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periment irreproachable, with reference to the determination of carbon in the hydrogen, we should have been obliged to extend indefinitely our absorbing apparatus, and to force the air through the whole apparatus, instead of sucking it through, as in the experiments above described. The object in view was not worth such trouble and expense, and we moreover had not the necessary appliances, so that we were reluctantly forced to give up the inquiry.

Our interest in the subject has been awakened anew by some experiments recently published by H. Karsten,* upon the oxidation of dry non-nitrogenous organic substances by the action of atmospheric air at ordinary temperatures. The method upon which Karsten chiefly relied in these experiments was, in its essential features, identical with the one employed by ourselves, but the difficulty, to which we have referred, of removing carbonic acid from the air employed by any common absorption apparatus, is altogether ignored by him; † as will appear from the following description of his apparatus, quoted from page 349 of his article: "In order to purify from carbonic acid and water the air which I allowed to flow in a slow, continuous stream over the organic substances, I placed before the vessel which contained them chloride of calcium tubes several feet in length, and in front of these a tube containing dry caustic potash, preceded by a bulbtube filled with concentrated solution of caustic potash; by this solution the air was first washed and freed from carbonic acid; it was then led slowly over the dry caustic potash and through the long chloride of calcium tubes, before it came in contact with the organic substances, which had been dried in the water-bath." It is evident, at all events, that this apparatus was far less adequate than our own for the difficult operation of removing carbonic acid from the air.

We do not in the least seek to deny the truth of Karsten's assertion, that carbonic acid is really formed by the action of air at ordinary temperatures upon the substances in question. The fact is not only probable a priori, but would seem to be proved by his incidental statement (p. 348), that carbonic acid was formed when these compounds (sugar, cork, &c.) were exposed during some months to the action of air or oxygen in tubes sealed with mercury in the pneu

*Poggendorff's Ann. der Phys. u. Ch., 1860, CIX. 346.

The reader of Karsten's memoir will observe that, like ourselves, he obtained for the most part only crystalline carbonate of lime, no immediate cloudiness.

matic trough.

In so far as charcoal is concerned, De Saussure * has long ago shown the extreme probability that it is oxidized by the air, even when dry, as it is when wet. Neither do we wish to assert that it is impossible to deprive air of every atom of its carbonic acid. We insist only upon the facts, that it is a matter of no inconsiderable difficulty to do this, that Karsten's apparatus was entirely inadequate, and that nothing in his paper would indicate that he has allowed for this source of error.

It should be distinctly borne in mind, that in the experiments of Karsten, as well as in our own, the question raised is not at all whether the amount of carbonic acid which escapes absorption can be estimated with the balance; for so long as the experiments are qualitative only, and conclusions are based upon the precipitate which is formed in lime-water, it is clearly necessary to remove every trace of carbonic acid from the air employed, no matter how "imponderable" this trace may be. We do not believe that the carbonic acid which escapes absorption in ordinary experiments can be of sufficient amount to be mentioned as a source of inaccuracy in the determination of the carbonic acid of the air, by the method which has been used by so many eminent chemists; for the extent of the error thus introduced must be far less than that of several others to which the absorption process, as commonly employed, is exposed, and which have been pointed out by Hlaziwetz, and in part also by the brothers Rogers. ‡

So far as we know, those observers who have previously touched upon this subject have been occupied with quantitative considerations only. They have, therefore, very properly rested content, when by experiment they have satisfied themselves that the last potash-tube of their series no longer increased in weight during the space of time occupied by a single experiment. § It must, however, be evident to any one who will perform the experiment, that the presence of an amount of carbonic acid which could not be detected by any weighing of potash-tubes may readily be made manifest by precipitating it as crystallized carbonate of lime. In this connection it should be men

* Gilbert's Ann. der Phys., 1814, XLVII. 119, note.

↑ Wiener Akad. Bericht, 1856, XX. 189.

Am. J. Sci., 1848, [2.] V. 115; Edin. New Phil. Journ., XLIV. 150.

Compare, for example, Dumas and Stass, Sur la véritable Poids atomique du Carbone, Ann. Ch. et Phys., [3.] I. 18.

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tioned that Brunner* has distinctly called attention to the extreme difficulty of completely absorbing carbonic acid from the air. Brunner could accomplish this neither by means of a solution of baryta, nor by a mixed solution of chloride of barium and caustic ammonia,† by bits of sponge moistened with baryta or lime-water, nor even by fragments of caustic potash, or asbestos moistened with a solution of potash; he finally chose slightly moistened hydrate of lime, as the best absorbent, and maintains that his method of determining carbonic acid in the air, by this means, is sufficiently accurate for all ordinary

cases.

Professor G. P. Bond presented a memoir on the Light of the Moon and of the Planet Jupiter, containing the results of photographic and optical experiments upon the light of these two bodies.

