and other fluids, are in direct contradiction of his own theory, as is also the extinction of the light of these mixtures by the application of a high degree of heat.

If the light emitted by animals were derived from their food, or the air they respire, as supposed by CARRADORI, the phenomenon should be increased or diminished, according to the quantity of food or air, that the creatures consume; but we do not find this to be the case; for in those situations where they are sometimes found to be most luminous, they are deprived, in a great measure, of these assumed sources of their light.

In fact, the luminous exhibitions of living animals are not only independent of all foreign light, but are frequently des troyed by the latter. I have always found the shining of the medusa to cease upon the rising of the moon, or at the approach of day; and when out of the sea, I never could excite them to throw out light until they had been kept for some time in the dark; all the luminous insects likewise secrete themselves as much as possible during the day time, and go abroad only at night. I have, it is true, found that the scolopendra electrica will not shine unless it has been previously exposed to solar light; but I have observed that it shone as brilliantly and as frequently, after being kept a short time in a light situation, as when left unrecovered the whole day. The circumstance of the scolopendra requiring exposure previous to its giving out light, is very unaccountable, as the insect, when left to itself, always seeks as much as possible concealment during the day; indeed it is the opinion of some naturalists that it is killed by the light of the sun.

The opinions of Brugnatelli and Carradori are connected with some general doctrines, respecting the nature_of light, which I shall not at present venture to discuss. It appears to me, that the question is still unresolved, whether light has a substantial existence, or is a phenomenon depending upon certain operations or conditions of the ordinary forms of matter. But the highly ingenious researches of Count Rumford, on the laws of what had been called subtile fluids, and the extraordinary advances lately made by Mr. Davy, on the decomposition of substances, that were hitherto looked upon as elementary, give us reason to hope, that future investigations may unfold views of the material world, of which we can at present have only an indistinct conception; that new modes of analysis may enable us to see things, not "through a glass darkly," but more nearly as they are; and that the boundaries of physical and metaphysical science, now so far asunder, may be made to approach each other.

In the present state of our knowledge, our business should

be

be, to collect, arrange, and compare phenomena, rather than to speculate upon their nature. Nevertheless, I cannot refrain from observing, that the circumstances attending the luminous appearance of living animals, are much more favourable to the supposition of light being a property, than a substance. The quantity of light emitted by an animal in a certain time, (admitting it to be matter) far exceeds that which could be possibly supplied by the sources, from whence it is usually supposed to be derived. Thus the luminous appearance of some medusæ may be continued with the intermission of short intervals for an indefinite time, notwithstanding the creature be kept in darkness, and without any other food than what a small quantity of filtered sea water would afford. The uninterrupted and long continued light that is sometimes evolved by the luminous sacs, and the ova of the glow-worm, is also inconsistent with the notion of an accumulation and subsequent dispersion of a material substance.

I shall terminate this paper by an enumeration of the several conclusions, that are the result of the observations I have been able to make upon the phenomena of animal light. The property of emitting light is confined to animals of the simplest organization, the greater number of which are inhabitants of the sea. The luminous property is not constant, but in general, exists only at certain periods, and in particular states of the animal's body.-The power of shewing light resides in a peculiar substance or fluid, which is sometimes situated in a particular organ, and at others diffused throughout the animal's body. The light is differently regulated, when the luminous matter exists in the living body, and when it is abstracted from it. In the first case, it is intermitting, or alternated with periods of darkness; is commonly produced or increased by a muscular effort; and is sometimes absolutely dependant upon the will of the animal. In the second case, the luminous appearance is usually permanent until it becomes extinct, after, which it may be restored directly by friction, concussion, and the application of warmth; which last causes, operate on the luminous matter (while in the living body,) only indirectly, by exciting the animal. The luminous matter, in all situations, so far from possessing phosphoric properties, is combustible, and loses the quality of emitting light, by being dried, or much heated. -The exhibition of light, however long it may be continued, causes no diminution of the bulk of the luminous matter. It does not require the presence of pure air, and is not extinguished by other gasses.

The luminous appearance of living animals is not exhausted

3 U 2

hausted by long continuance, or frequent repetitions, nor accumulated by exposure to natural light; it is therefore, not dependent upon any foreign source, but inheres as a property, in a peculiarly organized animal substance or fluid, and is regulated by the same laws which govern all the other functions of living beings.

The light of the sea is always produced by living animals, and most frequently by the presence of the medusa scintillans. When great numbers of this species approach the surface, they sometimes coalesce together, and cause that snowy or milky appearance of the sea, which is so alarming to navigators. These animals, when congregated on the surface of the water, can produce a flash of light, somewhat like an electric corruscation. When the luminous medusæ are very numerous, as frequently happens in confined bays, they form a considerable portion of the mass of the sea, at which times they render the water heavier, and more nauseous to the taste; it is therefore adviseable to always strain sea water be fore it is drunk.

