Chapter IV: Book 5: , chap. 2, Page 403—Account of a new compound Microscope for (3)

The next section comprises “the compounds of the simple [p066] non-metallic acidifiable combustibles with each other.” It includes the important subject of ammonia, of the varieties of carburetted hydrogen, sulphuretted and phosphuretted hydrogen, and cyanogen and its compounds. The metals are then treated of, and to these succeed their salts; and though the execution of this part of the work betrays some haste, it shows also considerable reading, and some originality: the general views are well and clearly sketched, but there are many points upon which we are entirely at variance with our author; and we more especially object to his account of the action of chlorides upon water, and to his notions concerning the “muriates of oxides,” a class of compounds of which, with one or two exceptions, we are disinclined to admit the existence. If common salt be a _chloride_ of _sodium_, and experiment obliges us so to regard it, what is there in its aqueous solution that should lead us to consider it as containing a _muriate_ of _soda_; what evidence of any new arrangement of elements? Dr. T. is certainly in mistake, when he says, “for all practical purposes, therefore, the solution of a metallic chloride in water may be viewed as the muriate of an oxide, and on this account I shall always regard it as such in the present treatise.” This inconsiderate dogma taints much of the reasoning upon the chlorides, &c., and is manifestly culled in the Thomsonian school, though we have indeed heard that a Professor at Edinburgh thus addresses his pupils upon the above subject: “The elaborate researches of the illustrious Davy have taught us that common salt is a binary compound of chlorine and sodium, a chloride, therefore, or a chloruret of sodium. But it is only chloride of sodium whilst quiescent in the salt-cellar; for no sooner does it come into contact with the salivary humidity of the fauces, than, by the play of affinities, which I have elsewhere explained, the sodium becomes soda, and the chlorine generates muriatic acid;—that, therefore, which upon the table is chloride of sodium, is muriate of soda in the mouth; and this again, when desiccated or deprived of humidity, retrogrades into its former state.”

Dr. Turner again falls into error, as we humbly conceive, in calling certain salts, such, for instance, as those of the peroxide of iron, _sesquisalts_, a term properly applied in those cases only where one proportional of a protoxide unites with one and a half of an acid, such for instance as the _sesquicarbonate of soda_, &c., but in the sesquisulphate of iron, one proportional of the peroxide contains 1.5 of oxygen, and [p067] necessarily, therefore, (according to Berzelius’ canon, if the Doctor pleases,) requires 1.5 of acid to convert it into a salt; just as the commonly constituted peroxides (containing two proportionals of oxygen) require two of acid. Dr. Thomson, with all his nomenclatural pretensions, has fallen into the same error.

The part of our author’s work which treats of the chemistry of organic bodies is, upon the whole, an unexceptionable and accurate epitome of that complicated branch of the science. It has its inaccuracies, but they apparently arise out of the difficulty of condensing into the space of a few pages, matter which, as we have elsewhere remarked, would require an ample volume for its extended and perspicuous details.

In our hasty account of this work, we have rather dwelt upon its defects than its merits, in the hope of seeing another and more extended edition, free from what we consider as serious obstacles to the success and usefulness of the present production. We hope that Dr. Turner will not feel offended at the freedom with which our remarks are offered. We are anxious that a writer of such good information should be induced to think for himself; at least, that he should accurately weigh the pretensions, and inquire into the originality of those views and researches upon which he bestows such unqualified and, in our opinion, undeserved praise, and to which he assents with a facility unbecoming one who evidently possesses the means of testing their merits.

_Experiments on Audition_.

[Communicated by Mr. C. Wheatstone.]

The recent valuable experiments of Savart[23] and of Dr. Wollaston have added to our stock of information several important and hitherto unnoticed phenomena relating audition; but, notwithstanding the investigations of these distinguished experimentalists, and though the physiology of the ear has been an object of unceasing attention for many centuries, yet we are far from possessing a perfect knowledge of the functions of the various parts of this organ. The description of new facts illustrative of this subject cannot, therefore, be devoid of interest; [p068] and though I do not anticipate that the observations contained in this communication will lead to any important results, their novelty may claim for them some attention from the readers of your Journal.

§ 1.

If the hand be placed so as to cover the ear, or if the entrance of the meatus auditorius be closed by the finger without pressure, the perception of external sounds will be considerably diminished, but the sounds of the voice produced internally will be greatly augmented: the pronunciation of those vowels in which the cavity of the mouth is the most closed, as _e_ _ou_, &c., produce the strongest effect; on articulating smartly the syllables _te_ and _kew_, the sound will be painfully loud.

Placing the conducting stem of a sounding tuning-fork[24] on any part of the head, when the ears are closed as above described, a similar augmentation of sound will be observed. When one ear remains open, the sound will always be referred to the closed ear, but when both ears are closed, the sound will appear louder in that ear the nearer to which it is produced. If, therefore, the tuning-fork be applied above the temporal bone near either ear, it will be apparently heard by that ear to which it is adjacent; but on removing the hand from this ear (although the fork remains in the same situation) the sound will appear to be referred immediately to the opposite ear.

