« ZurückWeiter »
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 flies 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 er 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,
and, in short, forms, as its name implies, a perfect hot-bed for the growth of all those fungi that used to be considered as the causes, but which are only the most usual symptoms, of dry rot. It is a proverb among the people of the dockyard, that a month in the hole is worse for a bit of timber, than ten years in almost any possible situation out of it:—and the government, pestered with the eternal applications of the rot-doctors, have hitherto found their safety-valve in this fungus pit. Mr. Knowles concludes one of his chapters with a distinct statement that no prepared timber, exposed during twelve months to the action of this ordeal, had, unless insulated by some other substance, entirely resisted the influence of the gas.' (p. 55.) We have ourselves visited this noxious place, and seen an hour and a half elapse, after opening the trap-door, before a candle would burn six inches beneath the surface. Blocks of timber-oak, elm, pine, beech, &c.—prepared with the solution of sublimate, have now, as Mr. Faraday said, and as the printed documents before us prove distinctly, stood the test of the fungus pit, without exhibiting the slightest symptom of decay, during no less a period some of them than five years: and these, instead
of being insulated by means of some heterogeneous substance, had been lying on the fungus-spread floor of the dungeon, each with an unmedicated fragment of the very same tree, and of the like bulk, close by its side -every one of which unprepared pieces was found at the opening of the pit in rapid progress to decomposition. The results of various experiments, instituted by Sir Robert Smirke, the eminent architect, with a view to his own professional business, were in like manner detailed, and his evidence as to the power of timbers prepared in this method to resist the action of dropping eaves, &c. during a course of time sufficient to bring utter decay upon unprepared ones similarly exposed, was not less satisfactory than the upshot of the long trials at Woolwich.
The primâ facie efficacy of the application was illustrated, as some thought even more remarkably, by the exhibition of pieces of canvass, and even of delicate calico cloth, which had been placed during from two to three months on the floor of the fungus pit. The prepared pieces came out entirely sound, while, of the unmedicated counterparts, there remained 'nothing but a few mildewed strings that fell to pieces at the touch.
The lecturer stated, on the authority of Mr. Kyan, that cubes of oak, Memel pine, &c., containing each 216 cubical inches, imbibe, notwithstanding the difference of their structures, as nearly as can be measured, the very same quantity of the solution—about five ounces each; a quantity so small, that the expense of the operation is a mere trifle, compared with the result. "The process is of course rapid in a plank, compared with a solid log. Fir deals take in their quantum within forty-eight hours--a beam of oak is not saturated under a month; but what is a month, when we think of the years always considered necessary for the seasoning of timber in the usual process of drying ?
There remained to be answered certain important questions -to one of which we have already alluded. How long will the antiseptic virtue of this medicated timber abide in it? Will not the corrosive sublimate, essentially a poison, be disengaged from the vegetable body with which it has combined, under exposure to air and moisture ? And if this be the case, will not the wood lose its protection against the usual sources of dry rot, while, at the same time, the disengaged poison mingles with and contaminates the atmosphere breathed by the ship's crew ?
Mr. Faraday proceeded to detail a very ingenious series of chemical experiments, in which these startling doubts had led him to engage; and the issue of which, as far as they go, is satisfactory. Mr. Kyan stated that, on the contact of corrosive sublimate with any vegetable juice containing albumen, a new combination, a tertium quid, results; and upon this view Mr. Faraday experimented. He found that prepared canvas and calico, when washed in water until a certainty was obtained that that fluid would remove nothing more, still gave mercury to weak nitric acid ; the presence of a mercurial compound, proof against water, was thus, he thought, established—and he inferred that it could evolve, under ordinary circumstances of exposure, no noxious
whatever. Enough has, we hope, been said to attract the notice of distant readers, to a subject which appears to be fixing every day more firmly the attention of the scientific circles in this metropolis. Whether the process of Mr. Kyan is as yet entitled to be sanctioned by the use of government in our public establishments and whether the example of Sir Robert Smirke, who has applied timber thus medicated in various new buildings under his charge, (in the Temple for instance,) will of itself be sufficient to stimulate the researches of his professional rivals, we do not pretend to say: but shall conclude with a very few observations on the benefits, national and domestic, which could not fail to result from the discovery and general adoption of a cheap, safe, and efficacious preventive of dry rot.
As to the Royal Navy, we need but refer to the long series of our preceding articles on this subject-especially to that in No. LIX.-for lamentable details of the extent and rapidity of the injuries sustained by the King's ships during the war, in consequence of this one cause. Owing principally to the prevalence of this disease, the average duration of ship-timber cannot be estimated
at more than seven, or at most eight, years; and what may
be the gross demand of the British fleet for timber? The Royal Navy consisted on the 1st of January, 1833, of 22 First-rates
of 108 to 120 guns 31 Second-rates
78 to 84 68 Third-rates
74 to 76 22 Fourth-rates
50 to 52 101 Fifth-rates
42 to 50 95 Sixth-rates
26 to 35 with seventy-four 18-gun vessels, and one hundred and sixty-one small craft, making in all 574 armed vessels. Mr. Edye estimates the quantity of wood required for the construction of a first-rate of 120 guns at 5880 loads—for an 80-gun ship, 4339 loads—for a 74, 3600—for a 52, 2372—for a fifth-rate, 1800 loads—and for a sixth-rate, 963. According to him, therefore, it would take, to build the existing 574 ships, not much under a million loads of timber; and the quantity annually requisite to keep them seaworthy will be 125,000 loads. In what exact proportions this expense is occasioned by dry rot in seasoning, and by dry rot in ships, it is not in our power to say; but we are sure, whoever considers the detailed histories of individual vessels in our articles above referred to, in Mr. Knowles's book, and in the article Dry Rot' in the Supplement to the Encyclopædia Britannica, will be prepared not to start when he hears that, according to the opinion of some of the best judges we know, the annual saving of timber in the Royal Navy, were a real cure for dry rot discovered and adopted, would not be much under 50,000 loads.
A single and simple fact, stated in three words, will perhaps bring the matter home to the reader's imagination, as readily as any given number of calculations and estimates. The Benbow was built in 1813 ; dry rot infected her; and she was repaired in 1818, at Portsmouth, without ever having been to sea, at the expense of 45,0001.
If the new or perfected invention, of which we have been treating, should answer even to the extent which Mr. Faraday said he considered to have been already placed beyond all doubt, it is obvious that the saving to the nation would be most important. Indeed, if it should come to no more than sparing us the expense of having all our ship timber felled many years before it is used, that, on so large a stock, would be no trivial saving. But we confess, when we think of five years in the fungus pit having left neither spot nor blemish on any one of nine specimens, we are inclined to consider this as a very subordinate feature of the case. In buildings on shore, more particularly large and public ones,