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FIG. 5. Behaviour of Fatty Oil under Influence of Enzyme.

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No evidence of the production of cyanate during the hydrolysis of urea by urease has been obtained.

It is of interest that, whereas ammonic thiocyanate can be destroyed by bacterial action, thiourea cannot; this compound is not known to undergo change in solution.

Before leaving the subject of catalysts, the rusting of iron may be referred to as a case in which the action is influenced by a particulate agent. The subject is one of perennial interest and it is strange how slowly the nature of the process is appreciated. It must be electrolytic; the metal is attacked primarily in a circuit comprising the electro-negative conducting impurity present in all irons and the electrolyte on its moist surface, usually carbonic acid, the product being a soluble ferrous salt. If this salt remain at the surface, it necessarily undergoes hydrol- ysis yielding ferrous hydroxide, which is deposited as solid and sooner or later oxidized to a ferric hydroxide. J. A. N. Friend has recently advanced a " colloid theory " in explanation of the process. He shows that in moving water there is little rusting, though the iron is slowly dissolved as must be the case on the above view. He considers that the ferric hydroxide precipitated on the surface under still conditions acts catalytically, by oxidizing metallic iron with relative rapidity and simultaneously undergoing reduction to a lower hydroxide, etc. It is well that this effect of once formed rust should be insisted on; but it stands to reason that it should act as an accelerator, by pro- moting, through the surface action of its fine particles, the con- densation both of electrolyte and of oxygen, whether or no it act itself and be alternately reduced and reoxidized.

The part played by the determinant in gaseous interactions has yet to be appreciated. The results obtained by Bone and his co-workers at high pressures are specially significant. When a mixture of hydrogen and oxygen, diluted with nitrogen, is exploded, the pressure rises to a maximum almost immediately; if methane or carbonic oxide be burnt in place of hydrogen, the pressure developed rises to a maximum only gradually. The process of change must be far more complex in the latter cases. The slowness of the change, in carbonic oxide, may reasonably be ascribed to the prior conversion of the oxide into formic acid (CO+OH 2 =H 2 CO2) before it is burnt (cf. Trans. Roy. Soc., 1915, A. 215, 275).

Whatever the phenomena considered, if the view be taken that chemical change is essentially an electrolytic process, con- clusions such as have been formulated cannot be avoided. The process, in the main, isthe same in all cases. The " determinant " is the cause of change; when a catalyst is present, the rate of change is greatly accelerated, owing to the concentrating effect this exercises; maybe, in some cases, the catalyst is required together with the determinant to constitute a conducting circuit of the interacting materials.

It is strange that the action of the determinant is so much over- looked. Recent observations by H. B. Baker show that its influence is to be considered even in cases of chemical change not ordinarily regarded as such the evaporation of liquids. Long ago it was proved by him, that not only do hydrogen chloride and ammonia not interact when dry but that the product of their interaction, ammonium chloride, does not decompose so readily, when heated, if dried. He now finds that as liquids, such as benzene and bromine, are rendered more and more nearly dry, the boiling point rises and at the same time the weight of the molecules in the liquid gradually increases. Strange to say, when shaken with water, the polymerized benzene only slowly passes back into the simpler state.

As the phenomena of chemical change are more and more closely examined into, the conviction grows that molecular structure and affinity are the determining causes; to correlate these with the electronic structure of the constituent materials is the difficult task of the coming generation. Why is carbon so entirely peculiar an element? Why has oxygen so remarkable an influence on the development of acidic qualities? An endless series of such questions may be asked. They must be answered in terms to satisfy the chemist to satisfy his dynamic as well as his structural cravings, and to explain the many variations in function which follow from variations in composition.

A revolt is now setting in against the tendency to accept purely physical interpretations of chemical phenomena, which has so long been prevalent and has too often led chemists to overlook the complexity of the conditions prevailing in solutions. As a result, undue importance has been attached to mathematical agreements which it is clear have but served to give colourable expression to the facts; and the minute and penetrating analysis