In the case of the vocal articulations, the augmentation is accompanied by a reedy sound, occasioned by the strong agitations of the tympanum. When the air in the meatus is compressed against this membrane by pressing the hand _close_ to the ear, or when the eustachian tube is exhausted by the means indicated by Dr. Wollaston, the reedy sound is no longer heard, and the augmentation is considerably diminished. The ringing [p069] noise which simultaneously accompanies a very intense sound, proceeds from the same cause, and may be prevented by the same means. This ringing may be produced by applying the stem of a sounding tuning-fork to the hand when covering the ear, or by whistling when a hearing trumpet is placed to the ear. As a proof that the resulting augmentation, which, when great, excites the vibrations of the tympanum, is owing to the reciprocation of the vibrations by the air contained within the closed cavity, it may be mentioned, that when the entrance of the meatus is closed by a fibrous substance, as wool, &c., no increase is obtained.

If the meatus and the concha of one ear be filled with water, the sounds above-mentioned will be referred to the cavity containing the water in the same way as when it contained air, and was closed by the hand; it will be indifferent whether any partition be interposed between the cavity and the external air; as the water is equally well insulated by a surface of air as by a solid body.

§ 2.

The preceding experiments have shown, that sounds immediately communicated to the closed meatus externus are very greatly augmented; and it is an obvious inference, that if _external_ sounds can be communicated, so as to act on the cavity in a similar manner, they must receive a corresponding augmentation. The great intensity with which sound is transmitted by solid rods, at the same time that its diffusion is prevented, affords a ready means of effecting this purpose, and of constructing an instrument, which, from its rendering audible the weakest sounds, may with propriety be named a Microphone.

Procure two flat pieces of plated metal, each sufficiently large to cover the external ear, to the form also of which they may be adapted; on the outside of each plate directly opposite the meatus, rivet a rod of iron or brass wire about 16 inches in length, and one-eighth of an inch in diameter, and fasten the two rods together at their unfixed extremities, so as to meet in a single point. The rods must be so curved, that when the plates are applied to the ears, each rod may at one end be perpendicularly inserted into its corresponding plate, and at the other end may meet before the head in the plane of the mesial [p070] line. The spring of the rods will be sufficient to fix the plates to the ears, but for greater security ribands may be attached to each rod near its insertion in the plate, and be tied behind the head.

A more simple instrument may be constructed to be applied to one ear only, by inserting a straight rod perpendicularly into a similar plate to those described above.

The Microphone is calculated only for hearing sounds when it is in immediate contact with sonorous bodies; when they are diffused by their transmission through the air, this instrument will not afford the slightest assistance.

It is not my intention in this place to detail all the various experiments which may be made with this instrument, a few will suffice to enable the experimenter to vary them at his pleasure.

1. If a bell be rung in a vessel of water, and the point of the microphone be placed in the water at different distances from the bell, the differences of intensity will be very sensible. 2. If the point of the microphone be applied to the sides of a vessel containing a boiling liquid, or if it be placed in the liquid itself, the various sounds which are rendered may be heard very distinctly. 3. The instrument affords a means of ascertaining, with considerable accuracy, the points of a sonorous body at which the intensity of vibration is the greatest or least; thus, placing its point on different parts of the sounding board of a violin or guitar, whilst one of its strings is in vibration, the points of greatest and least vibration are easily distinguished. 4. If the stem of a sounding tuning-fork be brought in contact with any part of the microphone, and at the same time a musical sound be produced by the voice, the most uninitiated ear [p071] will be able to perceive the consonance or dissonance of the two sounds; the roughness of discords, and the beatings of imperfect consonances, are thereby rendered so extremely disagreeable, and form so evident a contrast to the agreeable harmony and smoothness of two perfectly consonant sounds, that it is impossible that they can be confounded.

§ 3.

Apply the broad sides of two sounding tuning-forks, both being unisons, to the same ear; on removing one fork to the opposite ear, allowing the other to remain, the sensation will be considerably augmented.

It is well known, that when two consonant sounds are heard together, a third sound results from the coincidences of their vibrations; and that this third sound, which is called the grave harmonic, is always equal to unity, when the two primitive sounds are represented by the lowest integral numbers. This being premised, select two tuning-forks, the sounds of which differ by any consonant interval excepting the octave; place the broad sides of their branches, while in vibration, close to one ear, in such a manner that they shall nearly touch at the acoustic axis, the resulting grave harmonic will then be strongly audible, combined with the two other sounds; place afterwards one fork to each ear, and the consonance will be heard much richer in volume, but no audible indications whatever of the third sound will be perceived.

§ 4.

Very acute sounds, such as the chirping of the gryllus campestris, &c., are rendered inaudible by exhausting the air from the Eustachian tube, and thereby producing a tension of the membrane of the tympanum; the different thicknesses or tensions of this membrane may therefore occasion that diversity of the limits of audibility, with regard to the acute sounds which Dr. Wollaston has pointed out as existing in different individuals; if so, it would be desirable to ascertain this limit in individuals in whom the tympanum is perforated, or destroyed.

§ 5.

When the auricula is brought forward, all _acute_ sounds are rendered much more intense, but no sensible difference is [p072] perceived with regard to the grave sounds. The _higher_ tones of glass staccados, or of an octave flute, the ticking of a watch, all kinds of sibilant sounds, &c. are thus greatly augmented: the experiment is easily tried, by whistling very shrill notes. A still greater augmentation of the acute sounds is obtained, by placing the hands formed into a concave behind the ears, and by bending downwards the upper part of the auricula, so as to obtain a more complete cavity.

§ 6.

I will conclude with the following observation: I had, in consequence of a cold, a very slight pain in my left ear; on sounding the regular notes of the piano-forte, C^3 and C^4 were much louder than the others, and the loudness was much increased, by placing the hand in the manner above described to the left ear. When it was pressed close, or when the Eustachian tube was closed, the intensities of all the notes were equalized. I attribute this affection to the diminished tension of the membrana tympani, which was again increased by the operation described.

