« ZurückWeiter »
and proceed to detail the results of some more recent researcheswhich several of the most eminent chemists of the time already speak of as having at length settled the whole question—in other words, led to the discovery of a means of preventing this disease in timber, at once universally applicable, cheap of cost, and unattended with any countervailing disadvantages to the health of man. We shall not be so rash as to pronounce any fixed judgment, while his majesty's Board of Admiralty see reason to continue their trials of the proposed panacea; for we can have no doubt that they will speak out as soon as an honest sense of duty to the public will permit them to do so. But we think the progress already made in their cautious line of experiment so considerable, that we shall be doing a service by directing general attention to the business, and stimulating private ship-builders, architects, and proprietors of woodland, to institute experiments of their own in various parts of the country, the results of which, if properly observed and recorded, may be of extreme value not only to themselves but to the community.
At the beginning of this century one writer maintained that fungous plants were the causes of dry rot; another answered him by exhibiting gigantic ravages of dry rot, where there were no fungi whatever; and, not to weary our readers with needless repetitions, botanists and chemists were at length content to acquiesce in old Pliny's doctrine, that this species of disease in timber originates simply in the putrefaction of the vegetable juices of the wood, and may develope itself in the growth of fungi or otherwise, without being either less or more fatal in its effects. Then came great controversies as to these vegetable juices thenselves :—some holding, that if the shipwright chipped off all the outer wood or alburnum, in which the juices are far more copious than in the heartwood, the danger would be at least reduced to a trifle ;-—while others (of whom Buonaparte approved) were for limiting the felling of timber to the three months of winter proper; —and those who doubted the efficacy of either of these plansbelieving that dry rot begins with the heartwood under one set of circumstances, as infallibly as with the alburnum under another, and that the vegetable juices are by no means entirely out of the trunk or branches either, even in the prime of January-argued in favour each of his own scheme for dealing with the juices in the felled timber ;-one recommending us to attack them by desiccation; a second by dissolution in running water; a third by antiseptics, such as steeping in brine ; a fourth by the exhibition of oleaginous substances to prevent the access of the atmospheric air, &c.-as to all which views and prescriptions see copious details in the article of the Encyclopædia above referred to.
* Among the documents printed by Mr. Kyan is a very distinct report in his favour, drawn up, after a trial of three years, by Sir Robert Sepping: and probably the Board's attention to the subject has been in some degree interrupted, in consequence of Sir Robert's retirement from the public service, which occurred shortly after his signature was affixed to that certificate.
There can be no doubt as to the partial efficacy of all these plans; but experience has shown, that no one of them can be, in all circumstances, relied on practically as a panacea for dry rot. The process of desiccation by exposure to air and wind is the only one of them that has been largely adopted in our public establishments; but in innumerable instances its failure has been lamentably and even early apparent. The statements of Mr. Knowles on this head are precise and irrefragable. In every dockyard, (he says,) in spite of the best care and arrangement, it has often been the lot of the shipwright to find, that while the external parts of the log, exposed to a free current of air, remained without spot or blemish, the work of corruption had begun in the interior, to which the air could not penetrate with sufficient power. Whole stacks of timber would be found healthy for a certain number of inches inwards, but bored through at the centre with a creeping and spreading sore, from the fermentation of the juices compressed in the heart of oak.'* Exactly the same has been the result of multifarious, though less extensive, experiments with oleaginous substances. None of them penetrate deep enough to protect the heartwood, when it is exposed to the vicissitudes of heat and cold, moist and dry atmospheres. Nor has the scheme of dissolving the vegetable juices, so as to destroy their vitality, by steeping the timber in water, been able to bear the test on any large scale. In the case of such a customer as the navy, its mere tediousness and consequent expense, even were it proved to be perfectly effective, would be an insurmountable objection. As to the steeping in brine, we need only refer to some authorities quoted in this Journal on a former occasion, and which prove, beyond cavil, that the attraction for moisture which deliquescent salts possess, would render a vessel built of timber thus dealt with a complete hygrometer,that the interior would be in a dripping state, which would not only expose the ship to destruction by wet rot, but be incalculably dangerous to the health of the ship's company,--and lastly, that the iron work would be rapidly corroded.
