acids of the third group produce in the corresponding reaction an evolution of heat. (7.) The tribasic acids exhibit differences similar to those of the bibasic acids, citric acid belonging to the second group, arsenic and orthophosphoric acid to the third. Thus we have Hence the second or third molecule of sodic hydrate evolves with citric acid more, with arsenic and ortho-phosphoric acid less heat than the first molecule. The difference in the evolution of heat in the second and third molecule of sodic hydrate is besides very large for arsenic and phosphoric acids. (8.) The three groups which I have established in the class of bibasic acids, and of which two are found also in the class of tribasic acids, have their probable origin in the different constitution of the acids. In fact in the case of a bibasic acid the position of the two atoms of hydrogen replaceable by sodium may be conceived in three different ways. Thus sulphuric acid may be expressed by the following three formulas: ( ᎾᎻ ᎾᎻ The first formula might be most probable if the acid were a hydrogen acid; the second is most probable for an acid whose anhydrid exhibits a slight affinity for water; the third is the formula of a bibasic hydroxylic acid. The constitution expressed by the first formula probably corresponds to that of a bibasic hydrogen acid, as for instance fluosilicohydric and chlorplatinhydric acid. SH Н 6 Sulphurous, selenious, carbonic, chromic and boric acids probably correspond to the second formula. Of these the first four at least easily and spontaneously split into anhydrid and water, so that the hydrates (acids proper) of several can scarcely be prepared at all. We have therefore for the rational formulas of these ᎾᎻ acids, See 2 H ᎦᎾ2 · H ᎾᎻ €2. H' &c. This corresponds entirely with the behavior of the homologues of carbonic acid, like glycolic acid and the other members of the lactic acid series, which are probably diatomic, but usually appear monobasic, as the second atom cannot be easily replaced by sodium, but readily by alcoholic and acid radicals. To the third formula correspond sulphuric, selenic, oxalic and tartaric acids, the formulas of which according with the usual assumption, become as follows: ᎾᎨ ᎾᎻ ᎾᎻ The analogy of the tribasic and bibasic acids leads for citric acid to the formula, H. 3OH, while the formulas for the three modifications of phosphoric acid would be the following: 6 ᎾᎻ ᎾᎻ 2HP3 H ᎻᏢᎾ 3, by which the thermic difference between citric acid and the acids of phosphorus and arsenic may be explained in harmony with the prevalent chemical theories. (9.) Silicic acid is given in the tables (accompanying this paper) as a bibasic acid, but differs materially from the other acids of this group, by being absolutely without any definite point of neutralization. The numbers of table II show, it is true, that the heat which a molecule of the acid evolves with an increasing quantity of soda, increases only very slightly when this exceeds two molecules of sodic hydrate, and table I shows that the evolution of heat increases approximately in proportion to the quantity of acid, until this amounts to molecule of silicic acid for one molecule of sodic hydrate. But table II shows at the same time that the numbers by no means increase in proportion to the quantity of soda, and table I also shows that the evolution of heat increases very materially for further additions of silicic acid. From what was shown in Section IV (Pogg. Ann., Bd. 137, p. 203), it appears that the maximum of heat which a molecule of sodic hydrate can evolve with silicic acid, and which occurs only when the quantity of acid is infinitely great, amounts to 134.. while for molecule of silica it is only 26..; further, that the maximum of heat which is evolved by the action of a molecule of silica upon sodic hydrate, and which also occurs when the quantity of sodic hydrate becomes infinitely great, amounts to only 63.. while two molecules of sodic hydrate already evolve 52... (10.) The anomaly in the neutralization of silica has very probably its cause in the simultaneous action of water and silica upon sodic hydrate. According to what has been said under 4, water is to be regarded as a monobasic acid, and sodic hydrate as its sodium salt. If now the sodium salt is attacked simultaneously by the two acids (water and silica), the base divides itself between the two acids in a ratio which depends upon the avidity of the acids and their quantity, (see Sect. 1, Pogg. Ann., Bd. 138, p. 94). If now the avidity of the water for the base is very small in comparison with that of the acid, this decomposes an approximately equivalent quantity of sodic hydrate, and the evolution of heat becomes therefore approximately proportional