racter given of the lower parts of its course, both in size and respecting its velocity, and resistance of the tide. About 140 miles from Point Padron the width of the river becomes narrow, and is from 3 to 500 yards broad, and continues so to Inga, about 40 miles up, the banks between which the water is hemmed in are, for the whole of this distance, every where precipitous, and composed entirely of masses of slate, which, in several places, run in ledges across from one bank to the other, forming rapids or cataracts, which the natives distinguish by the name of Yellala. The lowest and most formidable of these barriers, was found to be a descending bed of mica slate, whose fall was about 30 feet perpendicular, in a slope of 300 yards. Though in this low state of the river it was scarcely deserving the name of a cataract, it was stated by the natives to make a tremendous noise in the rainy season, and to throw into the air large volumes of white foam; but beyond this again, the river was found to expand to the width of 2, 3, and even more than 4 miles, and to flow with a current of 2 or 3 miles an hour; and near the place where Capt. Tuckey was compelled to abandon the farther prosecution of the journey, (which was about 100 miles beyond Inga, or 280 miles from Cape Padron) it is stated the river put on a majestic appearance, that the scenery was beautiful, and not inferior to that of the banks of the Thames; and the natives of this part all agreed in stating that they know of no impediment to the continued navigation of the river; that the only obstruction in the north-eastern branch was a single ledge of rocks forming a kind of rapid, over which, however, canoes were able to pass. The opinion which existed before the expedition, that the Zaire was in a state of constant flood, or continued to be swelled more or less by freshes during the whole year, has been completely refuted by the present expedition; but Mr. Barrow conceives, that the argument which was founded on this supposition, of its origin being in northern Africa, so far from being weakened, has acquired additional strength from the correction of the error. Mr. Barrow's proposition is, that the Niger connects itself VOL. V. M 1 with the Zaire, by means of the lakes of Wangara. We have not space to follow his arguments on this head, which we think are urged with great ingenuity: but perhaps the whole style of the book, as far as regards the labour of the Editor, is a little too polemical, and more resembling that we have been used to observe in a popular Journal, than what would have been expected from the Secretary of the Admiralty, in his official capacity. We shall close our very imperfect account, by observing that Mr. Burrow is supported in his theory, by a note in Capt. Tucky's Journal, nearly the last he made, in which hs says, "extraordinary quiet rise of the river shews it to issue from some lake, which had received almost the whole of its waters from the north of the line." this, in the same Journal, the words "hypothesis confirmed," occurs; and in a private letter written at Yellala, he dwells more particularly on this proposition. And after ART. XVIII. Remarks on Dr. Ure's " Experiments to determine the Constitution of Liquid Nitric Acid," &c. By Richard Phillips, Esq. F. L. S. & M. Geol. Soc, DR. Ure has asserted, in his observations upon the composition of nitric acid, that "the exact proportion of its two constituents, azote and oxygen, is a problem which seems hitherto to have baffled the best directed efforts of modern science. M. Gay Lussac states, as its composition in 100 parts, 30.4 azote + 69.6 oxygen; and Mr. Dalton 26.7 azote + 73.3 oxygen. Thus discordant are the latest determinations." To which Dr. Ure adds, "I hope soon to be able to present to the public some researches, which may possibly tend to clear up this mystery." I propose to examine the accuracy of Dr. Ure's opinion on this subject, by collecting and comparing the statements which have been recently made with respect to the acid in question, by philosophers of the highest reputation. The first to whom I shall refer, is Sir H. Davy, who observes in p. 265 of his * Journal of Science and the Arts, vol. iv. p. 291. Elements of Chemical Philosophy, "101 will be the number for the acid contained in the pale acid, and in the salts called nitrates, and it will consist of one [proportion] of azote, and five [proportions] of oxygene." Now as Sir H. Davy represents a proportion of azote by 26, and one of oxygen by 15, nitric acid must be composed of 25.742 azote 74.258 oxygen 100.000 The evidence which I shall next adduce as to the composition of nitric acid, is that stated by Dr. Wollaston, in his memoir on Chemical Equivalents. Alluding