* We quote one of the instances attested by Mr. Knowles:In the middle of the year 1814 a stack of timber was formed in Deptford yard, according to a plan recommended by Mr. Sowerby, and this was carried on under his inspection. The method of forming the pile was as follows:- There were sixteen piers formed of brick, with stone caps placed in four rows, upon pavement, lying at an angle of inclination to carry off the rain-water : these were three feet six inches in height, and ten feet asunder. On each pier two pigs of iron ballast were laid, which being six inches square and two feet ten inches long, made the height of the supports four feet. On these, pieces of sided oak timber were laid as skids, and other pieces crossed them, with a considerable separation between each, and by this manner of stowage the pile was raised several tiers. The timber remained in this state till June 1820, a period of five years, when it was unstacked for use ; although it was a little rent, it had externally a fine and sound appearance, but the whole was found to be more or less internally decayed, except in those parts where the timber had crossed; the heart of the several pieces resembled the soft spongy sap-wood, or, as it is sometimes called, touchwood, but there was no appearance of fungus either externally or internally.'
Regarding, as far as we can perceive, the growth of fungi as the primary evil to be guarded against, the late illustrious philosopher, Sir Humphry Davy, threw out, in one of his early lectures at the Royal Institution, a hint that a solution of the deutochloride of mercury, which he had tried with success as a means of preserving insects, might perhaps be found available on a larger scale, and especially in the case of vegetable substances; but no experiments appear to have followed this suggestion, chiefly, we believe, because Davy himself expressed, shortly afterwards, a suspicion that, if such experiments were ever so successful, a poisonous atmosphere might be generated within a ship, or even a dwelling-house, constructed of timbers which had been saturated with such a preparation.* The hint, in short, had the fate of so many now famous articles in the Marquis of Worcester's • Century of Inventions :'—it found a place in every successive treatise on dry rot; but no one thought of putting it to the test; until a distiller of the city of London, who had never, it is said, heard of Davy's obiter dictum, in the course of some experiments on vegetable infusions, became so much impressed with the virtues of the very application which Davy had pointed out, that he was induced to begin a series of experiments as to wood also ;and hence the novel aspect under which the whole subject of dry rot at this moment presents itself.
The theory of this ingenious person, in as far as we can gather it from his specification, and some printed documents now before us, and we must add from a very clever lecture lately delivered by Mr. Faraday, may be considered as founded on the great truth thus succinctly stated by Fourcroy : The aim of nature in exciting fermentation is to render more simple the compounds formed by vegetation and animalization, and to employ these in new combinations. Mr. Knowles, in commenting on Fourcroy's dictum, says,
• Thus is the great law of nature fulfilled, that the death of one body shall give life to others. When the animal dies, and fermentation takes place, flies deposit their eggs, maggots are formed, and the fleshy parts are destroyed; when the vegetable body falls, it is eaten
* This suspicion, we believe, occurred to Sir Humphry Davy, and also to Mr. Faraday, when they were consulted by Earl Spencer on the appearance of dry rot in his Lordship’s magnificent library at Althorp. VOL. XLIX, NO, XCVII,
by worms of another kind, or destroyed by fungi; and if, in consequence of the employment of art, the duration of either is extended, that slow but sure destroyer, Time, at length renders them to their native earth, to serve, in their turn, for nutriment to others.'— Knowles, p. 112.
