In a lecture delivered by John Anderson, C. E., at the “ So, ciety of Arts” in London, some information was given on the contraction of timber which we deem of sufficient interest to reproduce from The ErnYdcr, together with the diagrams illuStrative of the subject. The lecturer, after some introductory remarks proceeded as follows : The wretched state of the floors, doors, and shutters in many of the London houses too plainly gives ample and complete evidence of per si stent disobedience to the natural law of shrinkage, and the only hopeful consolation is that we do not go unpunished, as the. penalty inflicted in time may lead to impro ve ment. An examination of the end section of any exogenous tree, such as the beech or oak will show the general arrangement of its structure. It consists of a mass of longitudinal fibrous tubes, arran ged in irregular circles that a re bound together by means of radial strings or shoots, which have been variously named ; they are the “ silver grains “ of the carpenter, or the “ medullary rays “ of the botanist, and are in reality, the same as end wood, and have to be considered as such, just as much as the longitudinal woody fiber, in order to understand its action. From this it will be seen that the lateral contraction or collap sing of the longitudinal, porous, or tubular part of the structure, cannot take place without first crushing the m edullary rays, hence the effect of the shrinking finds relief by splittin g in another direction, namely in radial lines from the cent er, parallel w ith the m edullary rays, thereby enabling the tree to maintain its full diameter, as shown in Fig. 1. If the entire mass of tubular fibercompo sing the tree were to contract bodily, then the medullary rays would of necessity have to be crushed in the radial direction to enabl e it t o take place, and the ber would thus be much injured in proportion as would be the case in crushing the wood in the longitudinal direction. If such an oak or beech tree is cut into four quarters, by passing the saw twice through the center at right angles, before the contracting and splitting have commenced, the lines a c, and c b, in Fig. 2 would be of the same length, and at right angles to each other,or, in the technical language of the workshop, they would be sq liare ; but, after being stored in a dry place, say for a year, it would then be seen that a great change had taken place both in the form and in some of the dimensions ; the lines c a, c b, would be the samel ength as before, but it would have contracted from a to b very considerably, and the two lines c a, and c b, would not be at right angles to each other by the portion here shown in white in Fig. 3. The medullary rays are thus brought closer by the collapsing of the vertical fiber. But, supposing that six parallel saw cuts are passec through the tree so af to form it into seven planks, as shown in Fig. 4, let us see what would be the. behavior of the several planks. Take the center plank first. After due seasoning and contracting, h would then be found1 that the middle of the board would still retain the original thickness, from the resistance of the medullary rays, while it would be gradually reduced in thickness toward the edges for want of support, and the entire breadth of the pl ank would be the same as it was at first, for the foregoing reasons, and as shown in Fig. 5. Then, t ak in g the planks at. each side of th e center, by the :lame law their change and behavior would be quite different ; they would still retain their original thickness at the center, but would be a little itducea on eacn edge throughout, but the side next, to the heart of the tree would be pulled round or partly cylinirical, while the outside hollow, and the plank would be considerably narrower throughout iu entire leng th, more especially on the face of the hollow side, all dut to the want of support. Selecting the next two planks, they would be found t o have lost non e of their[thickness at the center, and very little of their thickn3ss at the edges, but very much of would be the reverse, or their breadth as planks, and would be curved round on the heart side, and made hollow on the outside. S upposing some of these planks, to be cut up into squares when in the green state, the shape that these squares would assume, after a period of seasoning, would entirely depend on the part ofthe tree t o which they belonge d; the great e st alteration would be parallel with the medullary rays. Thus if the square was near the outside, the e ffe c t woul1 be as sh own in Fig. 6, namely, to contract in the direction from a tob, and after a year or two it would be thus, as seen in Fig. 7, the distance between c and a being nearly the same as they were before, but the other two are brought by the amount of their contraction closer together. By understanding this natural law, it is comparatively easy to know the future behavior of a board or plank by carefully examining the end of the wood, in order to ascertain the part of the log from which it has been cut, as the angle of the ring growths and th e m e d ull ary rays will show thus, as in Fig. 8. If a plank has this appearance, it will evidently show to have been cut from the out- side,andfor many years it will gradually shrink the iv xt plank, shown in Fig. 9, clearly points close to the center or heart of the tree, where it will not shrink to the breadth but to a varying thickness, with the full dimensions in the middle, but tapering to the edges, and the planks on the right and left will give a mean, but with the center sides curved round, and the outside still more hollow. The fore going remarks apply more especially