The lurainous property does not appear to have any con nection with the economy of the animals that possess it, except in the flying insects, which by that means discover each other at night, for the purpose of sexual congress.

On preparing Acetate of Potash, so as to obtain it in a saturated State, and of a White Colour. By Messrs. BERNOULLY and FREMY.

(Annales de Chimie,)

MR. BERNOULLY, of Basil, commenced his memoir

with attempting to discover the colouring matter that is so injurious to the appearance of the salt, and which does not belong either to the potash or the acetic acid, so that it must be a foreign matter contained in common vinegar, and carried over with it in distillation. This principle is less vola tile than acetic acid, as distilled vinegar leaves a residuum on being evaporated. It is not very soluble itself without the assistance of the acid, as it is partly precipitated when the acid is saturated with potash. It is evidently of a vegeto-animal nature, from the odour that it exhales upon a burning coal, and from the prussiate of ammonia that is yielded in the distillation of acetate of potash prepared with distilled vinegar, but which does not occur in the distillation of that prepared with radical vinegar. So that the colouring matter appears to be some remains of the yeast left in common

vinegar,

vinegar, carried over when it is distilled, and more or less altered by this operation.

The acetate of potash may also be discoloured by the empyreumatic oil with which the distilled vinegar becomes charged when the operation is pushed too far. The acci dental sullying arising from the oxyds of iron and of manganese contained in the common alkalies, or from metallic vessels being employed in its preparation, is easily avoided.

In order to get rid of the yeast, it is necessary to choose for distillation clear, very strong, and completely fermented vinegar, and to distill with a very gentle heat, not exceeding that of a gentle boiling heat. If, however, in spite of these precautions, the acetate should not be white, the solution must be gently boiled with well-calcined charcoal previous to evaporation; the operation must be conducted slowly.

The distillation of the vinegar must be stopped the instant that the empyreumatic oil begins to come over: for although the succeeding vinegar may be perfectly white, it becomes coloured during the evaporation, and when this once happens it cannot be remedied.

Mr. Fremy's memoir enters into more details. In crystallising the acetate, it is extremely difficult to separate the crystals from the mother-water; he therefore tried the effects of double decompositions. Acctate of lime treated with carbonate or sulphate of potash afforded a salt of the usual colour. Common acetate of lead and carbonate of soda afforded a salt sufficiently white; but an error in the quantities of the ingredients may be attended with bad consequences. He found that the colour of the acetate proceeds not only from some foreign colouring substance that is contained in the distilled vinegar, but also from the alkali itself when it is in excess, and thus enabled to re-act upon the foreign substance; for on preparing two portions of acetate with the same distiled vinegar, one of which had designedly an excess of acid, and the other of alkali, the latter portion was evidently deeper coloured than the former.

To destroy the colouring matter, he filtered the distilled vinegar upon charcoal, then nearly saturated it with carbonate of potash, and carefully retained an excess of acid during the evaporation, by which means he obtained an acetate as white as if it had been melted.

Although this process is very simple, it is not practicable, because the acetate of potash is mixed with acetate of lime coming from the charcoal, which is prejudicial to the drying. It would be easy to separate the lime, by adding a slight excess of carbonate of potash, afterwards adding an excess of the acid; but it is more simple to saturate the acid

at

at first. The liquor being left upon the charcoal for twenty days, and exposed to the sun's rays, furnished a salt still whiter than before; and Mr. Fermy imagines the same effect may be obtained by exposure to the rays of the sun without the addition of charcoal.

Part of the colouring matter is precipitated during the saturation of the vinegar: it is but slightly soluble in water, but some portion of it remains in the solution of the acetate of potash. When distilled vinegar has been filtrated upon very pure charcoal, such as that from sugarcandy, the same precipitate is not obtained as before the filtration.

Two hecatogrammes (6 oz.) of excellent acetic ether were obtained by rectifying the first produce of the distillation of 70 litres (quarts) of distilled vinegar upon potash.

The discoloration of the acetate by exposing it to the solar rays, did not succeed when tried by the Committee to whom the two preceding memoirs were referred.

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

IT

(Nichol. Jour.)

T has been said, that in calm summer evenings the dictam, nus albus evolves hydrogen gas, or a highly odorous inflammable effluvium, which explodes when brought into contact with the flame of a candle; an opinion that is maintained in the latest botanical publications I have seen.

When I first became acquainted with the above notion, my curiosity was excited, and I longed for an opportunity 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, the outside of the corolla, and especially the tops of the filaments, 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 weather 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 lightblue coloured flame, which proceeded along the course of the peduncles,