TABLE II.

THE HISTORICAL DEVELOPMENT OF GENERAL

CHEMISTRY.*

BY WILLIAM OSTWALD,

PROFESSOR AT THE UNIVERSITY OF LEIPZIG.

FIFTH LECTURE. EQUILIBRIUM AND CHEMICAL AFFINITY. Ladies and Gentlemen: In the beginning of the nineteenth century, the text-book of chemistry which was most used in Germany was one written by von Stahl, the same man who was the originator of the phlogiston theory. From our previous description of the phlogiston theory you will see that von Stahl was indeed a man of the most systematic mind, for he knew how to find the general truth connecting a number of the different factors.

In this same text-book of von Stahl's you will find a page dealing with a most peculiar regularity, one which was first recorded. by him. If you dissolve silver in nitric acid (of course, I could take any other example) and add metallic copper to it, the copper will throw out the silver, i. e., the silver will reappear as a metal and copper will go into solution. If a piece of metallic lead is now brought in contact with the solution it will throw out the copper, and take its place in the solution. And from this solution we can again obtain the lead by treatment with metallic zinc. Further, the zinc solution can be precipitated by throwing in some lime, and from the lime solution you can precipitate the lime, i. e., as carbonate of calcium, by adding carbonate of ammonium, which was a well known preparation at that time. And, finally, by treating this solution in its turn with potash, and heating, the ammonia can be expelled. In this way we find that there exists a series of different compounds and different substances, or elements, as they were considered at that time, which is so made up that each succeeding member in the series will throw out or precipitate or cancel from the combination the previous members. von Stahl especially pointed out in this connection that the third or fourth member

*Course of six lectures delivered in the Department of Chemistry of Columbia University, Havemeyer Hall, January 26 to February 2, 1906. Reported stenographically. Lectures 1 and 2 were printed in the January, 1906, number; lectures 3 and 4 in the April, 1906 number. Copyrighted by the SCHOOL OF MINES QUARTERLY.

will throw out the first, just as in our example the second member did. This series was called later the series of affinities.

von Stahl laid great stress on these facts and particularly recommended his readers to consider the series and the facts connected with it as exhaustively as possible, because the great secret of chemistry lay hidden in it. This idea of a series of affinities or a series of reactions of a similar kind was then taken up in a later time by the French chemist Geoffroy, who did not add much to this idea of von Stahl's, but simply tried to arrange all known substances (there were not very many at that time) into such a series, which he published as an affinity table. In the history of chemistry you will find that Geoffroy, only, is mentioned as the inventor of the affinity table, although he simply acknowledged and amplified the older idea which belongs to von Stahl, so far as my historical investigations go. But, of course, it is not impossible that someone even antedated von Stahl in the recognition of the law, although if so I cannot find any mention of it.

Now investigation showed that such a simple table was not to be made; it appeared that several of the reactions that went on in a certain way in aqueous solutoins, or in the wet way, as it was called at that time, were to be arranged in an entirely different order when the substances brought into contact were not dissolved, but molten; so that instead of the one table of affinity it was necessary to construct at least two tables, one for reactions in the wet way and the other for reactions in the dry way, i. e., produced by the application of heat.

And further, the number of known substances increased so rapidly that Bergmann, who tried to work out the whole chemical. theory of these reactions of decomposition, found himself in the face of an overwhelming number of necessary experiments if he were to prepare a complete table of affinity which would explain or enable us to predict possible reactions. Of course, in addition to these there are many possible combinations between two known substances, and, as I remember, Bergmann computed the number of experiments necessary to be carried out to be 20,000

or so.

At the same time Bergmann tried to get a general expression for the behavior of chemical substances decomposing into others, and to express the general relations of these things. He considered that chemical reactions were brought about by the same

force which moves the heavenly bodies, by general attraction or gravitation, and concluded, therefore, that the method of investigation should be the same. If there were two different atoms, there must be a certain attraction between them. And if a certain atom intervened which has a stronger attraction to one of the two atoms than to the other, the stronger attraction must prevail, and the weaker atom be thrown out entirely, so that the new combination will contain only the atoms with the stronger attraction.

You see this is a very simple theory and proved sufficient and satisfactory at the same time, for it was then generally supposed that all chemical reactions took place in this absolute way. This was the state that existed at the end of the nineteenth century, and Bergmann's theory, as based upon these different attractions was quite well known. It was certainly a most picturesque theory, and if you would like to get a more detailed idea of it I would refer you to the work of Gerhardt, in which he uses this idea of Bergmann's of the mutual attraction of the different bodies, and describes with much vigor the irresistible force of their attraction, independent of any former union or former combination.

This theory looked beautiful, however, only because people omitted to consider the cases which disagreed with it, for it was found to be quite impossible to arrange all reactions in a systematic table; and, indeed, you will find in the periodicals of that time that even then a little fun was made of the authors of these inverted tables, although generally, it must be said, it was considered as the leading theory in chemistry.

Then a man, whose name I mentioned several days ago, made a considerable advance. This was Berthollet, who developed some new ideas of his own which proved much more exact and more fitted to the present facts than these older ideas of the relative affinity. Berthollet was induced to investigate these things by rather a rare circumstance. He was taken by Napoleon the First to Egypt in that romantic expedition at the beginning of Napoleon's brilliant career. Napoleon took care to take with him a great number of scientists to investigate Egypt in every line, and to contribute to his library beautiful large volumes descriptive of Egypt, which were later published by the French government. Berthollet, as one of this band of scientists, observed the formation of soda in the desert, i. e., observed how it came out of the soil by drying, by efflorescence, being formed, evidently, from common salt. This

induced Berthollet to wonder how common salt could be changed by these natural circumstances into soda, and as a result of this he discovered that it was efflorescence that caused the salt to separate out. Then he worked along these lines, reading papers descriptive of his investigation in the Institute of Egypt, established by Napoleon at that time, and finally finding that there are quite a number of different cases where well known reactions could be inverted, i. e., forced to take place in an inverse way.

And these facts induced him to entertain the following idea. He said those specimens of chemical affinity of the old chemists were due to mutual attraction or some similar reason, as gravity, but, just as two forces never destroy one another entirely, in the same way an antagonistic chemical force could not destroy another entirely, and some intermediate step between the action of the two forces must always result. If we have two acids, for example, fighting for an insufficient quantity of a base, it would not be like two dogs fighting over a bone, that one gets the bone and the other gets nothing, but each one would get a portion of it, the stronger acid getting the greater part and the weaker acid the lesser; but the weaker acid would never be dismissed without getting at any rate a little bit of the base.

By this general idea he explained precipitation and affinity. It is just as if we should describe in our time the influence of a new phase. You will remember the phases that we discussed in our first lecture. By the formation of a new phase the equilibrium existing in the first phase is disturbed, but the quantity of any phase does not change the equilibrium law. If, for example, we have a million pounds of ice and water in equilibrium, and take from the water or the ice, or add any quantity of water or ice, the equilibrium will not be disturbed. But if there are gases being given off in the form of bubbles, that gas will be leaving the field of battle, and not taking part in the formation of a new phase. A partition between the possible compounds, then, can be made to look like an absolute change, an absolute decomposition. He explained, for example, if you add some acid to a solution of car. bonate of potash, there will be the partition of the potash between the carbonic acid and the acid, for example, acetic acid, but as the carbonic acid would assume the gaseous state and escape, the equilibrium would be disturbed. More carbonic acid will then be formed in the liquid, and be in its turn changed into the gaseous

VOL. XXVII.-28.