of steel to exactly the same degree. A ing to the eye, but it can be produced by single test is of comparatively small hammering cold. The consumer of steel value, as a second rate quality of steel may be enraptured, if he be of a poetical may stand very well the first time of turn of mind, by the superb fracture of a hardening, but deteriorates much more bar of steel, reminding him of a picture rapidly every time it is re-hardened, than by Ruskin of the aguille structure of the is the case with high-quality steel. Nor Higher Alps; but, after all, this is only a am I at all sure that the breaking strain dodge, depending upon the inclination is a fair test of the quality of steel. For of the axis of the revolving hammer to many tools the capacity to withstand a the plane of the anvil. The practical high amount of breaking strain slowly consumer of steel must descend from the applied is not so much required as its heights of art and science, and take capacity to withstand a sudden shock. refuge in the commonplace of the rule of The appearance of the fracture is very thumb, and buy the steel which his illusory. The fineness of the grain and workmen tell him is full of "nature" and the silkiness of the gloss is very captivat- "body."

EXPERIMENTS ON THE STRENGTH AND STIFFNESS OF SMALL SPRUCE BEAMS.

By F. E. KIDDER.

From Proceedings of the American Academy of Arts and Sciences.

THE object of the following experi- the deflections at a distance of one-inch ments was to determine the Moduli of from the center; but the deflections used Elasticity and Rupture in small beams in calculating the values of the Modulus of white spruce (Abies alba); and such of Elasticity were corrected so as to give other information as might be derived the deflection at the center, supposing from the data obtained.

The machine used for the purpose consists of two solid wooden frames, carefully leveled and placed forty inches apart. Upon the top of each frame is placed a movable plate of iron, which is carefully adjusted so that the two plates shall be directly opposite each other, and exactly forty inches apart between the faces. These plates form the supports for the beams.

the curve assumed by the beam to be the arc of a circle; from which, in fact, it deviates but little under such small loads. In reading the micrometer, the principle of electrical contact was taken advantage of.

The greatest errors liable to occur in using the machine are as follows:

In measuring the deflections, one tenthousandth of an inch. In the breaking load, possibly one pound; but in the The loads were applied by means of a small loads there could be no appreciable scale pan suspended from a three-quarter error. In measuring the dimensions of inch bolt, which rested upon the center the test pieces, two thousandths of an of the beam. By means of an iron strap suspended from a horizontal beam placed above the test piece, and resting on two screws, the bolt from which the load was suspended could be raised from or lowered upon the test piece as easily and gradually as could be desired.

inch.

The experiments were conducted with the utmost care, and every possible precaution was taken to prevent errors.

In arranging for the experiments, and while making them, the writer was greatly assisted by Mr. Holman of the Institute, to whom he extends his acknowledgements.

The deflections of the beams were measured by means of a micrometer screw, reading to one ten-thousandth of The pieces of wood experimented on an inch. As the bolt from which the were sawn from a spruce plank that had load was suspended rested on the center been cut in eastern Maine in the spring of the beam, it was necessary to measure of 1880, and the following summer

Vol. XXIV.--No. 6.-33.

shipped to Boston, where it had lain in and had but few defects, and in testing the open air until it was cut up in Octo- the beams they were placed so that the ber. The pieces were carefully planed defects should have the least possible to an approximate size of one and a-half effect upon the strength of the beams. inches square and four feet long. The exact dimensions of the test pieces

They were nearly all straight-grained are given in Table I:

each piece, com-
3 WI
2 BD"

The values of the Modulus of Elas- weight would, probably, break the beam ticity calculated from these deflections if applied long enough. are also given. The Moduli of Elasticity Table I. gives the values of the obtained from the deflection of the beams Modulus of Rupture of immediately after the weight was apin which plied have been denoted by E, and puted by the formula R= those obtained from the deflection of R denotes the Modulus of Rupture; W the pieces after the weight had been the breaking weight of the beam, and applied one or more hours, by E. Table the other letters have the same signifiI. gives the values of E and E, for each piece, obtained by taking the average of the values given in Table II. The values of E were computed by in which W de

the formula E=

WI

4 ABD" notes the weight in pounds producing the deflection; the clear span in inches; ▲ the deflection of the beam at the center; B the breadth of the beam, and D the depth, both in inches.

After all the beams had been treated in this way, piece No. 3 was again put in the machine and subjected to a load of 100 lbs., which was allowed to remain upon the beam for about two hours, the deflection being measured directly after the weight was applied and just before it was removed. The beam was then allowed a certain time to recover its set. In two cases, the beams, after having been subjected to a load of 100 lbs., finally returned to their original position, and it appeared probable that all would have done so had sufficient time been allowed for the purpose.

After the piece had nearly recovered from the effects of the load of 100 lbs., a load of 150 lbs. was put on the beam, and gradually increased until the breaking point was reached.

cance as in the formula for E. The load which would break a beam of the same wood, one inch square and one foot between supports, if applied at the center, is also given in the same table. This load is one eighteenth of the Modulus of Rupture.

When the weight of 400 lbs. was applied to piece No. 7, it immediately cracked at a knarl in one of the lower edges, about three fourths of an inch from the center of the beam. As it was thought that the beam would soon break entirely, the load of 400 lbs. was allowed to remain on the beam; but at the end of one hundred hours the deflection had only increased 0.2224 inches, and as it was evident that it would, at that rate, take a long time for the beam to break, the load was then gradually increased until the piece broke at 550 lbs., giving a Modulus of Rupture considerably above the average.

It was noticed in this beam that the deflections under the loads above 500 lbs. were considerably greater than in the other beams under the same loads.