In the next paragraph Mr. Knowles advances another and a very important step :
• When an animal or vegetable body is deprived of life, the very principles which were the causes of its nutriment become the means of its decay. To bring about decomposition the same agents are necessary as to promote vegetation, -air, heat, and moisture, under proper modifications and combinations. In a vegetable body, when the fermentative process begins, the vessels or fibres of which it is composed are put in motion ; a separation of them takes place; the volume is consequently enlarged, and it generally suffers an alteration in colour. As the process advances towards putrefaction, heat is evolved,
and carbonic gas is disengaged.'— Ibid. Mr. Knowles, in this last passage, approached the verge of his successor's theory; which may be thus briefly stated. In the germination which converts the acorn into an oak, and in the putrefaction which reduces the felled tree to a bed of fungi, or a hive of insects,—the same great vegetative principle is at work. Vegetable albumen (combined, in various proportions, with farinaceous, mucilaginous, and saccharine matter) is the primary constituent of every seed. When exposed to atmospheric air under a certain temperature,—not lower than 32° nor higher than 100° of Fahrenheit,—the germinating power is brought into action, and the seed becomes a tree. The first year's growth forms the pith, the alburnum, and the bark : in the following year, or years, the pith becomes heart-wood, and when that is once formed, every succeeding season adds another concentric layer of alburnum, which in its turn becomes ultimately heart-wood. The bark has an expansive growing power, so as to admit the yearly extension of the alburnum ; but it has also a strong compressive energy, expelling moisture from the layers that successively assume the character of heart-wood, but not expelling the vegetable albumen, which, squeezed into a concrete form, remains shut up in the interstices, even to the very centre of the tree. The active vitality of the tree is in the alburnum, through the vessels of which, perpendicularly and also laterally, the sap ascends and circulates; but the principle of vitality,--the albumen of the parent seed,-continues to be present, though dormant, in the compactest tissue of the heart of oak; and capable, even after the lapse of centuries, during which it has been preserved from the action of air and moisture, of exhibiting its vegetative power on being exposed to these influences.
If we grant these premises,-in support of which we are referred to a very beautiful chapter in Mr. Lindley's recent work on botany,
and to innumerable undoubted facts, recorded in existing treatises on dry rot, especially in the masterly Essay in the Supplement to the Encyclopædia Britannica,- it will begin to be pretty clear that no process of desiccation ought to be the object of the physiologist who would strike at the root of this malady; but that he ought to search for the means of destroying the latent element of vitality in the central body of the tree, -of extirpating the dormant life of the concrete albumen. The practical inquirer, whose operations have suggested this paper, asserts, accordingly, that he has satisfied himself, by a course of experiments continued during not less than ten years, that this object has been attained,--that the primary cause of all vegetable fermentation is neutralized by the deutochloride of mercury, exactly as Sir H. Davy had ascertained its efficacy in neutralizing the primary element of animal decay. The true principle of action, he says, in almost every antidote, is affinity for the bane or poison to be neutralized or destroyed. Albumen, in animal and in vegetable substances, is the main element of physical vitality, and consequently of fermentation and putrefaction. Every tyro who walks an hospital knows that white of egg is the simplest antidote to corrosive sublimate; and in like manner, when a solution of sublimate is applied to timber, it at once penetrates the alburnum, and then fies to the heart-wood, — combining with the albumen, whether in an active or a dormant state, and killing it.
Mr. Faraday, of the authority of whose name we need not say anything, expressed himself in the outset of his lecture of the 22d of February last, as having been very soon impressed that this theory, and the practice thereon founded, would, in all probability, stand the test of experiment. The subject appeared so important in itself, and the doctrine of the new application so just ex facie, that he took considerable pains in examining into the matter-visiting from time to time the tanks of the patentee's establishment, watching the progress of the experiments at Woolwich, and also trying the thing for himself in a variety of ways, in his own laboratory. He proceeded to narrate, in the first place, the history of the experiments which had been made in London and at Woolwich, as to separate pieces of wood, and to exhibit to his audience abundant specimens of the results. The display was a most curious one,—but
'Segnius irritant animos demissa per aures
Quàm quæ sunt oculis subjecta fidelibus ;' and we shall content ourselves with a very brief and imperfect repetition of things, which certainly must have left an extraordinary impression on the mind of every eye-witness.
The fungus pit’ at Woolwich is a subterranean chamber lined with wood in the worst possible stages of corruption: it is kept extremely damp, generates carbonic acid gas in profusion,