atomic weights of the above metallic bodies, nothing can be more Junsatisfactory. We are persuaded that his numerical results would be less equivocally obtained, by a collation of the experiments of other chemists with the modern atomic theory, than by any inference from his own researches.

"I found many years ago," says he, "that when 100 parts of iron are oxidized by passing the steam of water over them at a red heat, they combine with 29,7528 parts of oxygen*" But from the experiments of M. Gay Lussac, it is known, that 100 parts of iron oxidized in this way, unite with 37.8 parts of oxygen. So much for the Doctor's experimental precision.

Now for his theoretical profundity. "Hence it would appear that this supposed oxide (of Gay Lussac), is a compound of 1 atom iron +1 atom oxygen gas t."

We cannot devote much time to his second volume. Persons who can find amusement in haphazard experiments and gratuitous inferences may look into his section on uranium, particularly the 4th and 5th pages. M. Arfwedson made some good researches on the combinations of this metal with oxygen, which Dr. Thomson as usual turns to his own account, by slight modifications. "To determine the atom of chromium I dissolved a quantity of chromate of potash in water, and added tartaric acid to the solution. An effervescence took place, and the solution assumed a fine green colour, because the chromic acid was converted into protoxide of chromium. Ammonia being poured into the green coloured liquid, the protoxide of chromium was precipitated. It was collected on a filtre, well washed, and dried in the open air ‡."

Now we affirm that this experiment, from which he deduces the "atomic weight of chromium, was never made, for the result is impossible. Ammonia does not precipitate oxide of chromium from the above green solution in tartaric acid.

-When solutions of chromate of potash and tartaric acid are mixed, there is an immediate formation of bitartrate of potash, which speedily falls down; and if the tartaric acid be in considerable excess, the chromic acid will be decomposed with effervescence. But the oxide in the resulting green liquid is not preci-pitable by ammonia. Yet Dr. Thomson builds upon a pseudo-experiment, one of his usual atomic structures. Ex uno disce omnes. to Our readers must, by this time, be nearly as tired, as we have long been ourselves, of this illusory and fantastic attempt.

He assigns 9 for the atomic weight of crystallized oxalic acid. The number 7.875 first given in the Philos. Trans. for 1822, is undoubtedly more to be depended on, particularly since it has been confirmed by "a chemical friend, of whose accuracy and information I (Dr. Thomson) entertain a very high opinion §."

* Attempt, i. 355.

+Ibid.

Ibid. ii. 51. § Ibid. ii. 103.

It is diverting to see the pertinacious effrontery with which he still refers to his experiments on oxalic acid, after the full exposure of their absurdity, in our review of his system, (6th edition,) and in our remarks on his answer to that review *.

He now sets to work, in his usual way, on the crystalline hydrate, to ascertain, whether or not, oxalic acid contains hydrogen. This point has, however, been determined so fully by the most delicate and decisive experiments, as utterly to supersede Dr. Thomson's tardy intervention.

Dr. Thomson's experiments to ascertain the atomic weight of tartaric acid betray a rudeness in practical chemistry, unaccountable in so old a hand. He describes tartrate of potash, as containing two atoms of water, separable by heat. The anhydrous salt has, according to him, an atomic weight of 14.25, to which 2.25 2 atoms of water being added, the sum 16.5 will be the number of the crystallized salt. 14.25 of the anhydrous salt, corresponding to 16.5 of the crystals, were found by him exactly equivalent to 20.75 of nitrate of lead. "The mother water (of the mixed solutions of these two salts) was tested with nitrate of lead, and tartrate of potash, without being in the least affected by either. Hence it contained no sensible quantity either of tartaric acid or of lead. The whole of these two bodies was contained in the precipitate which had fallen."