Piece No. 5 gave a very high breaking weight, and broke very suddenly, more like the harder kinds of wood. The fracture was very perfect, the upper half of the fibers being very evidently compressed and the lower half suddenly pulled apart, with almost no splintering. This piece had a small knot on the upper side, five inches from the center of the beam, but it appeared to have no effect upon the strength of the beam.

The remaining pieces were tested with a load of 100 lbs. in the same way, and then subjected to a load of 400 lbs. for one or two minutes, for the purpose of getting the deflection under that load, and immediately after subjected to the full load of 500 lbs., which was gradually increased until the piece broke. As the Piece No. 4 broke in a rather peculiar load approached the breaking weight, it manner. While under a load of 575 lbs., was increased by the addition of only the lower fibers for about a depth of one or two pounds at a time, so that the one-tenth of an inch snapped apart, and breaking weight could be obtained with the beam gradually settled down until sufficient accuracy. In fact, the break- the next layer of fibers had apparently ing weight is so much modified by the the same deflection as did the lower ones time occupied in breaking the beam, that at the time of breaking, when they also it is difficult to ascertain exactly what it snapped, making a layer of about the really is. For any load over three- same thickness. In this way the whole fourths of what is called the breaking lower half of the beam seemed to divide

itself into layers of about one-tenth of before. The beam was thus subjected an inch thick, and to break separately to a weight of 275 lbs. for three hundred under about the same deflection, so hours in all, after which it was broken in that the beam was a long time in breaking.

the same manner as the others. It was expected that the effect of such a severe strain for so long a time would diminish its strength; but, on the contrary, it appeared to increase it, as the beam gave a higher Modulus of Rupture than any of the others, although it did not appear to be of as good quality as many of them. The ultimate deflection of this beam greatly exceeded that in any of the others.

Observing that under every load that had been applied the deflection kept increasing with the length of time the weight remained on the beam, piece No. 7 was subjected to a load of 275 lbs. for ninety-eight hours, during which time the deflection increased 0.079 inches. The weight was then taken off and the beam allowed to recover for twenty-four hours, when it had a set of .0446 inches. Table III. shows the deflection of The same weight was again applied, and each beam under loads of 30, 40, 100, it was found that the deflection, obtained 400, 500, and 550 lbs., immediately after by taking the difference between the the load was applied, and at a distance readings of the micrometer just before of one inch from the center. The small and after the weight was applied, was figures under each deflection show what less than it was the first time the weight it would be if Hooke's Law held true, was applied, and the rate of increase of taking the deflection under 30 lbs. as the the deflection was about the same as starting point.

taken at from 1,600,000 to 1,700,000 lbs., and the Modulus of Rupture at about 11,000 lbs.

Modulus is consequently very nearly constant for all moderate deflections. That a high Modulus of Elasticity does not always accompany high transverse The only other experiments on Ameristrength; for, as shown by Table I., can spruce with which the writer is piece No. 10, which had the greatest familiar are those made by Mr. R. G. transverse strength, gave next to the lowest value of E.

That in spruce beams the upper fibers commence to rupture by compression under about four-fifths of the breaking weight, and the neutral axis is very near the center of the beam as shown by the fracture.

That beams which are subjected to severe strains for a long time bend more before breaking than those which are broken in a comparatively short time.

That the Modulus of Elasticity of small spruce beams, of a quality such as is used in the best buildings, may be

Hatfield on small beams, 1.6 feet between supports, and some experiments by Mr. Thomas Laslett, of England, on pieces of Canada spruce, 2 inches square and 72 inches between supports. value

Mr. Hatfield gives as the average of the transverse strength of a unit beam, 612 lbs.. which would give 11,016 lbs. for the Modulus of Rupture.

*

From data given by Laslett† we obtain as the value of R, 9,045 lbs.

The value generally given for the Modulus of Elasticity of spruce is 1,600,000 lbs.

GAS AND ELECTRICITY AS HEATING AGENTS.*
By Dr. C. WILLIAM SIEMENS, F.R.S.
From "Iron."

On the 14th of March, 1878, I had the honor of addressing you "On the Utilization of Heat and other Natural Forces." I then showed that the different forms of energy which Nature has provided for our uses had their origin, with the single exception of the tidal wave, in solar radiation; that the forces of wind and water, of heat and electricity, were attributable to this source, and that coal formed only a seeming and not a real exception to the rule-being the embodiment of a fractional portion of the solar energy of former geological ages.

wood, is practically inert to oxygen at ordinary temperatures; but if wood is heated to 295° C. (593 Fah.), or coal to 326° C. (617° Fah.) according to experiments by M. Marbach, combination takes place between the fuel and the oxygen of the atmosphere, giving rise to the phenomenon of combustion. It is not necessary to raise the whole of the combustible materials to this temperature, in order to continue the action; the very act of combustion when once commenced gives rise to a great development of heat, more than sufficient to prepare additional carbonaceous matter, and additional air for entering into combination; thus a match suffices to ignite a shaving, and that in its turn to set fire to a building.

On the present occasion I wish to confine myself to one branch only of the general subject, namely, the production of heat energy. I shall endeavor to prove that for all ordinary purposes of The first effect of combustion is, thereheating and melting gaseous fuel should fore to heat the combustible and the air be resorted to, but that for the attain- necessary to sustain combustion to the ment of extreme degrees of heat the temperature of ignition, but in dealing electric arc possesses advantages, un- with the combustible called coal other rivaled by any other known source of preparatory work has to be accomplished, heat. besides mere heating in order to sustain

Carbonaceous material such as coal or

*Hatfield's Transverse Strains, Table XLII. +Timber and Timber Trees, Native and Foreign, by A lecture delivered before the Science Lecture As- Thomas Laslett, Inspector to the Admiralty, London, sociation, Glasgow. 1875.