Page:Popular Science Monthly Volume 75.djvu/45

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Catalysis, Colloids and Chemical Purity.—When chemical change can be produced in a system by the mere presence of small quantities of another substance which itself usually remains unchanged at the end of the process, such an effect is called catalysis and the agent employed a catalytic agent. Of the varied aspects of catalytic processes we have different examples in the decomposition of substances by the presence of finely divided metals like platinum or colloidal nickel, in the rapid evolution of oxygen from potassium chlorate when a small quantity of manganese dioxide is present, in the solution of insoluble chromic chloride through the mere presence of chromous chloride, in the inversion of cane sugar by acids, in the saponification of fats and esters, in the synthesis of indigo by oxidation of naphthalin, in the standard manufacture of sulphuric acid in the leaden chambers and the later improvements of the method through the presence of platinum or ferrous oxide, in catatyptic photography without light, in the reversible physiologic and therapeutic action of the animal and vegetable ferments and enzymes, in the synthesis of nuclein during the development of the embryo, and in the pathologic effects of poisons, venoms Mid the toxins of disease. Many theories of catalytic action have been advanced, of which the earliest and most original is that of Leibig. Liebig supposes catalysis to be due to the fact that the catalytic agent has power, like that of a tuning fork, to set up sympathetic molecular vibrations in the substance acted upon, producing chemical change. This theory has been proscribed by Ostwald because, being a figment of the mind, it is neither capable of proof nor susceptible of refutation, leading the subject into a blind alley, from which further scientific advance is impossible. It has therefore remained, like Hamlet's father, "quietly inurned," as a beautiful, imaginative hypothesis which we can neither prove nor disprove. Of other theories of catalysis the most important is that of Ostwald himself, summed up in his famous definition: A catalytic agent is one which modifies the velocity of a chemical reaction without appearing in its final process. This statement introduces two new ideas, the notion of infinite swiftness and infinite slowness in chemical change and the fact that catalytic change may be brought about by a series of intermediate reactions. It will be seen that Ostwald's definition is elastic enough to include as