His number for tartrate of potash is unquestionably wrong; and, indeed, though it were right, his conclusion would be erroneous. For the mother water (as he elegantly terms the limpid supernatant liquid) contains, under his proportions, both tartaric acid and oxide of lead. Let it be tested with sulphate of soda, and it will become cloudy; with sulphuretted hydrogen, and it will become very black; or with nitrate of lead, and tartrate of lead will fall. Thus the principle of Richter, of whose application our Doctor is so vain, becomes, under his management, quite deceptious.

His determination of the atomic weight of acetic acid is liable to the same objections. He mixes solutions of 8.875 gr. of oxalate of ammonia (its true atomic weight appropriated as usual to himself, from a prior memoir in the Phil. Trans. for 1822) and of 23.625 grains of acetate of lead; and tests the supernatant liquid" by sulphate of soda and muriate of lime." Now we have the pleasure of informing the Regius Professor of Chemistry, that as a test of lead, sulphate of soda is good for very little on the present occasion; and indeed no accurate chemist would trust to it. Acetate of lead and sulphate of soda can co-exist to a very considerable extent in a clear solution; as the youngest tyro may prove, by adding to one portion of the supernatant liquor, muriate

* Quarterly Journal, xi. 155, and iii. 349.

of barytes, and to another portion of the same, sulphuretted hydrogen or prussiate of potash. In the first case, a copious preeipitate of sulphate of barytes will prove the presence of sulphate of soda; in the second, sulphuret, or ferro-prussiate of lead, will fall. In fact, let solutions of sulphate of soda and acetate of lead be mixed in the proportions indicated by Dr. Thomson's atomic weights of these salts, or in the most exact equivalent proportions; a portion of sulphate of lead will fall, and a corresponding portion of acetate of soda will be formed. To the supernatant liquid, (of any atomic proportion,) add carbonate of soda, and carbonate of lead will be separated in abundance.? When the alkali ceases to act, let a current of sulphuretted hydrogen be passed through the supernatant liquid, and sulphuret of lead will appear. Thus also ferro-prussiate of potash will detect lead in a solution, when the proportion is too minute for the carbonate of soda test.

Dr. Thomson, from his unaccountable ignorance of these gra dations of affinity, has given, as experimental results, quantities which it was impossible to obtain by the method of precipitations. And, hence, had they not been rendered conformable to the researches of Berzelius and other accurate chemists, as well as to the theory of equivalents, the odds would have been ten to one against Dr. Thomson's numbers in almost any case.

The above remarks apply strongly to his sections on citric, tartaric and acetic acids. And we are somewhat surprised that he should expect any attention to his experiments on the ultimate analysis of vegetables, in which upwards of nine grains of the above crystalline acids are treated with only 200 grains of peroxide of copper. No certainty of their thorough decomposition," by the oxygen of the ignited oxide, can be ensured; and the result must be destitute of all authority.

We have now adduced ample, even superfluous, evidence, of the strongest negligence or incapacity in the conduct of his researches on the atomic theory. And moreover, the perplexity into which he runs, in considering the partial and erroneous canons of Berzelius, is a decisive proof that his general views are neither clear nor comprehensive. In our Journal for January 1822, page 307, we endeavoured to shew the fallacy of these pretended general laws of Berzelius. This development of ours seems to have fallen under the Doctor's talons in an unhappy hour; for he tortures and disguises it most unmercifully. We request our readers to compare the passage referred to in our Journal, with Dr. Thomson's "few words respecting Berzelius's law," at p. 469, et seq. of his IId. volume.

The style of writing adopted by the doctor, in this new work, ill accords with the lofty panegyrie pronounced by himself, on his literary attainments. I am remarkably concise, though I hope

always clear, and generally energetic." We humbly apprehend, that more obscure, flat, and tautological phraseology, than that of which the present "Attempt" is made up, is not to be found within the precincts of any English book-factory. Its periodic movements are heavy and reluctant like those of a worn-out atmospheric engine.

