should have a series of experiments, which, if rightly compared, would not only disclose the various properties of each, worthy of observing, but would determine also the relative quantities. In this way, if the absolute value of only one were diligently sought out, all the rest would follow.

Vol. ii., p. 373. "The calces of metals have not that amount of phlogiston which is necessary to the metallic condition, but they are still found not entirely deprived of it.

"Metallic precipitates, when properly examined, reveal to us various mysteries."*

"In the following table 100 parts of reguline metal are in all cases understood to be dissolved :— †

100 parts of Gold with the aerated mineral alkali gave 106 of dry precipitate.

100 parts of Bismuth with the aerated mineral alkali gave 130 of dry precipitate.

66

99

aerated mineral alkali

phlogisticated

aerated mineral alkali...... 180

caustic phlogisticated

Having compared the weights now produced, it is necessary, first, to inquire into the cause of such differences."

* * * Is it not then the matter of heat that is attached to the calx, and which is always united to the caustic alkali, for does it not excite heat when dissolved in the simple acids ?

"This forms a triumphant foundation for assaying minerals and metals in the humid way, the mere weight of the precipitates being known. If the same mode of operating be used, the results of the experiments will be always the same. Let us say that a quantity of metal a in certain circumstances makes a precipitate of the weight of b; if the same method be used, it is obvious that nb may safely be allowed to correspond to na of the perfect metal, although in the fundamental experiment, the dissolved metal may not have been completely precipitated, or its weight may have been increased by foreign matter, still the same circumstances will produce always the same gain or loss, and the conclusion

will remain unshaken. Let then the methods be exactly decided on, and no fallacy is to be feared." *

66

ON ELECTIVE ATTRACTIONS.

Simple elective attractions.† Let A be the substance to which a, b, c, &c., are drawn; further, let A be added to c to saturation, this we shall call Ac, when again b is added, let the union take place to the exclusion of c; then A is said to attract 6 more than c, or b has a stronger elective attraction than c; then Ab, when a is added, gives up b, and a is united instead, then it is understood that a excels b in attractive force, and the order of the efficacy of the attraction forms a series a, b, c. What we here call attractions, others call affinity; we use either term promiscuously in future, although the latter being more a metaphorical expression does not appear so suitable in physics.

*

Page 318. "It has not escaped me, that some chemists have considered, as entirely without foundation, the doctrine which asserts that neutral or middle salts can receive a distinct excess of acid. That this sometimes takes place the experiments to be related most clearly shew, although naturally it (the excess) adheres with far less tenacity than that portion which is necessary to effect saturation.

* Page 325. "From all that has been brought forward, I consider it clear, not only that the doctrine of a decided superfluity of either ingredient is not absurd, but that in reality this result is found in many cases. Certainly this superfluity attaches itself much more loosely than the portion necessary for saturation, so that frequently it is easily driven off, but this in no way causes it to be less real."

He

Here we find Bergman endeavouring to obtain the amount of oxygen in metallic oxides, or phlogiston in metals. finds that the amount in equal quantities of metals is not the This could only be the case if the atomic weights of

same.

all metals were the same.

*

Page 396.

† Vol. III., page 294.

In agreement with this, he finds that the quantity of acid necessary for dissolving certain weights of metals, differs with each metal, and the amount which one metal precipitates from the solution, differs with each metal. This was promising fair for discovery; and in the first table we have the amount of various metals needed to precipitate 100 of silver, in fact, a table of atomic weights, if he could have seen it, although imperfection in experiment rendered it difficult, and the law seemed very intricate.

He drew the conclusion that some acids dissolve metals with more oxygen in their oxides than others, when he says, 100 of silver are reduced by 31 of copper in nitric, and 30 of copper in sulphuric acid. This helped to lead him wrong. He seems to have most naturally thought that it would be needful to find the relation of the oxygen in a metallic oxide to that in every other, and was naturally surprised at the great labour needed. We know that this would be a most complicated relationship, and that the oxygen is constantly changing its per centage relation in every compound, to such an extent, that it would be impossible to follow it without constant recurrence to its atomic weight. We may look on this inquiry of Bergman as a search, acute although unsuccessful after that last step in simplicity.

He gives a valuable discovery in the establishment of the permanence of the amount of oxygen in precipitated oxides, the very foundation of analysis, and an important step towards the knowledge of permanence of constitution in all substances whatever. That the numbers need correction, need hardly be remarked.

At the same time it seems to be beyond doubt that he did not grasp with great clearness the doctrine of permanent constitution, or he would scarcely have made these remarks on neutral salts receiving a distinct excess of acid. Any indefinite amount added, becomes a mixture only.

He extended the tables of attraction to a great length,

calling them elective attractions, preferring attraction to affinity. His tables are 59 in number, the first portion giving the wet way, and the second the dry. These were given in the old symbols, and have certainly a most formidable and unattractive appearance, in his original work. They have, however, been published in England, at an early period, in the form below.

SINGLE ELECTIVE ATTRACTIONS.