to the quantity of acid, as is also approximately the case with all other acids. If, on the contrary, the avidity of the water for the base is a quantity which cannot be neglected in comparison with that of the acid, the proportionality in the evolution of heat ceases, and then follows a law which holds good for partial decomposition, (see reference cited). The absorption of heat which takes place when a solution of sodic silicate (and also various other saline solutions) is diluted with water, has probably its cause partly in a partial decomposition of the salt by the water. (11.) The quantities of heat evolved in the reaction of one molecule of sodic hydrate with one molecule of acid-hydrate in aqueous solution are very different. Fluohydric acid gives the greatest amount of heat (163..); then comes sulphurous acid (159..), hypophosphorous acid (152..), arsenic acid (150..); the different phosphoric acids, phosphorous, selenious, selenic and sulphuric acids give between 148.. and 144.. The evolution of heat is less in the cases of the hydrogen acids of chlorine, bromine and iodine and nitric acid (137..); much less in the cases of boric and carbonic acids (110.. to 111..) while sulphydric, silicic and cyanhydric acids give the smallest amounts of heat. If however we compare the evolution of heat which a molecule of sodic hydrate produces with the quantity of acid necessary to form a normal salt, the order of the series is somewhat different, but here also fluohydric acid occurs with the greatest quantity of heat (163..); then follow sulphuric, selenic and hypophosphorous acids (155.. to 152..), then sulphurous, hyposulphuric, phosphorous and oxalic acids (145.. to 141..), and so we pass gradually down to sulphydric, cyanhydric and silicic acids. (12.) For some of the acids which I have studied the heat of neutralization had been determined already. The older investigations often show material differences from the numbers determined by me. The determinations of Favre and Silbermann in particular differ greatly. The results of these investigators for chlor-, brom- and iodhydric acids and for nitric and phosphoric acids are from 10 to 12 per cent too high, for instance for the first four acids 151.. to 152.. instead of 137... The cause very probably lies in the inaccurate indications of the mercurial calorimeter employed by them, and I doubt very much whether the experiments recently made with the same apparatus possess a greater accuracy. I have already found several material errors in the published results to which I shall return hereafter. For the rest I refer, with reference to the inaccuracy of the results obtained with mercury, to my communication in the Reports of the German Chemical Society at Berlin, 1869, p. 701. II. GEOLOGY AND NATURAL HISTORY. W. G. 1. Notes on the American Mastodon and other fossils; by Dr. J. LEIDY (Proc. Acad. Nat. Sci. Philad., Sept. 1870).-Dr. Leidy, after brief notes on the specimens of Mastodon in Boston and Cambridge, makes the following observations on some bones in the Museum of Amherst College. Prof. Shepard has recently collected together many interesting fossil remains of vertebrates. Among these are a multitude of specimens obtained by his son from St. Helena Island, and the famous Ashley River deposits of South Carolina. Those from the latter locality consist mainly of Zeuglodons, Cetaceans and Fishes, but also include remains of Mastodon, the Elephant, and of Equus Major and E. fraternus. The St. Helena Island fossils consist of bones, fragments of jaws and teeth of the Mastodon. Among them were noticed two inferior tusks, which measured about ten inches in length and two inches in diameter at the base. The same collection contained a large molar of the American Elephant, of the coarse plated variety, from California. Some remains of Mastodon from the latter place struck me from their peculiarity, and these Prof. Shepard was so kind as to loan to me for examination and description. One of the specimens, which lies on the table, is the fragment of a tusk from "Dry Creek," Stanislaus Co., California. It indicates a species totally different from the American Mastodon, and in its peculiarities exhibits a relationship with the Mastodon angustidens of the middle tertiary period of Europe. The fragment is six inches in length, is slightly curved in two directions, and in transverse section is ovate with the anterior pole acute. The pulp cavity, opening half the diameter at the broken base of the specimen, extends about half its length to the end. The convex side of the tusk possesses, as in Mastodon angustidens, a broad band of enamel, which reaches from the acute edge more than twothirds the depth of the surface. The enamel is