FOOTNOTES:

[23] Recherches sur les usages de la membrane du tympan et de l’oreille externe; par M. Felix Savart. _Annales de Chimie_, tom. xxvi. p. 1.

[24] The tuning-fork consists of a four-sided metallic rod, bent so as to form two equal and parallel branches, having a stem connected with the lower curved part of the rod, and contained within the plane of the two branches. The branches are caused to vibrate by striking one end against a hard body, whilst the stem is held in the hand. The sound produced by this instrument when insulated is very weak, and can only be distinctly heard when its branches are brought close to the ear; but instantly its stem is connected with any surface capable of vibrating, a great augmentation of sound ensues from the communicated vibrations. The facility of its insulation and communication renders it a very convenient instrument for a variety of acoustical experiments.

_On the Petromyzon Marinus_.

On entering the harbour of Dublin a few weeks ago, we were becalmed off the Hill of Howth, and to pass the tedious time until a breeze sprung up, we found some lines on board, and began to fish from the quarter-deck. We caught a number of grey gurnet; but our attention was particularly attracted by a pull of uncommon force on one of the lines. Having rendered assistance to the person who held it, we were all astonished to see rise out of the water a large fish, with apparently a double body, which, after floundering on the surface of the water, we pulled on deck. On examining this phenomenon for a short time, we were again surprized to see it separate into two parts; and then found that there were _two_ large fish taken up on the same hook, the head of one having been buried under the throat of the other, to which it had firmly attached itself. When separated by force, it wiggled about on the deck with extraordinary strength and agility, and again darted on its prey, to which [p073] it adhered so firmly, that it required very considerable exertion to detach it; for it suffered itself to be raised up by the tail, and shaken, still holding the other fish suspended from its jaws. When finally separated, it showed great ferocity, darting at every thing near it, and at last seizing the deck, which it held very fast, writhing with its tail and body as if in the act of tearing it to pieces. When detached, its teeth left a deep circular impression on the wood, the fibres of which were drawn into the cavity of its jaws, so as to be raised up in the form of a cone. I now directed, that it should be put into a bucket of sea water, in the hope of preserving it alive until we arrived in Dublin, but it died in a shorter time than could be expected, from the energy and activity it had displayed, long after the other fish was dead. We had handled it very roughly, and so perhaps had mortally hurt an animal otherwise very tenacious of life.

On examining the fishes, I found that which had taken the hook, was the _gadus Polachius_, or whiting Pollack. It was about two feet long, and it is probable its active enemy had fastened [p074] on it after it had been hooked; if _before_, it would indicate an extraordinary insensibility to pain in an animal that could attend to the calls of appetite, whilst another was preying on its vitals. The fish which had fastened on the pollack, was the _petromyzon marinus_, or sea lamprey. It was nearly three feet long, and resembled a large eel in shape. Its general colour was a dull brownish olive variegated with bluish blotches; the back darker, and the belly paler, inclining to yellow. The eyes were small, and the mouth large and oval; but when distended, circular. The inside of the jaws was deeply concave, and studded with circular rows of sharp triangular teeth, that issued from corresponding orange-coloured papular protuberances, which formed the gums; the tongue was short and crescent-shaped, furnished with a row of very small teeth round the edge. On the top of the head was a small orifice, or spout-hole, from whence it discharged the superfluous water taken at the mouth. But the circumstance that more particularly distinguished it, was that which gave rise to the vulgar error that it had sixteen eyes. On either side of the neck, commencing just below the real eyes, was a row of seven equidistant spiracles exactly resembling eyes; they are, however, holes lined with a red membrane, and all opening into the mouth, an apparatus to supply the place of gills, whose functions are to extract oxygen from the water, and so perform the office of lungs in aquatic animals. It had two dorsal fins, one on the lower part of the back, narrow, with a roundish outline; the other commencing where the first terminated. The spine was cartilaginous, without processes. The pericardium, containing a small heart, was a remarkably strong membrane, and the liver was as green as grass.

This fish is not uncommon in the North Seas, though it most abounds in the Mediterranean, where, from earliest times, it was esteemed a luxurious dish. Fish-ponds were purposely constructed to preserve it. On our coast, Pennant observes, that it is found most frequently at the mouth of the Severn, which river it sometimes ascends, where it is occasionally taken, firmly attached to a stone by its mouth, while its tail and body are waving freely to the current. Its adhesion at such times is so strong, that it may be lifted with a stone of twelve pounds weight appended to its mouth. This faculty is owing to its [p075] power of suction; while the circumstance of its circular jaws coming in close contact with the surface of the body excludes the external air within the cavity of the mouth, and so adheres like the hand placed on the cup of an air-pump. It is from this remarkable property, that its scientific name has been imposed[25]. Its vulgar name, lamprey, from lampetra, has a similar derivation. By the Romans it was named muræna. As this fish was well known and highly prized by the ancients, there is none that has been so frequently described and alluded to. Aristotle, Pliny, Tacitus, Columella, Ælian, Seneca, and Oppian, have mentioned its properties and habits, which correspond exactly with those I have described above. Pliny says, in the northern parts of France, and consequently contiguous to the British Isles, the lampreys have seven spots in the jaws, resembling the constellation of the plough, evidently the same as the eyes, which vulgar opinion assigns to the fish[26]. Their extreme voracity was such, that criminals were thrown among them to be devoured. Seneca relates, that Vedius Pollio, a Roman knight, ordered his servant, who had broken a crystal vase, to be thrown into a large pond of lampreys[27]; and Columella writes, that they were sometimes seized with a rabid fury, that resembled canine madness; in the access of which, they seized upon other fish, so that it was impossible to keep them in the same pond[28]; and to account for this extraordinary ferocity, Oppian and others assert, that the lamprey is impregnated by a serpent; the one issuing from the sea, and the other rushing down to the rocks, inflamed with madness, to consummate the impregnation; and adds, that the extraordinary intercourse was effected by the lamprey seizing the serpent’s head in its [p076] mouth[29]. This singular copulation was the reason why the Romans, who were immoderately fond of lampreys, did not wish to eat them, when impregnated by the supposed serpent. Horace, therefore, makes Nasidienus, among the blunders of his supper, serve it in that state[30].

