A MODE OF PROCURING CARBONIC ACID GAS, WITHOUT THE AID OF THE PNEUMATIC TROUGH.

CARBONIC acid gas, which is usually obtained by the aid of a pneumatic trough, and the use of mercury, may be procured, so as to be subjected to experiment, by the following means:-Take a long glass tube, bent at right angles, C, connect it with the three-necked bottle, A, and insert the other end in the jar, D, till it reaches near the bottom. This jar must be perfectly dry, and placed with its mouth upwards. Put pounded marble and muriatic acid into the bottle, F; the muriatic acid combines with the lime, which is one of the constituents of the marble, and sets at liberty the carbonic acid, which is the other constituent, and which, rising in gas, and passing into the jar, D, will, from being heavier than the atmospheric air, expel it and take its place. After a short period, the bottle will be filled with carbonic acid gas. If a lighted candle is then let down into this gas, it will be instantly extinguished. As amusing experiment, another jar may then be taken, rather smaller than the first; place in the bottom of it a lighted taper, and pour the contents of D into this jar, (taking

an

care first of all to remove the tube, C, and to separate the bottle, A,) in the manner water is poured, and the taper will be immediately extinguished. That carbonic acid gas is heavier than common air may be shown by placing a large funnel of paper in a scale with something to counterbalance its weight in the other; then pour into the funnel the air from the jar, D, and the descent of the balance will show this gas is heavier than the atmospheric air. To show that carbonic acid gas is absorbed by water, fill a bottle or jar with this gas, and let it stand over water for some hours; an absorption will gradually take place, till at last none of the gas remains; and this absorption may be made more rapid by agitating the water. Water thus exposed to the action of carbonic acid gas, may be made to absorb rather more than its own bulk, and when thus saturated, it acquires a brisk and pleasant taste. If a forcing-pump be used, a still larger quantity of this gas may be made to combine with the water; and to preserve it, the water must be enclosed in strong stone bottles, and well corked. It is the presence of this gas which gives the sparkling appearance and briskness to champaign, cider, perry, soda water, and other liquids. They are brisk in proportion as the quantity of carbonic acid gas combined with them is great; and as this gas is a product of fermentation, they will also be flat and insipid if that has wholly ceased before they are bottled for preservation.

TRANSACTIONS OF THE CAM

BRIDGE PHILOSOPHICAL SO-
CIETY.

We are happy to hear that "Cam-' bridge is decidedly in an improving. state;" though this testimony is borne to its merits by a Review, every writer in which is a Graduate of that University. Less impartial evidence might have raised some doubts of the assertion, particularly when accompanied by such a proof as is contained in the Transactions of the Cambridge

angles. The upright tubes are tubes of safety, and the use of them, which we believe we omitted to explain in our last Number, is to guard against that reflux of fluid which might happen from a partial vacuum arising from condensation in any of the bottles; for as the air is expelled at the beginning of the operation, and its place supplied by vapour which is liable to condense, the consequence is, when any condensation takes place, the water being more pressed on by the atmospheric air without than by the gas within, passes backwards from one bottle to another, by rising through the tubes, as from D to C, and from C to B, and the different portions are mingled together. The tubes of safety prevent this; for if any such partial vacuum takes place, the atmospheric air is forced through the small quantity of liquid in which they are immersed, and rising into the bottles, preserves the equilibrium. One defect of this apparatus is, that we cannot have the advantage of immersing the tube which comes from A, into the liquid in B; for as it is destined to collect the condensable product, and ought therefore to be without water, it can have no tube of safety; and hence, if the tube issuing from it dip into the liquid in the second, whenever condensation happens, from the gas ceasing to be produced, the liquid will pass backwards into it. To obviate this, what is called the tube of safety of Welther was adopted. It is represented in Fig. 2. It consists of a bent tube, with an additional curvature and a spherical ball. Into this a small quantity of water is put, so as to rise, when the pressure without and within is equal, about half way into the ball. If the elasticity is increased in the internal part of the apparatus, by the production of gas during the distillation, the water is pressed upwards to the funnel at the top; if there is a condensation, it is forced by the atmospheric pressure into the ball; but whenever it has passed the curva

ture beneath the ball, it is obvious that a portion of air must rise through it, and will pass into the globe or bottle to the tube of which it is adapted, and preserve the equilibrium. This tube is inconvenient in its form, liable to be broken, and does not admit of great pressure. But with this improvement the apparatus now described is not so safe, nor so serviceable as the adaptation of this apparatus described in our last Number.