The rays from Jupiter have been found to possess a remarkable degree of chemical energy compared with those reflected from ordinary opaque substances on the earth, and from the Moon; a similar excess

* Poggendorff's Ann. der Phys. u. Ch., 1832, XXIV. 571.

Having had repeated opportunities of observing the great difficulty - not to say impossibility — of absorbing carbonic acid from mixed gases, especially if these contain so much as one or two per cent of it, by means of these and similar liquids, I am glad to bear witness to the entire accuracy of this much-neglected

statement. F. H. S.

It is a curious fact, which not only corroborates Brunner's observation, but also suggests a more extended use in the laboratory of his favorite absorbent, that manufacturers of coal-gas find in practice, that carbonic acid, when not present in very abnormal quantity, may be readily removed from the impure gas by passing the latter through several layers of dry hydrate of lime, spread in fine powder upon perforated iron grates or upon shelves of basket-work (“dry-lime purification "); while it is practically impossible to absorb all the carbonic acid from similar gas by the wet system, in which the impure gas is forced through milk of lime contained and agitated in several successive purifiers. Yet with the other chief impurity of coal-gas, sulphuretted hydrogen, the reverse of this is the case, for by means of the wet-lime purification, this substance can, in ordinary cases, be very readily and completely removed with an expenditure of but little lime, while with the dry purification this result is far less easily attained. Moreover, this non-absorption of carbonic acid in the wet-lime purifiers cannot be due to any interference caused by the sulphuretted hydrogen, for it is just as difficult to absorb all the carbonic acid from rosin-gas, which contains no sulphuretted hydrogen, as it is to absorb that in the gas prepared from coal.

exists in the optical brightness of this planet. The chemical albedo of Jupiter, supposing the planet to reflect light after the usual manner of opaque substances, exceeds that of the Moon in the proportion of fourteen to one, the optical, in the proportion of eleven or twelve to one.

The experiments are open to the large uncertainties to which photometric comparisons are ordinarily liable; but, assuming their correctness, and that, as there is good reason to suppose, the proportion of sunlight incident on the Moon which is absorbed at its surface, compared with the amount reflected, is less than the smallest of the abovementioned ratios, it would follow that the planet shines in part by native light, agreeably to the old notion of its phosphorescence. It is difficult to put any other construction upon the experiments, provided that Lambert's theory of the quantity of sunlight reflected to the Earth from a planet is applicable in the case of Jupiter. Perhaps a more acceptable explanation is, to suppose that its surface has the property of returning towards the Sun a disproportionate amount of the whole quantity reflected, taking ordinary opaque substances as a standard.

That this condition obtains with the Moon may be inferred from the fact, that at the full, the margin of its disk is brighter than the central regions, indicating a peculiarity in the constitution of its surface which would be likely to produce an excess of brightness at full moon. It is, moreover, placed beyond question from a consideration of the observed variations of the illuminating power of the different phases of the Moon, of which a detailed account is given in the memoir, showing that the theoretical representations of the intensity of moonlight, in its changes from new to full and vice versa, as investigated by Euler and Lambert, bear no resemblance to the actual variations in the amounts transmitted to us. As Jupiter always presents a nearly full phase to the Earth, a similar property of reflection in its surface would tend to explain the anomaly. There is, however, this objection to that hypothesis: while the superior marginal brightness of the full Moon, whatever may be its cause, would naturally lead us to anticipate just that deviation from Lambert's theory of the amount of illumination derived from it which is actually observed to occur, the reverse order in the distribution of light over the disk of Jupiter, namely, its regular increase from the margin to the centre, in very good accordance with the same theory, is a strong argument for adopt

ing the latter as properly applicable to the planet; in which case the explanation suggested would no longer be admissible.

According to the observations communicated, the light of Jupiter, seen from the Earth at its mean opposition, is to the light of the mean full moon as 1 : 6430. Compared with the light of Venus at its greatest brightness, it is as 1 : 4.864.

Professor Bond also read a memoir on the relative brightness of sunlight and moonlight.

Of the results given by Bouguer and Wollaston, for the proportion between sunlight and the light of the full Moon, viz. :

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the preference has been generally given to the latter. Reasons are adduced in the present communication for considering Bouguer's method of observation to be the best of the two, and his results deserving of most confidence. Comparisons, by means of Bengola lights, of the images of the Sun and Moon reflected from a silvered globe, give the value,

s = 471,000.

Other methods, less reliable, also tend to confirm Bouguer's determination.

Professor Bond also communicated a Catalogue of Stars near the Zenith of the Observatory of Harvard College, collected from the best existing authorities, having for its object to furnish to astronomical surveyors in the region of the Great Lakes and elsewhere, nearly in the same parallel, accurate star-positions for the determination of latitude by the zenith telescope.

Professor Agassiz discoursed upon the application of his principles of classification to the systematic arrangement of Polyps.

Professor Cooke, announcing the favorable result of his recent personal application, in behalf of the Academy, to the Royal. Astronomical Society, the Geological Society, and the Museum of Practical Geology, London, to supply deficiencies

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