Lampreys were a favourite dish with our own early monarchs. Henry II. died by eating them to excess. The celebrated Pope also owed his death to a surfeit of them. Doctor Johnson remarks in his life of the poet, that he was in the habit of cooking them himself in a silver saucepan. The Corporation of Oxford still make up a periodical pye of this fish for the king, in compliance with ancient usage. But lampreys have lost their rank at corporation feasts, in consequence of the more delicious and wholesome turtle being introduced into modern cookery.

I have never noticed lampreys in the Dublin fish-market; and though they are frequently used in the South of Ireland, I do not know if they have ever been made an article of food in Dublin, or the north, where they are rarely met with.

C.

FOOTNOTES:

[25] Petromyzon, _a_ πετρον, saxum, and μυζαω, sugere.

[26] In Gallia septentrionale murænis omnibus dextra in maxilla septenæ maculæ ad formam septentrionis aureo colore fulgent. PLIN. _Hist. Nat._ lib. ix. cap. 39.

[27] Fregerat unus ex servis crystallinum ejus; rapi eum Vedius jussit, nec vulgari quadam morte periturum, murænis objici jubebatur quas ingens piscina continebat.—SENECA _de Irâ_, lib. ii. cap. 40.

[28] Commisceri eas cum alterius notæ piscibus non placet, quasi rabie vexantur quod huic generi velut canino solet accidere. Sævitia persequuntur squamosos plurimosque mandendo consumunt. COLUMELLA _de Re Rusticâ_, lib. ix. cap. 17.

[29] Αμφι δε μυραινης φατις ερχεται ουκ αιδηλον
Ὥς μεν γαμει τε και εξ ἅλος ερχεται αυτη
Προφρων ἱμειουσα παρ’ ιμειροντι γαμοιο
Ητοι ὁ μέν φλογεῃ τεθοωμενος ενδοθι λυσσῃ
Μαινεται ἔις φιλοτητα και ἔγγυθι συρεται ἅκτης
Πικρος ὄφις. κ.τ.λ.—OPPIAN, _Halieut._ lib. i. V. 554.

[30] Adfertur squillas inter muræna natantes, In patinâ porrecta: “hæc gravida,” inquit, “Capta est.”—HOR. lib. ii. Sat. 8. lin. 46.

_Observations upon the Motion of the Leaves of the Mimosa Pudica_. [To the Editor of the Quarterly Journal of Science.]

Dear Sir,

Towards the latter part of this summer, Mr. Gilbert Burnett and myself made several experiments with a view to ascertain the nature of the movements exhibited by the sensitive plant. We afterwards found that the greater part of the facts which we had observed, had been previously described by Mr. Lindsay [p077] and Dr. Dutrochet. Mr. Lindsay’s observations are to be met with in a MS. preserved in the library of the Royal Society, which is dated July 1790: this essay is alluded to by Dr. Smith in his “Introduction to Botany.” Dr. Dutrochet’s experiments were published in his “Recherches anatomiques et physiologiques sur la Structure intime des Animaux et des Végétaux,” which appeared in 1824. With the latter author the reputation of originality is likely to rest: not undeservedly, indeed, as there is no reason to suppose that _his_ experiments were suggested by a knowledge of those performed by Lindsay. It is, however, an act of literary justice to secure to Mr. Lindsay the credit of undoubted priority in describing the phenomena which he noticed in common with Dutrochet. I have drawn up the following remarks partly for this purpose—partly to have an opportunity of mentioning some circumstances which escaped the observation of both experimentalists.

The leaves of the Mimosa Pudica consist either of one or two or three pairs of leaflets, and occasionally terminate by an odd one. Each leaflet bears from twenty to sixty subleaflets, which are disposed in pairs. The petiole or stalk of each leaf, at the extremity which is attached to the branch or stem of the peant, swells into an intumescence varying from three to five in length. A similar intumescence, of proportionate dimensions, is seen upon each subpetiole, where it is articulated with the petiole, and upon the base of the stalk of each subleaflet: the intumescence is the part in which motion takes place.

During the day-time the petioles are observed to have a direction upwards, or rather to form an acute angle with the upper part of the stem or branch, to which they are attached: the subpetioles are divergent: the subleaflets are spread out, so as to lie nearly in one plane. (_Fig._ 1.)

During the night the petioles are found to be depressed; the subpetioles to be drawn together, the subleaflets folded, the upper or solar surfaces of each pair being brought into contact. (_Fig._ 2.)

