Part 2

A small jet of high pressure water, injected into a larger jet from the water works mains, intensified the pressure of the latter in the delivery hose, and also increased the quantity. By this means a jet of great power could be obtained at the top of the highest building without the intervention of fire engines. This apparatus enabled the hydraulic power supply to act as a continuous fire engine wherever the mains were laid, and was capable of rendering the greatest assistance in the extinction of fire; but there was an apathy on the subject of its use difficult to understand. In Hull the corporation had put down a number of these hydrants in High Street, where the hydraulic power mains were laid, and they had been used with great success at a fire in that street. The number of machines under contract to be supplied with power was sufficient, with a suitable reserve, to absorb the full capacity of the station at Falcon Wharf, and another station of about equal capacity was now in course of erection at Millbank Street, Westminster. The works had been carried out jointly by the author and Mr. Corbet Woodall, M. Inst. C. E.; Mr. G. Cochrane had been resident engineer and superintendent. The pumping engines, accumulators, valves, etc., and a considerable portion of the consumers' machinery, had been constructed at the Hydraulic Engineering Works, Chester. Sir James Allport, Assoc. Inst. C. E., who was the first to adopt hydraulic power for railway work, had been associated with the enterprise from the commencement of its operations in 1882. His wide influence and extended experience had greatly assisted the commercial development of the undertaking.

TEST OF A WROUGHT IRON DOUBLE TRACK FLOOR BEAM.[1]

By ALFRED P. BOLLER, Mem. Am. Soc. C. E.

Testing to rupture actual bridge members is always a matter of great scientific interest, and while the record is quite extensive in eye bars, posts, or small parts, the great cost, time, and inconvenience of handling heavy girders has prevented experiment in that direction. In fact, the writer is unaware of any experiment upon compound riveted beams on a large scale, as actually used, until the experiment recorded below was made under his supervision. The beam was an exact duplicate of those in use on a bridge, about which more or less controversy had arisen as to their practical safety, and the test was made under, as near as possible, actual conditions of attachment and loading. The annexed drawing shows the form and proportion of the beam and connection with the posts, together with the position of the track stringers. The actual static loads to which the beam could be subjected by the heaviest engines in use on the road, with weight of floor, is 40,000 lb. at each stringer bearing, the strains computed therefrom being as follows: Flange strains at _m_, 3,800 lb. per square inch; at _a_, 5,700 lb. per square inch; at _b_, 6,400 lb. per square inch. Shear strains in web, between _a_ and _b_, 2,600 lb. per square inch. Shear strains in web, between _a_ and end, 8,000 lb. per square inch at least section, or where the web is 2 feet 4 inches deep, or 42 diameters between angle iron.

[1] Abstract of a paper read before the American Society of Civil Engineers, November 16, 1887.

_Rivets._--All rivets 7/8 inch diameter, or 15/26 inch when driven to fill holes; area of section, 0.6 square inch; bearing area, diameter × 3/8 plate = 0.35 square inch, and for 1/2 inch plate 0.47 square inch. Post attachment, considering all the twenty-six rivets doing duty, yields rivet strain as follows: In shear, single 5,000 lb. per square inch: and bearing area--1/2 inch plate--6,600 lb. per square inch.

_Connection of 3/8 Web to Flange Angles._--Taking the forty rivets between ends of girder and second stringer, the horizontal strain difference is 162,000 lb., the rivets being strained 3,400 lb. per square inch double shear, and 11,600 lb. per square inch bearing area. Taking distance from ends to first stringer, the horizontal strain difference is 105,000 lb., yielding on twenty rivets 4,200 lb. per square inch double shear, and 15,000 lb. per square inch bearing area. Taking a short distance of 2 feet from ends, the horizontal strain is 70,000 lb. on ten rivets, giving 5,800 lb. per square inch double shear, and 20,000 lb. per square inch bearing area. In these girders the weakness feared was in the end flange riveting and shear in end web, and caused the test recorded below. The test was recently made at the works of the Keystone Bridge Company, by means of hydraulic power applied at stringer points. Convenience made it necessary to make the test with the beam blocked up horizontal on the ground, so that the weight of the beam is necessarily neglected. The beam was connected with a pair of posts, precisely as in the actual structure, between which an additional girder was framed as a reaction base for the rams. The annexed diagram shows the general arrangements. The hydraulic power was derived from the testing machine plant of the Keystone establishment, and the deflections measured from a fine wire parallel to the lower flange, and about 3 inches therefrom. The diameter of the ram was 10 inches; area 78.54 inches. The record was as follows:

Gauge Load on Deflections. Total reading. each ram. _b_ _b_' load. lb. in. in. lb.