ANALYSIS OF SCIENTIFIC JOURNALS.

ANNALS OF PHILOSOPHY FOR APRIL 1824.

(Continued from p. 37.)

THERE is a great proportion of original Articles in the Annals for this month, which continues to sustain its reputation. Article I. is a communication by a Mr. Crichton, of Glasgow," On Expansions, particularly on those of Glass and Mercury." These two substances being used to make almost all the instruments by which we measure the expansive powers of other bodies, it is of the highest importance, as far as regards scientific research, that their expansive power should be most accurately determined. Accordingly, experiments for this purpose have been made at various times by very celebrated mathematicians and Chemists, such as Roy, Smeaton, Deluc, Lavoisier, and La Place; and particularly by Messrs. Dulong and Petit, in 1818, whose memoir on this subject obtained a prize. Mr. Crichton's observations are particularly directed to the experiments of the latter gentleman. The mode those gentlemen took to ascertain the expansive power of mercury, was to notice what quantity of it was expelled by subject, ing it to the boiling temperature in glass vessels; but in these calculations, according to Mr. Crichton, they omitted to take into account the degree in which the glass itself expanded during the experiment.-"To learn the true dilatation," says Mr. Crichton, “ we have only

to recollect, that whatever quantity is expelled from a vessel by a given increase of temperature, something more would be expelled if the vessel itself did not expand; and this supposed portion must be added to the quantity expelled at the higher temperature, (as found by experiment,) and deducted from that then remaining in the vessel, that each may represent what it would be if the vessel were not liable to expansion." Mr. Crichton then gives a concise general algebraic formula, for the estimation of this dilatation in all vessels; but, concise though it be, we must decline inserting it here on account of its length.

Art. II. is by Dr. Thomas Thomson, and contains a corrected expression for the "Atomic Weight of Boracic and Tartaric Acids." We confess we do not see the utility of, or the real knowledge gained by ascribing to one body a certain proportionate property in relation to some other body, which is quite unknown. What should we think of a geographer who should pretend to instruct his pupils by telling them Paris was four times as far from London as Dover, and Rome fourteen times, if neither the geographer nor the pupils knew, nor could possibly know, what distance Dover was from London? Would not this be darkening knowledge by words, pretending to explain that which was unknown by some other thing equally unknown? The persons who, with such an amusing gravity, go about calculating the comparative weight of atoms, the very existence of which is unknown, must either have a very strange idea of what knowledge consists in, or a very strong propensity to detect barmony in apparent proportions. We shall pass by the Atomic Weight of Boracic and Tartaric Acids, with merely saying, that according to Dr. Thomson's corrected account, the weight of the former is represented by 3.0, and of the latter by 8.25. We have less even to say of Art. III., which is a Table of "Corrections in Right Ascension of 37

Stars;" those who want to consult it must necessarily have recourse to the Annals.

Art. IV. is "A contribution to a more accurate knowledge of Uranium," by I. A. Arfwedson. Translated from the Transactions of the Swedish Royal Society. First, Mr. Arfwedson says that the oxide of this metal, which had been operated on by preceding Chemists, was probably not pure; and then he shows

HOW THE PROTOXIDE OF URANIUM MAY BE OBTAINED IN A STATE OF COMPLETE PURITY.

Finely pulverized pechblende is dissolved, by means of a gentle heat, in a mixture of nitric and muriatic acids. When the decomposition of the mineral is completed, and most of the acid expelled, a little muriatic acid is to be added, after which the liquid is to be diluted with a good deal of water. The sulphur, silica, and a portion of the gangue remain finally undissolved. A current of sulphuretted hydrogen gas must now be passed through the liquid as long as any precipitate falls, which is at first dark brown, consisting of sulphurets of copper, arsenic, and lead; and last becomes yellow, consisting of sulphuret of arsenic. Let the liquid be filtered and digested with a little additional nitric acid, to peroxidise the iron which remains. By this process the liquid is changed from light green to yellow. Carbonate of ammonia · now added in excess takes up the oxides of uranium, of cobalt, and of zinc, but leaves oxide of iron undissolved. Should the solution contain a portion of earth, it will be separated with the oxide of iron. The filtered solution is then boiled as long as carbonate of ammonia is disengaged. A portion of the oxide of cobalt remains in the solution, which acquires a faintish reddish colour, but another portion of it is precipitated along with the oxide of uranium and the zinc. The precipitate is collected on the filter, washed and dried. It is then heated to redness, by which it changes from yellow to dark green;