The leaves rise, the leaflets diverge, and open by throwing down their subleaflets, at daybreak: the opposite changes occur about sunset. The experiments that are to be described, are supposed to be performed in the day-time. [p078]

If a terminal subleaflet be pinched with forceps, or cut with scissors, it rises, together with its fellow; then the next pair rise; then the next; and so on in succession, till all the pairs of subleaflets upon the same subpetiole are folded. In a little time afterwards, the petiole is bent downwards at its intumescence; and in a few seconds more the remaining leaflets upon the same petiole fold their subleaflets in pairs, from the base towards the point of the leaflet.

If a subleaflet be burnt, instead of being cut or pinched, the phenomena above described occur more rapidly: and after they have taken place, the adjoining leaves upon the same branch are bent down in succession, their leaflets brought together, and their subleaflets folded. If the plant be very vigorous and lively, an impression [p079] made upon one leaf affects the rest in succession. It is well known that the stem, branches, flowers, and roots of the sensitive plant have no motion. But M. Desfontaines observed that, on touching the roots with sulphuric acid, the leaves become folded; and M. Dutrochet obtained a similar result on burning either the flower or the stem.

If the plant be shaken, all the leaves are simultaneously thrown down, and their leaflets folded. Mr. Lindsay attempted to elucidate the action of the intumescence in raising and depressing the petiole, in the following manner. He cut out a portion from the upper or solar surface of the intumescence; after which he found that the petiole, upon recovering, rose higher than before, (_Fig._ 3.) From another leaf he removed the inferior portion of the intumescence: he found, upon _this_ injury, that the leaf declined more than before, and did not again rise, (_Fig._ 4.) He noticed that a thin slice, pared from either surface of the intumescence, has a like effect, but in a less degree than a deep excision: and he found that when similar experiments are made upon the intumescence of the subpetiole, there is no essential difference in the result.

Thus Mr. Lindsay discovered, that the force which raises the petiole exists in the lower part of the intumescence, and that which depresses it, in the upper. He seems to have considered that the temporary excess of force in either part is produced by an impulsion of the sap from the vessels of the yielding portion into those of the opposite portion. [p080]

Dr. Dutrochet viewed these phenomena in some respects more justly. He remarked, in addition to what Lindsay had observed, that if, instead of the upper and under surface, the lateral part of the intumescence be removed, the petiole becomes not raised or deflected, but inclined towards the side on which it is injured (_Fig._ 5); and that if longitudinal slices of the upper, or under, or lateral portions of the intumescence are immersed in water, these separate slices immediately become incurvated, that edge being concave which looks towards the axis of the intumescence. From these facts Dutrochet inferred that the texture of the intumescence possesses some modification of irritability; that, when excited, each length of the intumescence (to use a very imperfect expression) forcibly assumes an incurvated figure, like a curved spring returning from a state of temporary extension; that the petiole is raised, when the action of the lower part of the intumescence predominates; is depressed, when the upper portion acts with increased energy.

Mr. Burnett and myself had arrived at very similar conclusions respecting the agency of the intumescence, before we became acquainted with the inquiries of Lindsay and Dutrochet.

In Dutrochet’s able researches, a more exact analysis, however, was obtained of the functions of this part. He discovered that the cortex of the intumescence is the seat of its irritability: for upon wholly removing the bark, so as to expose the ligneous substance, the petiole was found to have been rendered motionless. Nevertheless, the intumescence, thus mutilated, remains capable of transmitting an impression made upon its leaflets to the leaves adjoining, Dutrochet further ascertained, that the ligneous substance alone is fitted to convey the peculiar stimulus, which spreads, from a point of the plant that has been irritated, to the adjoining leaves.

The experiments already mentioned appear to explain the mode in which the elevation and depression of the petiole, and the divergence and approximation of the subpetioles are produced. It is probable that the contrivance for folding and expanding the subleaflets is of a similar nature. Mr. Burnett and myself conjectured that each subleaflet is raised by the under part of the intumescence that exists at its base, and [p081] depressed by some action of the upper portion of the same intumescence. In trying the soundness of this hypothesis, we met with the following evidence in its favour:—

Mr. Lindsay had observed, that at the moment when the petiole is depressed, the under part of its intumescence assumes a deeper colour. But the under part of the intumescence of the petiole is the portion which is shortened during its depression, and which is overcome on this occasion by the superior force of the upper portion.

Now it is to be remarked that in the subleaflets the upper part of the little intumescence belonging to each corresponds, in one respect alluded to, with the lower portion of the intumescence of the petiole; _it is the portion shortened when the leaf is folded_. And we found, upon examination, that it likewise distinctly changes colour at the moment when the subleaflet rises, while the under surface of the intumescence of the subleaflet does not change its hue.

In pursuing this inquiry, another point of correspondence between the mechanism which depresses the petiole, and that which raises the subleaflets, was stated, which has yet additional interest.

