change in temperature of 1° Centigrade, is termed the coefficient of linear expansion, for the material in question.

The increase in length for other changes of temperature than 1° is given by the following formula:

1 = KNL,

in which L is the length at 0° C.; N, the number of degrees above 0°; K, the coefficient of linear expansion; and the increase of length due to N degrees above 0° C.

Table of Coefficients of Linear Expansion for 1° C.

It has been found from experiment that the absorption of water in any manner decreases the coefficient of linear expansion in wood; and that, in some cases, in stone it increases this coefficient, whilst in others a permanent increase of length took place from an increase of temperature.

An increase in temperature of 15° C. in cast iron, and 8°

C. in wrought iron will produce a strain of one ton of 2240 lbs. on the square inch, when the two ends of the bar abut against a fixed object.

XI.

ADHESION OF IRON SPIKES TO TIMBER.

380. THE following tables and results are taken from an article by Professor Walter R. Johnson, published in the Journal of the Franklin Institute, Vol. 19, 1837, giving the details of experiments made by him on spikes of various forms driven into different kinds of timber.

The first series of experiments was made with Burden's plain square spike, the flanched, grooved, and swell spike, and the grooved and swelled spike. The timber was seasoned Jersey yellow pine, and seasoned white oak.

From these experiments it results, that the grooved and swelled form is about 5 per cent. less advantageous than the plain, in yellow pine, and about 18 per cent. superior to the plain in oak. The advantage of seasoned oak over the seasoned pine, for retaining plain spikes, is as 1 to 1.9, and for grooved spikes as 1 to 2.37.

The second series of experiments, in which the timber was soaked in water after the spikes were driven, gave the following results :

For swelled and grooved spikes, the order of retentiveness was: 1 locust; 2 white oak; 3 hemlock; 4 unseasoned chestnut; 5 yellow pine.

For grooved spike without swell, the like order is: 1 unseasoned chestnut; 2 yellow pine; 3 hemlock.

The swelled and grooved spike was, in all cases, found to be inferior to the same spike with the swell filed off.

The third series of experiments gave the following results: Thoroughly seasoned oak is twice, and thoroughly seasoned locust 2 times as retentive as unseasoned chestnut.

The forces required to extract spikes are more nearly proportional to the breadths than to either the thickness or the weights of the spikes. And, in some cases, a diminution of thickness with the same breadth of spike afforded a gain in

retentiveness.

ADHESION OF IRON SPIKES TO TIMBER.

171

"In the softer and more spongy kinds of wood the fibres, instead of being forced back longitudinally and condensed upon themselves, are, by driving a thick, and especially a rather obtusely-pointed spike, folded in masses backward and downward so as to leave, in certain parts, the faces of the grain of the timber in contact with the surface of the metal."

"Hence it appears to be necessary, in order to obtain the greatest effect, that the fibres of the wood should press the faces as nearly as possible in their longitudinal direction, and with equal intensities throughout the whole length of the spike."

The following is the order of superiority of the spikes from that of the ratio of their weights and extracting forces respectively :—

"All the experiments prove, that when a spike is once started the force required for its final extraction is much less than that which produced the first movement."

"When a bar of iron is spiked upon wood, if the spike be driven until the bar compresses the wood to a great degree, the recoil of the latter may become so great as to start back the spike for a short distance after the last blow has been given."

342. From the fourth series of experiments it appears, that the spike tapering gradually towards the cutting edge gives better results than those with more obtuse ends.

That beyond a certain limit the ratio of the weight of the spike to the extracting force begins to diminish; "showing that it would be more economical to increase the number rather than the length of the spikes for producing a given effect."

"That the absolute retaining power of unseasoned chestnut on square or flat spikes of from two to four inches in length is a little more than 800 lbs. for every square inch of their two faces which condense longitudinally the fibres of the timber."

CHAPTER III.

MASONRY.

I. CLASSIFICATION OF. II. CUT STONE MASONRY. III. RUBBLE-STONE MASONRY. IV. BRICK MASONRY. V. FOUNDATIONS OF STRUCTURES ON LAND. VI. FOUNDATIONS OF STRUCTURES IN WATER. VII. CONSTRUCTION OF MASONRY.

SUMMARY.

I.

CLASSIFICATION OF MASONRY.

Masonry defined and classified (Art. 381).

Definitions (Art. 383). (Arts. 391-392).

II.

CUT STONE MASONRY.

Requisites of Strength (Arts. 384-390). Bonds Cutting (Art. 393).

III.

RUBBLE-STONE MASONRY.

Quality (Art. 394). Construction (Arts. 395–397).

IV.

BRICK MASONRY.

Construction (Arts. 398-402). Concrete Walls (Arts. 403-416).