for which the disciples of Malpighi contend; and if the fibres and vessels of the bark really became those of the alburnum, a very great degree of similarity ought to be found in the organization of those substances. No such similarity, however, exists; and not any thing at all corresponding with the circular row of large tubes in the alburnum of the oak is discoverable in the bark of that tree. These tubes are also generated within the interior surface of the bark, which is well defined; and during their formation the vessels of the bark are distinctly visible, as different organs; and had the one been transmuted into the other, their progressive changes could not, I think, possibly have escaped my observation nor does the organization of the bark in other instances, in any degree indicate the character of the wood that is generated beneath it: the bark of the wych elm (ulmus montana) is extremely tough and fibrous; and it is often taken from branches of six or eight years old, to be used instead of cords; that of the ash (fraxinus excelsior) on the contrary, when taken from branches of the same age, breaks almost as readily in any one direction as in another, and scarcely presents a fibrous texture; yet the alburnum of these trees is not very dissimilar, and the one is often substituted for the other in the construction of agricultural instruments. Mirbel has endeavoured to account for the dissimilar organization of the bark, and of the wood into which he conceives it to be converted, by supposing that the cellular substance of the bark is always springing from the alburnum, whilst the tree is growing, and that it carries with it part of the tubular substance (tissu tubulaire) of the liber, or interior bark. These parts of the interior bark, which are thus removed from contact with the alburnum, he conceives to constitute the external bark or cortex, whilst the interior part of the liber progressively changes into alburnum. But if this theory (which I believe I have accurately stated, though I am not quite certain that I fully comprehend its author*) were well founded, the texture of the al * Chap. iii. article 5, Traité d'Anatomie et de Physiologie Végétale. burnum burnum must surely be much more intricate and interwoven than it is, and its tubes would lie less accurately parallel with each other than they do and were the fibrous substance of the bark progressively changing into alburnum, the bark must of necessity be firmly attached to the alburnum during the spring and summer by the continuity, and indeed identity of the vessels and fibres of both the substances. This, however, is not in any degree the case, and the bark is in those seasons very easily separated from the alburnum; to which it appears to be attached by a substance that is apparently rather gelatinous than fibrous or vascular: and the obvious fact, that the adhesion of the cortical vessels and fibres to each other is much more strong than the adhesion of the bark to the alburnum, affords another circumstance almost as inconsistent with the theory of Malpighi, as with that of Mirbel. Many of the experiments of Duhamel are, however, apparently favourable to the theory of Malpighi, respecting, the conversion of bark into alburnum; and Mirbel has cited two, which he appears to think conclusive*. In the first of these, Duhamel shows that pieces of silver wire, inserted in the bark of trees, were subsequently found in their alburnum; but Duhamel himself has shown, with his usual acuteness and candour, that the evidence afforded by this experiment is extremely defective; and he declares himself to be uncertain that the pieces of wire did not, at their first insertion, pass between the bark and the alburnum; in which -case they would necessarily have been covered by every successive layer of alburnum, without any transmutation of bark into that substancet. In the second experiment cited by Mirbel, Duhamel has shown that when a bud of a peach tree, with a piece of bark attached to it, is inserted in a plum stock, a layer of wood perfectly similar to that of the peach tree will be found, in the succeeding winter, beneath the inserted bark. The statement of Duhamel is perfectly correct; but the experiment does not by any means prove the conversion of bark into wood; for if it be difficult to conceive (as he remarks) that Chap. iii. article 5, Traité d'Anatomie et de Physiologie Végétale. + Physique des Arbres, liv. iv. ch. 3. an an inserted piece of bark can deposit a layer of alburnum, it is at least as difficult to conceive how the same piece of bark can be converted into a layer of alburnum of more than twice its own thickness (and the thickness of the alburnum depo→ sited frequently exceeds that of the bark in this proportion), without any perceptible diminution of its own proper substance. The probable operation of the inserted bud, which is a well-organized plant, at the period when it becomes capable of being transposed with success, appears also, in this case, to have been overlooked; for I found that when I destroyed the buds in the succeeding winter, and left the bark which belonged to them uninjured, this bark no longer possessed any power to generate alburnum. It nevertheless continued to live, though perfectly inactive, till it became covered by the successive alburnous layers of the stock; and it was found many years afterwards enclosed in the wood. It was, however, still bark, though dry and lifeless, and did not appear to have made any progress towards conversion into wood. In the course of very numerous experiments, which were made to ascertain the manner in which vessels are formed in the reproduced bark*, many circumstances came under my observation which I could adduce in support of my opinion, that bark is never transmuted into alburnum; but I do not think it necessary to trouble you with an account of them; for though much deference is certainly due to the opinions of those naturalists who have adopted the opposite theory, and to the doubts of Duhamel, I am not acquainted with a single experiment which warrants the conclusions they have drawn; and I think that were bark really transmuted into alburnum, its progressive changes could only have escaped the eyes of prejudiced or inattentive observers. In the course of the ensuing spring, I hope to address to you some observations respecting the manner in which the alburnum is generated. I am, my dear sir, Elton, Dec. 29, 1807. your most obliged obedient servant, THOMAS AND. KNIGHT. Philosophical Transactions for 1807. XXIV. Analysis XXIV. Analysis of various Kinds of Pit-Coal. By DAVID SIR, Ir has often been a matter of surprise to me that we should possess so scanty a share of knowledge on the component. parts of pit-coal, or at least that so small a share of that knowledge should meet the public eye. Except the analysis given by Mr. Kirwan, I do not recollect any in our language. After this short preface, I shall offer no apology for sending you the details that follow. Welsh Furnace Coal from Cyfartha. The appearance of this coal is deep shining jetty black, possessed of an irregular crystallized fracture, rather inclining to soft and friable. Specific gravity 1.337. 340 grains of this coal, in small pieces, were introduced into a close fitted iron retort. It continued longer in the fire without inflaming than the common sort of English or Scotch coals, and afterwards burnt with a small quantity of lightcoloured bituminous flame. Upon examining the result, I found the pieces welded, though not run into one common. mass; the exposed angles were all rounded, but no great degree of adhesion had taken place. The coke thus obtained was of a dark-gray silvery colour, very sonorous, and weighed 311 grains. Loss 29 grains. Volatile matter lost in a heat nearly white 8.5 91.5 100 parts. 100 grains of this coke were reduced to a fine powder, and exposed in an iron capsule heated to redness in contact with the external air. After the complete combustion of the carbonaceous matter, a grayish-red ash was found weighing 3:75 grains: the coke is therefore composed of carbon 96.25, ashes 3.75, 100 parts. And 100 parts of this coal will be composed as follows: Volatile Alfreton Furnace Coal. The appearance of this coal is glossy black, composed of alternate layers of soft coal and black, charry, carbonaceous matter, with now and then thin lamine of hard coal. Cross fracture of the beds somewhat shining and pitchy. Specific gravity 1.235. Distilled under the same circumstances as the Welsh coal, the results were as follow: Small pieces of coal weighing 300 grains 163 The fracture of this coke was more cellular than that of the Welsh, and the mass more united and compact; the colour a lighter gray. 100 parts of the coke was found composed of carbon 96-25, ashes of a light-brown colour 3.75, 100 parts. 100 parts of the same coal were composed of Bituminous matter and water 45.500 Carbon Ashes 52.456 2.044 100 parts. Butterly Furnace Coal. Strong hard coal, colour dull sooty black, fracture sharp and uneven. Specific gravity 1.264. 300 grains of it distilled, yielded 171 grains of a lightcoloured gray silvery coke. The pieces were nearly of the same |