When the plant is not in its most lively state, the under surface of the intumescence of the subleaflet (_b_, _Fig._ 2,) and the upper surface of the intumescence of the petiole (_a_, _Fig._ 6,) may be pricked with a needle, without producing action. But if the opposite surfaces, those namely, which change colour and are shortened when the petiole is depressed and the subleaflets folded, are touched with the point of the needle these actions are instantaneously produced. Here the [p082] subleaflet is most delicately sensible; _a slight touch_ with the point of a needle upon the upper surface of the intumescence of the subleaflet (_c_, _Fig._ 1,) causes the single subleaflet so stimulated to rise; and in this manner all the subleaflets upon one side of a leaflet may be raised, their fellows remaining expanded: if the touch be something sharper, the fellow subleaflet rises at the same time; if ruder still, the next pair of leaflets fold directly afterwards, and the irritation then proceeds entirely through the leaflet. But the most satisfactory and curious results are obtained on stimulating the extension surface of the intumescence of the petiole. The needle may be applied to every point upon the upper or solar half of the intumescence of the petiole (_a_, _Fig._ 6,) without producing any visible effect; but if the irritation be applied upon the under half, (_d_, _Fig._ 6,) either quite below or laterally, the petiole is immediately depressed. The transition is abrupt from the surface against which the needle may be made to prick, without exciting action, to one which, when the needle reaches it, causes the petiole to be instantaneously thrown down.

It appears, therefore, that each intumescence has a surface especially adapted to receive mechanical impressions; which surface is placed on the side of the intumescence opposite to that, by which the consequent motion is produced. A curious but vague analogy may be traced between these surfaces of the sensitive plant and the organs of sense in animals.

We painted with a thick layer of lamp-black in oil the intumescence of different petioles in different ways; the upper surface of one, the under surface of another, the side of a third. The experiment was followed by no sensible effect. After a few minutes the petioles, which had been thrown down by the operation, rose again in each case, and fell again as readily as before upon being stimulated afresh.

We tried what result would ensue upon slitting the intumescence of the petiole horizontally. The petiole, after this injury, did not recover its usual direction; the intumescence appeared to have wholly lost its properties; the leaf seemed to depress the petiole by its weight alone, yet the leaflets expanded, and exhibited their usual irritability, upon the depending stalk. The same effect, however, was observed, when the [p083] intumescence was divided by a longitudinal incision, made vertically instead of horizontally.

I have already mentioned that Dutrochet discovered that the ligneous fibre is the channel, along which an impression is conveyed from one part to another. Mr. Burnett and myself had made one or two experiments upon the course which the irritation follows when spreading from leaflet to leaflet, where several are placed upon the same petiole.

If the upper third of a petiole bearing four leaflets be divided longitudinally, the irritability of the leaflets remains for many days unimpaired; upon cutting with scissors one subleaflet after the plant has recovered itself, the irritation is observed to descend the wounded leaflet, and then to pass to that adjoining upon the same side of the petiole: afterwards the petiole falls, but there the effect stops; it does not extend to the two other leaflets; the direct route is cut through, and the irritation seems to find no circuitous way, as might have been expected, perhaps through the intumescence of the petiole back again to the leaflets, on its summit. If on a petiole, bearing four leaflets, a lateral incision be made, cutting the petiole half through it at a point between the two leaflets which are situated on one side, upon irritating either of the leaflets, between which the incision has been made, it folds its subleaflets; then the two opposite leaflets fold _their_ subleaflets; and _last of all_, the leaflet next adjoining that first irritated, but isolated from it by the incision, becomes folded.

In the few remarks which I have thus put together, I have quoted Lindsay and Dutrochet only as far as their researches anticipated my own: I leave unnoticed many experiments, in several of which these authors are again found to have accidentally coincided. The experiments to which I allude do not, however, serve to illustrate the nature of the motion exhibited by the sensitive plant, to the examination of which subject alone my attention was, in the present instance, directed, in the expectation that it might throw light upon the obscure and interesting subject of muscular action.

I remain, my dear Sir, Your’s truly, HERBERT MAYO.

19, _George Street, Hanover Square_, _August 29, 1827_.

[p084]

_Experiments on the Nature of Labarraque’s disinfecting Soda Liquid_. By M. Faraday, F.R.S., Corr. Mem. R. Acad. Sciences, Paris, &c. &c.

1. The following experimental investigations relate to the nature of that medicinal preparation which M. Labarraque has lately introduced to the world, and named _Chloride of oxide of Sodium_. They were occasioned by the accounts which were given of this and other substances of similar power, to the members of the Royal Institution, at two of their Friday evening meetings[31]; the value of the preparation, the uncertainty of its nature, and the inaccuracy of its name, all urging the inquiry.

2. In the first instance the inquiry was directed to the nature of the action exerted by chlorine gas upon a solution of carbonate of soda, questions having arisen in the minds of many, whether it was or was not identical with the action exerted by the same gas on a solution of the caustic alkali, and whether carbonic acid was evolved during the operation or not. Chlorine gas was therefore carefully prepared, and after being washed was sent into a solution of carbonate of soda, in the proportions directed by M. Labarraque; _i. e._ 2800 grains of crystallized carbonate of soda were dissolved in 1.28 pints of water; and being put into a Woulfe’s apparatus, two-thirds of the chlorine evolved from a mixture of 967 grains of salt with 750 grains of oxide of manganese, when acted upon by 967 grains of oil of vitriol, previously diluted with 750 grains of water, were passed into it; the remaining third being partly dissolved in the washing water, and partly retained in the open space of the retort and washing vessel. The operation was conducted slowly, that as little muriatic acid as possible might be carried over into the alkali. The common air ejected from the bottle containing the solution was collected and examined; but from the beginning to the end of the operation not a particle of carbonic acid was disengaged from the solution, although the chlorine was readily absorbed. Ultimately a liquid of a very pale [p085] yellow colour was obtained, being the same as M. Labarraque’s soda liquor, and with which the investigations were made that will hereafter be described.