somewhat rugose and is two-thirds of a line thick. At one spot, toward the smaller end of the fragment, it has been irregularly worn through for the extent of about an inch and a half. The opposite side of the specimen, from the acute edge, has been worn off to an extent about equal to two-fifths of the surface. The broken ends of the fragment exhibit very conspicuously the beautiful arrangement of decussating curved lines so characteristic of the ivory in the tusks of the great proboscidians. The vertical diameter of the base of the fragment is 28 lines, the transverse diameter 19 lines; the vertical diameter at the opposite end is 22 lines, the transverse diameter 16 lines. The entire length of the tusk appears to have been less then two feet. The question arises as to what species the tusk fragment shall be attributed. It certainly does not belong to the common American Mastodon, nor is it probable that it belonged to the pliocene Mastodon mirificus. May it probably pertain to the hardly known Mastodon obscurus? In the present uncertainty I would look on the specimen as characteristic of a peculiar species allied to the M. angustidens of Europe. For the name of the species I would propose that of Mastodon Shepardi, in honor of Prof. C. U. Shepard, whose name has so long been identified with the interests of natural history. The second specimen, exhibited to the members, consists of a fragment of a lower jaw containing the last molar tooth, and was discovered in Contra Costa county, California. No information in regard to the age of the deposit, or the character of the locality in which the fossil was found, accompanies it. The bone is friable, and measures, below the position of the tooth, five and a half inches in depth. Attached to the fossil there is a portion of soft gray rock, part of the matrix in which it has been imbedded. The tooth is perfect and well preserved. It has the same general form and constitution as the corresponding tooth of the American Mastodon, but is considerably smaller. It bears sufficient resemblance to the plaster cast (represented in fig. 14, pl. xxvii., of "The Extinct Mammalian Fauna of Dakota and Nebraska, &c."). of a tooth, the original of which is lost, from a miocene formation of Maryland, to be viewed as pertaining to the same species. This I had named Mastodon obscurus. The crown of the tooth consists of four transverse divisions together with the merest trace of a heel. As in the cast of the Maryland tooth, the inner lobes of the crown of the California tooth are more mammillary, and less angular than in M. Americanus. The outer lobes, likewise as in the Maryland tooth, have better developed offsets fore and aft internally than in the latter, giving rise to a greater degree of obstruction of the transverse valleys of the crown than in the American Mastodon. The fourth division of the crown is proportionately less well developed, in comparison with those in advance, than in the latter, agreeing also in this respect with the Maryland tooth. The outer lobe of this division is formed of a pair of connate mammillary tubercles, as in the latter, but the tubercles are more equally developed. The inner lobe is a single mammillary eminence not more than half the elevation of the outer lobe. In the Maryland tooth, the corresponding lobe resembles the outer one, consisting of a connate pair of tubercles as well developed as in the outer lobe. The heel in the California tooth, as in the Maryland tooth is formed by a short mammillary eminence occupying the angular space posteriorly of the lobes of the fourth division of the crown. A basal ridge is better developed externally in the California than in the Maryland tooth. Comparative measurements of the California tooth, with the cast of the Maryland tooth, and one of the Mastodon Americanus are as follows: It is not improbable that the California tooth may have pertained to the same species as the fragment of tusk previously noticed, and, perhaps these, together with the Maryland tooth, and others previously referred to Mastodon obscurus, may likewise belong to the same animal. The positive determination of this question must be left for the discovery of additional material to throw light on the relationship of the different specimens which have been thus far presented to our notice. 2. On the cause of the Motion of Glaciers; by J. CROLL, of the Geol. Survey of Scotland, (Phil. Mag., Sept., 1870).-Mr. Croll closes his article on the cause of the motion of glaciers with the following-on the present state of the question, and on the alleged limit to the thickness of a glacier. * Partially estimated, as the specimen is imperfect at its fore part. AM. JOUR. SCI.-THIRD SERIES, VOL. I, No. 1.—JAN., 1871. |