Since the publication of the second part of the first volume, (1810) some important essays on the subject of heat have appeared, which have a direct bearing upon some points of the doctrine on that subject inculcated in the said volume. It may be proper to state the results, with such remarks and reflections as have occurred in the consideration of them.

In the Annales de Chimie for January 1813, also in the Annals of Philosophy, vol. 2, we find a Memoir on the specific heat of different gases, by M. M. De la Roche and Berard. This exhibits a most laborious and refined series of experiments on this most difficult subject. Great merit seems to be due to them, both for invention and execution.

It is unnecessary to describe the particulars of the apparatus and the mode of conducting the experiments, as a description may be found as above referred. It is sufficient to observe that the calorimeter used was a copper cylinder of 3 inches diameter and 6 in length, filled with water, and having a serpentine tube 5 feet in length, running through the interior and opening at both ends on the outside of the vessels. By means of this tube a regular current of any gas of a given temperature (212°) might be passed through the vessel so as to part with its excess of temperature to the water.

The work now submitted to the public was begun to be printed in 1817; and the 13th and 14th sections, containing the oxides and sulphurets, were printed off before the end of October of the same year. The printing of the rest of the work to the appendix was finished in September, 1821. One sheet of the appendix was printed at the end of 1823; but no addition was afterwards made till May, 1826; when the printing was resumed, and has been continued to the present time.

It may be asked, what were the motives for such a plan of procedure. To this it may be replied, that soon after the publication of the first volume (in 1810), I began to prepare materials, and to institute experiments, relating to the oxides, &c, with occasional diversions into other departments of chemistry, as circumstances arose. As a great portion of my time was always necessarily engaged in professional duties, and as that part of the work I was about to commence was one running into detail, I thought it would be best to print it as I proceeded, whilst the train of thought and of experiments was fresh in view. The advantage in this case was expected to be partly at least counterbalanced by the loss of discoveries and improvements likely to be made in the interval between the printing and publishing of the several articles.

SECTION 13

METALLIC OXIDES

All the metals are disposed to combine with oxygen, but the combination is effected more easily with some than with others; the compound is usually called an oxide, but in some instances it is also called an acid. The same metal combines with one, two, or perhaps more atoms of oxygen, forming compounds which may be distinguished according to Dr. Thomson, by the terms protoxide, deutoxide, tritoxide, &c.

Such however is the repulsion of oxygen to oxygen that we rarely find three atoms of it retained by a single atom of any kind; and there are not many instances of metals capable of holding two atoms of oxygen. Various modifications of the proportions of metals and oxygen arise from the combinations of the oxides themselves one with another and with oxygen, so as to lead some to imagine that an atom of metal in some instances combines with 3, 4, or more of oxygen. This is altogether improbable: It is much more simple to suppose that one atom of oxygen connects two or more atoms of protoxide, 1 of protoxide unites to 1 or more of deutoxide, &c. These intermediate oxides are in few if any instances found to combine with acids like the other two oxides.

There is no reason that I am acquainted with for disbelieving that oxygen combined with a metal is still repulsive of oxygen, and that by the same law as particles of an elastic fluid; that is, the repulsion is inversely as the distance of the centres of the atoms.