3. An experiment was then instituted, in which the effect of excess of chlorine, upon a solution of carbonate of soda of the same strength as the former, was rendered evident. The solution was put into two Woulfe’s bottles, the chlorine well washed and passed through, until ultimately it bubbled through both portions without absorption of any appreciable quantity. As soon as the common air was expelled, the absorption of the chlorine was so complete in the first bottle, that no air or gas of any kind passed into the second, a proof that carbonic acid was not liberated in that stage of the experiment. Continuing the introduction of the chlorine, the solution in the first bottle gradually became yellow, the gas not being yet visible by its colour in the atmosphere above the solution, although chlorine could be detected there by litmus paper. Up to this time no carbonic acid gas had been evolved; but the first alkaline solution soon acquired a brighter colour, and now carbonic acid gas began to separate from all parts of it, and passing over into the second bottle, carried a little chlorine with it. The soda solution in the first bottle still continued to absorb chlorine, whilst the evolution of carbonic acid increased, and the colour became heightened. After some time the evolution of carbonic acid diminished, smaller quantities of the chlorine were absorbed by the solution, and the rest passing into the atmosphere in the bottle, went from thence into the second vessel, and there caused the same series of changes and actions that had occurred in the first. The solution in the first bottle was now of a bright chlorine yellow colour, and the gas bubbled up through it as it would through saturated water.

4. When the chlorine had saturated the soda solution in the second bottle, and an excess of gas sufficient to fill several large jars had been passed through the whole apparatus, the latter was dismounted, the solutions put into bottles and distinguished as the saturated solutions of carbonated soda; they were of a bright greenish-yellow colour, and had an insupportable odour of chlorine.

5. The saturated solution (4) was then examined as to the [p086] change which had been occasioned by the action of the chlorine. It bleached powerfully, and apparently contained no carbonated alkali: but when a glass rod was dipped into it and dried in a warm current of air, the saline matter left, when applied to moistened turmeric paper, reddened it considerably at first, and then bleached it; and this piece of paper being dried and afterwards moistened upon the bleached part, gave indications of alkali to fresh turmeric paper.

6. A portion of the saturated solution (4) being warmed, instantly evolved chlorine gas, then assumed a dingy appearance, and ultimately became nearly colourless; after which it had an astringent and saline taste. Being evaporated to dryness at a very moderate temperature, it left a saline mass, consisting of much common salt, a considerable quantity of chlorate of soda, and a trace of carbonate of soda. This mixture had no bleaching powers. The dingy appearance, assumed in the first instance, was found to be occasioned by a little manganese which had passed over into the solutions, notwithstanding the care taken in evolving and washing the gas.

7. From these experiments it was evident that when chlorine was passed _in excess_ into a solution of carbonate of soda (3), the carbonic acid was expelled, and the soda acted upon as if it were caustic, a mixture of chloride of sodium and chlorate of soda being produced; with the exception of the small portion of carbonate of soda which, it appears, may remain for some time in the solution in contact with the excess of chlorine at common temperatures, without undergoing this change. The quantities of chloride of sodium and chlorate of soda were not ascertained, no doubt being entertained that they were in the well-known proportions which occur when caustic soda is used.

8. The Labarraque’s soda liquor which had been prepared as described (2), was now examined relative to the part the chlorine played in it, or the change the alkali had undergone, and was soon found to be very different to that which has been described, as indeed the experiments I had seen made by Mr. Phillips[32] led me to expect. The solution had but little odour of chlorine, its taste was at first sharp, saline, scarcely at [p087] all alkaline, but with a persisting astringent biting effect upon the tongue. When applied to turmeric paper, it first reddened and then bleached it.

9. A portion of the solution (2) being boiled, gave out no chlorine; it seemed but little changed by the operation, having the same peculiar taste, and nearly the same bleaching power as before. This is a sufficient proof that the chlorine, though in a state ready to bleach or disinfect, must not be considered as in the ordinary state of solution, either in water or a saline fluid; for ebullition will freely carry off the chlorine under the latter circumstances.

10. A portion evaporated on the sandbath rather hastily, gave a dry saline mass, quite unlike that left by the _saturated solution_ already described (6); and which, when dissolved, had the same astringent taste as before, and bleached solution of indigo very powerfully: when compared with an equal portion of the unevaporated solution, which had been placed in the mean time in the dark, its bleaching power upon diluted sulphate of indigo was 30, that of the former being 76. Another portion, evaporated in a still more careful manner, gave a mass of damp crystals, which, when dissolved, had the taste, smell, and bleaching power of the original solution, with almost equal strength.

11. These experiments shewed sufficiently that the whole of the chlorine had not acted upon the carbonate of soda to produce chloride of sodium, and chlorate of soda; that much was in a peculiar state of solution or union which enabled it to withstand ebullition, and yet to act freely as a bleaching or disinfecting agent; and that probably little or none had combined with the sodium, or been converted into chloric acid. To put these ideas to the test, two equal portions of the Labarraque solution were taken; one was put into a large tube, closed at one extremity, diluted sulphuric acid was added till in excess, and then air blown through the mixture by a long small open tube, proceeding from the mouth, for the purpose of carrying off the chlorine; the contents of the tube were then heated nearly to the boiling point, air being continually passed through. In this way all the chlorine which had combined with the carbonated alkali without decomposing it, was set free by the sulphuric acid, and carried off by the current of air and vapour, whilst any which had acted chemically upon the alkali would, [p088] after the action of the sulphuric acid, be contained in solution as muriatic and chloric acids, and from the diluted state of the whole, would not be removed by the after-process, but remain to be rendered evident by tests. The other portion being diluted, had sulphuric acid added also in excess, but no attempt was made to remove the chlorine. Equal quantities of these two portions in the same state of dilution were then examined by nitrate of silver for the quantities of chlorine sensible in them, and it was found that the latter portion, or that which retained the whole of the chlorine thrown into it, contained above sixty times as much as the former.