In a prefatory address to the students of medicine and chemistry in the University of Glasgow, he advertises them, that his "future courses of lectures will be more entertaining and varied." He assures us that his first reason for publishing this book," is the great advantage which medical practitioners will derive from a knowledge of the atomic weights of bodies, and of the weights of the integrant particles of the salts, &c., which they have occasion to employ in their prescriptions. This knowledge will be easily acquired by a perusal of the following pages; and it will enable those who possess it, to avoid some very awkward blunders into which I have observed too many practitioners, even of considerable celebrity, frequently to fall, to the no little inconvenience of their patients t."

Does Dr. Thomson know a physician, celebrated for his medical attainments, in a printed circular, addressed by himself, to the directors of a royal infirmary, who, to the no little inconvenience of his patients, prescribed the fashionable medicine prussic acid, under the form of prussiate of mercury? Fortunately, this virulent poison was rejected by the stomach before it had time to shew the power of an atomic theorist on medical prescription. We may next hear of corrosive sublimate being substituted for muriatic acid; since they have the same relation to each other as the above two bodies.

Of the merit of his work, the Doctor speaks so authoritatively as to set criticism at defiance. Having affirmed that the present publication will be of no little service to all medical men, and medical students, he says; "The tables contained in this work ought to occupy a place in every laboratory, and to lie upon the shop of every druggist, that he may have it in his power to have recourse to them to regulate all his processes."

The fashion of paper roofs having gone out, we think it doubtful whether his pages will have the fortune to lie upon the shop of every or even of any druggist; but there is another shop where a pulverulent drug is retailed, on whose counter his pages may. possibly appear.

Conceit of knowledge prevents its acquisition. Dr. Thomson, having persuaded himself that all his experiments, however illdevised or ill-executed, are of infinite value and perfect preci

Annals of Philosophy for April, 1822, p. 245.
Attempt, i. Preface viii.
Ibid. Preface xiv.

Captain Sabine on the Figure of the Earth.

141

sion, modestly tells us, that Berzelius and Dulong are in error by ith part, while his own results are quite correct; though in reality they are incomparably more inaccurate, when their errors are not veiled by counterbalancing errors in arithmetic.

There are a few passages of his work composed in a better spirit, and rather freer from the arrogance that blinds him. On these we would willingly have bestowed commendation, had the author not forestalled for himself every laudatory form of ex-, pression.

II. An Account of Experiments to determine the Figure of the Earth by means of the Pendulum vibrating Seconds in different Latitudes; and on various other Subjects of Philosophical Inquiry. By Captain Edward Sabine, F.R.S. &c. Printed at the Expense of the Board of Longitude. Murray.

[The following Review of the first part of Captain Sabine's Work, namely of his Experiments on the Figure of the Earth, has been transmitted to us from a Correspondent in the United States. We are glad to perceive that the Works of British Science are so quickly and so justly appreciated on the other side of the Atlantic.]

FROM the time of the first cultivation of science, the size and figure of the earth have been objects of inquiry. To an ignorant and superficial observer, it presents the appearance of an extended plane; to the earliest cultivators of Astronomy, it shewed an evident curvature in the direction of the meridian; and it was not long before a curvature in a transverse direction was also detected by means of a difference in the apparent time of the occurrence of Lunar eclipses in different places: hence the earth was justly inferred to be of a figure nearly spherical. Other observations have confirmed the near approach of this inference to the truth the shape of the section of the shadow in lunar eclipses is always circular; the appearance of great expanses of water is manifestly spherical; ships in departing from the shore are hidden by the curvature of the earth, long before distance alone could render them invisible; and Humboldt, upon the Peak of Teneriffe, observed an angle of 92° between his visible horizon and the zenith. All these, and innumerable other facts, lead to the confirmation of the received opinion, that the earth is, if not an exact sphere, of a shape that differs but little from that regular geometric solid.

in

Were the earth at rest in space, and had it originally existed a fluid state, its several particles would, by their mutual attraction, have arranged themselves in a spherical form; had the matter of which it is composed been incompressible and homogeneous, this sphere would have been of equal density through