on phosphorua

"Mr. Davy says it is evident, that the method we employ Experiments in our endeavours to show, that his experiments on phospho- and phosphurus and phosphuretted hidrogen are not accurate, do not retted hidro apply to the case he has in contemplation. They have acted,' he adds, "on the phosphuret of potassium with hot water, and thus they form phosphate of potash, and a large quantity of phosphuretted hidrogén gas; whereas, when strong muriatic acid is employed, the muriate of potassium is produced, and the oxigen is furnished solely, or princi pally to the potassium. We cannot form just conclusions, unless when the potassium alone is oxided; and my design in employing but a small quantity of acid was to oxide this substance alone."

"We shall observe, 1st, that we have treated the phosphuret of potassium not with hot water only, but with acids also; and that in every case we have proved, that more phosphuretted hidrogen gas was obtained, than was required to represent the hidrogen gas, that the potassium of this phos phuret was capable of furnishing with water; and that therefore Mr. Davy has nothing to object to the means we No oxigen exhave employed to refute his opinion, or to demonstrate, that ists in them. no oxigen exists either in phosphuretted hidrogen, ör in

phosphorus."

"

excess absorbs hidrogen from

"Mr. Davy accuses us of contradicting ourselves, as we Potassium in have said, Mém. d'Arc., vol. II, p.304, that potassium, when heated in phosphuretted, sulphuretted, or arsenicated hidro- phosphuretted, gen, absorbs the phosphorus, sulphur, or arsenic, and a portion sulph. or ars., hidrogen; of hidrogen; and we say, Jour. de Phys. Dec. 1809, that potassium sets free all the hidrogen of phosphuretted or arsenicated hidrogen. In this there is nothing extraordinary. At first we employed an excess of potassium, and an absorption

of hidrogen took place. But since, particularly when Mr. not otherwise, Davy had concluded from his experiments, that sulphur, phosphorus, and phosphuretted and sulphuretted hidrogen, contain oxigen, hav.ng exa ined anew the action of potas- sium on sulphuretted, phosphuretted, and arsenicated hidrogen gas; and for this having necessarily employed an excess of gas; we have seen, that, in this case, no portion of the hidrogen of the phosphuretted or arsenicated hidrogen is absorbed. Tus it appears, that we are perfectly consistent; VOL. XXIX.-MAY, 1811.

F

since

Potassium ab

sorbs phosph.

hid. gas without flame,

sulph. hid,

with.

Arsenicated hidrogen contains oxigen.

No oxigen in sulphur or phosphorus.

Collection of
Experiments.

since we can at pleasure cause the hidrogen of these gasses to be absorbed or not by the potassium.

"Mr. Davy observes, that we have said potassium absorbs phosphuretted hidrogen gas with flame; while on the ⚫ contrary, as he has found, it absorbs it without flame. This is true, and the mistake has even occasioned us to make another, which Mr. Davy does not mention; it has led us to say, that potassium absorbs sulphuretted hidrogen gas without the emission of light. The fact is, these two experiments were made at the same time, and one was written down for the other. This may easily be conceived, for the phenomena are too visible not to be perceived. If we give this explanation however, it is not to exculpate ourselves from the mistake,"

"Mr. Davy complains of our having said, that, if he were acquainted with the action of arsenicated hidrogen gas on potassium, he would have inferred from it the existence - of oxigen in this gas. We think the same still, because we do not obtain, on treating arsenic with water, a quantity of hidrogen gas representing that which potassium is capable of giving with water.

"Mr. Davy could have wished, that we had spoken of his experiments to demonstrate the existence of hidrogen in sulphur and phosphorus; and complains, that we have only endeavoured to point out errours. But our only object was to inquire, whether these experiments demonstrated the existence of oxigen in these two substances: and, as no one of them proves this, and as the result of all are contrary to ours, we could not but draw inferences from them opposite to those of Mr. Davy."

"In a Collection of our Experiments, now in the press, we shall answer all Mr. Davy's objections, and endeavour to render him the completest justice."

X.

Observations respecting the Sensible Perspiration of the Dictamnus Albus, or Fraxinella. By Mr. ROBERT Lyall, Surgeon, M. R. P. S. E.&c. Communicated by the Author.

Assertion that IT has been said, that in calm summer evenings the the bastard dit dictamnus albus evolves hidrogen gas, or a highly odorous inflammable

inflammable

inflammable effluvium, which explodes when brought into any emits an contact with the flame of a candle; an opinion that is main- gas. tained in the latest botanical publications I have seen.

When I first became acquainted with the above notion, Experiment my curiosity was excited, and I longed for an opportunity made on it. to make the experiment, which was not very long denied me. The result of my observations I shall now relate in order,

that the subject may be more accurately investigated.

I need scarcely premise, that the peduncles, the calyx, Glands on it the outside of the corolla, and especially the tops of the fi- containing a fluid. laments, and the germen of the dictamnus, are covered with glands of an oblong form, many of them supported on little pedicles, all of them of a beautiful red colour, and containing a somewhat viscid fluid.