to the stronger exogenous woods, such as beech, oak, and the stronger home firs. The softer woods, such as yellow pine, are governed by the same law, but in virtue of their softness another law comes into force, which to some degree affects their behavior, as the contracting power of the tubular wood has sufficient strength to crush the ,softer. medullary rays to some extent, and hence the primary law is so far modified. But even with the softer woods, such as are commonly used in the construction of houses, if the law is carefully obeyed, the greater part of the shrinking, which we are all too familiar with, would be obviated, as the following anecdote will serve to show: It was resolved to build four houses, all of the test class, but one of the four to be pre-eminently good, as the futtire residence of the proprietor. The timber was purchased for the entire lot, and the best portions were selected for house No. 1, but by one who did not know the law, and t o make certain of success this portion of the wood had an extra t welve months' seasoning after it was cut up. The remainder of the wood was then . handed over to a contractor for the other three houses, who han an intelligent young foreman, who knew the structure of wood as well as how to obey the law, and who, therefore- had the wood for the three houses cut up in accordance therewith. The fourth house was built the following year by another man; but long before ten years had passed to the great surprise and annoyance of the proprietor, it was found that his extra good house, No. 1, had gone in the usual manner, while the other three houses were without a shrinkage from top to bottom. As Solomon says, “ Wisdom is profitable to direct." A similar want of correct knowledge of the natural figure and properties of the structure of wood, such as the oak, is con stantly shown by the imperfe ct painting to resemble that wood, as exhibited on the doors and shutters of m any of the houses of this metropolis. If we cannot afford to have genuine wainscot doors, 3S in France, but yet desire to have an imitation, it would surely be worth the trouble to have a block cut from the quarter of an oak tree, and to have each of its six sides planed and polished, in order to make plain their several features. The house painter would then see what nature really is, and thus save us from the ridicule of other nations, when we mix up “ silver grains “ and all the other natural features upon one side of a board or panel. On Cotton-seed Oil, and its Detection when mixed witli other Oils. Mr. Reynolds believes that nearly th e whole of c otton- seed oil is used in the sophistication of oils of older repute. The probability that the supply will now continue and increase is especially indicated by a consideration of the source of the oil. The w eight of seed yielded by each cotton plant Is about three times as great as the cotton obtained from it, and up to the present time nearly the whole of this seed has been wasted, or returned to the soil as a fertilizer. The present price of the refined oil is less than three shillings per gallon, and, considering the large porportion of seed that has yet to be utilized, it is probable that it will long continue to be the cheapest fixed oil in the market. Hence the desirability °f our giving some attention to a sub stan c e which is pretty sure to present itself to us in oar daily avocations in some shape or other. After describing the methods of preparing- and puiifymg cotton-seed oil, Mr. Reynolds adds some remarks upon the detection of this oil when mixed with olive oil. A well-known chemist, whom he regarded as the highest authority upon the subject of the adulteration of oils, told him that lie did not know of a test for this purpose. The experime l)ts which he made induced him to regard the nitrate of mercury test as affording sufficiently clear ro actions to enable him to fiDd this oil when mixed with, olive oil. He used Pontet's test as follows : 6 parts of mercury are dissolved in parts, by weight, of nitric acid, 1'36 without the application of heat, and form the test solution. The tubes ' for making these experiments are merely strong test; tubes of 7 inches in length, and holding about a fluid ounce. They are r0U ghly graduated by po uring in 30 minims of water and Bcratchin g a line upon the glass ; another line is made. at the p0int reached when a total of 6 drachms of water have been poured in. The lower line is marked “ test,” the upper one “ oil.” Pour in first the test to its mark, and fill up with the suspected oil to the other line; shake well and set aside, shaking again about an hour afterwards. In from three to twelve hours, according to the temperature, etc., a genuine olive oil will have solidified entirely, the product after the latter interval being quite hard when touched by a glass rod. Cotton-seed oil, when similarly treated, will not solidify, but remains fluid. A mixture of 25 parts of cotton-seed oil with 75 parts of olive oil gives an intermediate condition. The contents of the tube become solid, but if a little be taken out with a glass rod, it is found to be soft, pasty, and without any friable character. On the other hand, when pure olive oil is so treated. the product is hard, friable, and.n°t pasty. C0mparative trials should always be made, and caution exercised in accepting the apparent conclusions. Where only 12t per cent of cotton-seed oil is present, the reactions are not so distinct as with 25 per cent., but Mr. Reynolds! ^nad^s them usually sufficient to decide the cas^.-Druggists' Circular.
This article was originally published with the title "The Contraction or Shrinking of Timber"