to some experiments which he had just described, Dr. Wollaston says, "I have no hesitation in prefering the estimate to be obtained from Richter's analysis of nitrate of potash, which gives 67,45, from which if we subtract one portion of azote 17,54, there remain 49.91, so nearly 5 portions of oxygen; that I consider the truth to be 17.54 [azote] + 50 [oxygen], or 67.54." If then 67.54 of nitric acid contain 17.54 of azote, 100 parts must consist of 25.97 azote 100.00 To these determinations I shall add that of M. Gay Lussac, who is indeed quoted by Dr. Ure, to prove that discordance, rather than agreement exists on this subject; if, however, Dr. Ure had extended his researches for evidence sufficiently, he would have seen that this profound chemist, with candour worthy of imitation, has acknowledged the inaccuracy of that analysis, which Dr. Ure erroneously supposes to be, and quotes as, the result of his latest experiments. In the Annales de Chimie et de Physique, (tome i. p. 404.) M. Gay Lussac states nitric acid to be composed of 100 volumes of azote + 250 of oxygen; we have then merely to ascertain the comparative densities of these gases to determine their relative weights. According to Biot and Arago, equal volumes of azote and oxygen are to each other in weight as 0.96913 to 1.10359; therefore a compound of 100 volumes of azote and 250 of oxygen consists of 25.995 azote. 74.005 100.000 These numbers, it will be observed, are nearly identical with those which I have copied from Dr. Wollaston's memoir; they differ immaterially from those given by Sir H. Davy, and do not vary much from Mr. Dalton's analysis, as quoted by Dr. Ure. Considering all who have preceded him in this inquiry, as having failed in the accomplishment of their intention, Dr. Ure appears to be very naturally anxious to supply the deficiency he has discovered. It would seem indeed, as if he had completed the investigation with no ordinary degree of celerity, considering the acknowledged difficulty of the subject; for when alluding in a subsequent part of his paper, to the composition of liquid nitric acid, he says, "when we inquire more minutely into the peculiarity attending the above compound of greatest density, we shall find it to consist of 7 atoms of water 79.24, united to 1 atom of dry acid 67.5.” It is scarcely necessary to observe, that the number representing a compound body, cannot be ascertained without a previous knowledge of the proportions of its constituents; and it must be allowed, that Dr. Ure would not represent nitric acid by a number which he knew to be inaccurate; but having denied the correctness of every previous analysis, we are at liberty to conjecture that 67.5, as above quoted, result from the performance of those experiments, before the close of his paper, which he appears only to have contemplated at its commencement. But supposing this to be the case, it is very remarkable that Dr. Ure should not have allowed, that 67.5 is almost precisely the number by which nitric acid is represented on Dr. Wollaston's scale, for he is acquainted with this instrument, and even quotes it on another occasion to prove its inaccuracy in the present instance, therefore, it would have been but candid to have excepted Dr. Wollaston from those whose efforts have been "baffled." The principal intention of Dr. Ure in the paper now under consideration, is to determine the constitution of liquid nitric acid, a subject which he describes as "involved in perhaps still greater obscurity and contradiction," than that of the dry acid. То prove the justness of this observation, Dr. Ure quotes and compares the statements of Sir H. Davy, Kirwan, Dalton, and Dr. Wollaston, and he concludes them all to be erroneous. According to Dr. Ure, 41.7 of carbonate of potash, consisting of 13.094 of carbonic acid + 28.606 potash, require 32.394 of dry nitric acid for their decomposition, and the nitrate of potash resulting weighs 61 grains: this determination agrees very nearly with Dr. Wollaston's scale, by which it appears that 41.7 of carbonate of potash, consisting of 13.26 carbonic acid + 28.44 potash are decomposed and converted into 60.94 nitrate of potash, by 03.5 of dry nitric acid; and as Dr. Ure considers that 32.394 of dry nitric acid are equivalent to 40.64 of liquid acid of sp. gr. 1.5, this acid must consist in 100 parts of 79.71 dry acid, 20.29 water. 100.00 By Dr. Wollaston's scale, liquid nitric acid of sp. gr. 1.5 is constituted of 67.54 one atom of dry acid, + 22.64, or two atoms of water, 100 parts must therefore consist of 74.895 dry acid, 25.105 water. 100.000 It appears then that whilst the composition of nitrate of potash is nearly similar according to these statements, in Dr. |