On the 10th of July, about ten in the evening, the wea- Exp. 1, ther fine, and the temperature 66, I commenced my experiments on the dictamnus. By holding a lighted candle at the bottom of a raceme of flowers, inconsiderable explosions, or rather a hissing noise was occasioned, accompanied by light-blue coloured flame, which proceeded along the course of the peduncles, &c., and ascended even higher than the top of the stem; a good deal resembling an amusing experiment sometimes practised in the theatre, and often by boys, by means of powdered resin and a burning candle, &c. Immediately after the combustion, the surrounding atmosphere became tainted with odoriferous effluvia, exactly similar to what the healthy flowers, though much stronger, emit. July 13, I repeated this experiment, at the same Exp. 2: hour as before. The evening was fine, but the plants were wet with the afternoon's rain. Scarcely any noise was produced; the experiment not succeeding as before.

At another time I brought home a raceme of flowers, Other experi and after it had stood with its end placed in water for ments. two hours, I approached a burning candle to it, and little explosions followed. I replaced the raceme in the water, and next morning darkened my room, and made the same experiment, but heard no explosions. Since the 13th of July, I have frequently repeated the first experiment, but never have succeeded nearly so well as at first; a little hiss ing noise, attended with a small flame, only occurring now F* and

The glands destroyed in these experi

ments.

and no smell of hidrogen everperceived.

and then, occasioned in consequence of the bursting, I imagine, of the glands of new flowers; which, from their not being before developed, remained uninjured, during former experiments.

On examining the plants after the combustion, I observed, that the glands were completely destroyed; and thus I was led to suppose, that the resinous fluid which they contained was burnt during the explosion; and not that hidrogen, or any inflammable vapour was exhaled. Since afterexperiments never succeeded so well as the first; and because the smell of hidrogen was never present, either before or after the experiment, I think I am strengthened in my opinion. At the same time, however, I confess, that I am not completely satisfied with my own observations, and therefore wish that some one, who has convenience, would not only repeat the experiments, but communicate the result of them to the public, and thus either ascertain the truth of what I have reported, or annul it altogether.

Different

means em.

XI.

Description and Use of a Rheumameter, to estimate and compare the Velocity of the Current of Rivers; by Mr. REGNIER, Conservator of the central Museum of Artillery.

FROM Mariotte to the present day men of the first emi

ployed to mea. hence have employed different means to estimate the velosure the velocity and force of rivers; and their methods, more or less city of rivers. ingenious, seem to leave nothing to be desired. I may incur

applied to this

the imputation of temerity therefore in bringing forward another, perhaps not equally good; but as it is very simple, attended with little expense, and requires no calculation, it may suit a great many persons, who are desirous of erecting mills or other works on rivers, with the velocity of which they are unacquainted.

Dynamometer Mr. Gauthey, inspector general of bridges and highways, purpose, first employed my spring powderproof in the shape of a

Abridged from Sonnini's Biblioth. Physico-écon. March, 1810, p. 193.

steelyard,

steelyard, to ascertain the force of a stream on a given sur face. His process is analogous to that of the bent lever balance, as described by Michelotti in his work on Experimental Hydraulics; but his method is not so simple, nor his apparatus so cheap and portable, as that of Mr. Gauthier.

I have observed however, that the hand which holds the Improvem ent in its applica rod, to which the instrument is fixed, is liable unintention- tion, ally to give it an additional impulse. This inconvenience has led me to employ the steelyard in a different manner, which appears to me more convenient and more accurate, and affords the double advantage of measuring in distinct manners both the velocity of the current, and its absolute force on a given surface, so that the two modes of examination mutually check each other.

scribed.

The apparatus consists of a cork log, or float, 10 cent. Apparatus de [4 inches] square, in the shape of a cube, so ballasted as just to sink to the level of the surface. A small reel, turning very freely, on which is wound a silk cord of a given length, to measure the distance the log should float. A small dynamometer, resembling that I constructed to measure the strength of threads of silk, cotton, or flax. With this apparatus, which may be carried in the pocket, the action of a current may easily be ascertained.

To the upper part of the log is fastened a silk cord, forming an acute angle, like the string of a kite; and to the point of the angle is hooked a red string two yards long, tied to a green string ten yards long, which is entirely rolled up on the reel. The other end of the green string is fastened to the reel, which the observer holds in his hand. A cord of two colours is used, to distinguish the part in tended to measure the distance passed through from that which should be in the water with the log.

I have preferred a silk to a hempen cord, not only be cause silk is stronger and more pliable, but because it does not twist in the water, and retard the progress of the log. To satisfy myself of this, I have thrown into the water little pellets of paper, which floated freely by the side of the log, and the eye could perceive a sufficient uniformity in a distance of ten yards, the measure fixed on.

To