12. Now although it may be supposed that in the former portion that part of the chlorine, which, in acting energetically, had produced chloric acid, could not be detected by the nitrate of silver, yet more than a sixth of the small portion which remains cannot be thus hidden; and even that quantity is diminished by the sulphuric acid present in excess, which tends to make the chlorine in the chlorate sensible to nitrate of silver: so that the experiment shews that nearly 59 parts out of 60 of the chlorine in M. Labarraque’s liquid are in a state of weak combination with the carbonated alkali, and may be separated by acids in its original condition; that this quantity is probably wholly available in the liquid when used as a bleaching or disinfecting agent; that little, if any, of the chlorine forms chloride of sodium and chlorate of soda with the alkali of the solution; and that the portion of chlorine used in preparing the substance which is brought into an inactive state, is almost insensible in quantity.

13. The peculiar nature of this compound or solution, with the results Mr. Phillips had shewn me (8), obtained by evaporation of a similar preparation to dryness, induced me to try the effects of slow evaporation, crystallization, heat, and air upon it. In the first place five equal portions of the solution prepared by myself were measured out: two were put into stoppered bottles, two were put into basins and covered over with bibulous paper, and one was put into a basin which was left open; all were set aside in an obscure place, and remained from July 16th to August 28th. Being then examined, the portions in the basins were found crystallized and dry; the crystals were large and flat, striated and imperfect, resembling those formed [p089] in a similar way from carbonate of soda. They were not small and acicular, were nearly alike in the three basins, and had effloresced only on a few minute points. A part of one portion, when dissolved, gave a solution, having an alkaline taste, without any of the pungency of Labarraque’s liquid; and which, when tested by turmeric paper, reddened, but did not bleach it.

14. One of these portions that had effloresced least was selected, and being dissolved, was compared in bleaching power upon diluted sulphate of indigo, with one of the portions of solution that had been preserved in bottles. The former had scarcely any visible effect, though sulphuric acid was added to assist the action; a single measure of the indigo liquor coloured the solution permanently blue, whereas seventy-seven such measures were bleached by the portion from the bottle. Hence the process of slow crystallization had either almost entirely expelled the chlorine, or else had caused it to react upon the alkali, and by entering into strong chemical combination as chloride and chlorate, had rendered it inert as a bleaching or disinfecting agent.

15. From the appearance of the crystals there was no reason to expect the latter effect; but to put the question to the proof, one of the evaporated portions, and one of the fluid portions contained in the bottles, were acted upon by sulphuric acid, heat, and a current of air, in the manner already described (11), to separate the chlorine that had not combined as chloride or chlorate. They were then compared with an equal portion of the solution, which retained all its chlorine, nitrate of silver being used as before: the quantity of chloride indicated for the latter portion was 60 parts; whilst that of the fluid portion deprived of as much free chlorine as could be, by sulphuric acid and blowing, was 6 parts; and for the evaporated and crystallized portion, similarly cleared of free chlorine, only 1.5 parts.

16. This result, as compared with the former experiment of a similar kind (11), shewed, that though reaction of the chlorine on the carbonate had taken place in the evaporated portion, it was only to a very slight extent, since the chlorine was almost as much separated from it by the process altogether, as it had been from the recent preparation by sulphuric acid, blowing, and heat. The experiment shewed also that there [p090] was a gradual reaction of the chlorine and alkali in the fluid preparation, proceeding to a greater extent than in the evaporated portion; for chlorine, equal to five parts, was found by the nitrate of silver to remain. Hence this preparation is one which deteriorates even in the small space of forty-three days. Whether the effect will proceed to any great extent, prolonged experiments only can shew.

17. From an experiment made upon larger quantities of the Labarraque liquor, it would appear that the force of crystallization alone is sufficient to exclude the chlorine. A quantity was put into an evaporating basin, and left covered over with paper from July 16th to August 28th. Being then examined, a few large crystals were found covered over with a dense solution; the whole had the innocuous odour of Labarraque’s fluid, and the fluid the usual acrid, biting taste. The crystals being separated, one of the largest and most perfect was chosen, and being well wiped on the exterior, and pressed between folds of bibulous paper, was rubbed down in water, so as to make a saturated solution. This had no astringent taste like that of Labarraque’s fluid, or the mother-liquor, but one purely alkaline; and when applied to turmeric paper, reddened, but did not bleach it. Equal portions of this saturated solution and of the mother-liquor were then compared in bleaching power, acid being added to the former to assist the effect: it was found, notwithstanding that portions of mother-liquor must have adhered to the crystal, that its solution had not 1/21th part the power of the mother-liquor. This, in conjunction with the other experiments, is a striking instance of the manner in which the carbonate of soda acts, as a simple substance, with the chlorine in the solution. The crystal itself had never been in contact with the air: but whether it should be considered as the excess of carbonate of soda only which crystallized; or whether it is essential to the formation of these crystals that chlorine should simultaneously be given off into the air; or what would take place, if the water were abstracted without the evolution of chlorine, I have not determined.