, or another combination which forms suddenly on the surface of the pol- 

 ished nu'tal, and preserves it from the contact of the acid. From some trials 

 which I have lately made, but which arc not complete, I am led to believe that 

 other metals may show the same property in certain conditions. 



Let us pass to the examination of what occurs in catalytic phenomena, 

 properly so called, and let us take as a first example and type the combination 

 of hydrogen and of oxygen under the infiueucc of the presence of platina. This 

 phenomenon is sometimes known under the name of slow combustion, a term 