565 44,375 1/8 1/8 177,500 1130 88,750 5/16 5/16 355,000 1412 110,900 3/8 3/8 443,600 No permanent set in above 1695 133,125 uncertain. -- -- 532,500 Permanent set scant 1/32 inch. 1980 155,500 not recorded. -- -- 622,000 Permanent set 5/32 inch. 2080 Failure commenced. -- -- 653,500

Failure commenced through giving way of angle irons, beginning in a fine seam in the first bend of the lower flange from the end support, the seam being along the root of the angle, which continual pressure tore apart across the angle as shown, when the web commenced to tear like a sheet of paper, in direction and manner as exhibited on plate herewith--from photograph. From some cause not apparent the deflections were not similar at the symmetrical end rams, _a_, the point where the web failed--left side--being sharply deflected. While the angles showed root fracture at the opposite point, the web did not fail or show indications of so doing, the deflection being on an easy curve. With the extreme yielding of the lower flange angles, the angle brackets connecting girder with posts commenced to go, tearing likewise along the root, and stripping the heads from the extreme upper rivets as shown. The internal diaphragm connecting the channel sides of the posts was unaffected. The rivets connecting the ruptured flange with web appeared as perfect as when driven, and no indication was disclosed, as far as it was possible to tell, of the holes in the web elongating or any upsetting of bearing surface. There is no telling what the web and rivets would have borne had not the solid angle irons given way at the first bend. It is to be noted that flange plate with leg of angle attached thereto was intact, showing no indication of rupture.

_Discussion._--Taking that stage of the experiment when a permanent set was first noted--viz., 1/32 inch--the recorded load was 532,500 lb., or as near as may be 3-1/3 times the basis on which the calculations in the first part of this paper were made--40,000 lb. on each stringer, or 160,000 lb. total. Applying this ratio to the preceding computations, the iron would be apparently strained as follows:

{ _m_ 3,800 × 3-1/3 = 12,600 lb. per square inch (psi). Flanges at { _a_ 5,700 × 3-1/3 = 19,000 psi. { _b_ 6,400 × 3-1/3 = 21,200 psi.

Web. { Between _a_ and _b_, 2,600 × 3-1/3 = 8,700 lb. per square inch. { At least section, 8,000 × 3-1/3 = 26,600 psi.

{ Post attachment: { Bearing area, 6,600 × 3-1/3 = 22,000 lb. per square inch. { Single shear, 5,000 × 3-1/3 = 16,600 psi. Rivets. { Web and flange connections, end rivets: { Bearing area, 20,000 × 3-1/3 = 66,600 psi. { Double shear, 5,800 × 3-1/3 = 19,300 psi.

When failure in angles was first noted, the recorded load was 653,500 lb., or slightly more than four times the computed basis of load, which would increase the above strains about one-fifth, giving a calculated flange strain when angle failed of some 15,000 lb. per square inch, and bearing area strain on end flange and web rivets about 80,000 lb. per square inch, neither of which could possibly be true, or the web would have torn out from the rivets, and the flanges be perfectly sound, well within elastic limits, although in the last case it is to be noted that the horizontal table of the flange was perfectly sound, the flange failure commencing primarily with a long split along the weld of the angle iron root, throwing the whole flange duty upon the vertical legs of the angle iron, when a rupture strain was quickly reached. Had the angles been rolled from a solid ingot, or on the German method of developing from a flat instead of from the ordinary welded pile, the strength of this beam would have been largely increased. The prime weakness in this beam was due, therefore, to the mode of manufacturing the angle irons, which were weak along the weld at the root. This was also shown in the end bracket angles uniting the beam to the posts. The writer deduces from this experiment that a plate web is an exceedingly stiff member, much stiffer than is commonly supposed; that the customary method of proportioning rivets--viz., the horizontal component between any two given points divided by allowable bearing pressure per square inch equals number of rivets required--is not true, and that the friction due to power riveting has enormous value. This beam was reported to the company interested as practically safe by the writer, on general considerations, before the experiment was made, and the opinion reaffirmed after the experiment.

* * * * *

London Bridge cost $10,000,000. It is 900 feet long and 54 feet wide. 100,000 persons pass over it every twenty-four hours. The lamp posts are made from cannon taken during the Peninsular War.

HYDRAULIC TUBE PRESS.

Forming metal tubes from circular plates by pressing or forcing them, by the aid of mandrels, through dies or annular rings, though comparatively a modern manufacture, is carried on to a considerable extent, and with the improvements that are almost daily being made in it, and the rapidly extending use of such tubes, this extraordinary process bids fair to become a most important manufacture.

The press illustrated here was designed and made by Messrs. Henry Bessemer & Co., of Sheffield, for Mr. Samuel Walker, of Birmingham, for the manufacture of tubes of large size, and also for making hollow steel projectiles.

The press is made entirely of Bessemer steel, and is of the three-column construction, a strong casting of triangular form serving as a base of the press; into this casting the three columns fit, and carry on their upper ends a like casting, forming a top or entablature. Into this top casting the main cylinder is fixed mouth downward, concentric with the machine. Two small cylinders for giving the return or upward stroke rest mouth upward in the bottom casting at opposite sides. The two rams of these cylinders pass through the ends of, and carry, a crosshead, upon which the main ram rests. The two lifting rams are made long enough to pass through holes in the top casting, and thus form guides to the crosshead and mandrel.

The main ram is 24 in. in diameter, and has a stroke of 12 ft. The press is worked at a pressure of 3 tons per square inch, giving a down force of 1,300 tons. The two lifting rams are each 8½ in. in diameter, and give an upward force of 300 tons. This large upward force is required for stripping the tubes off the mandrels, in addition to raising the main ram crosshead, etc.

Referring to the engraving, the main cylinder is seen at the top with the main ram carrying the crosshead, to which are connected the two lifting rams, the cylinders for which extend below ground. By this arrangement a reciprocating motion is obtained, rams only being used, the central ram giving the downward thrust, and the two smaller side rams giving the upward stroke.

Mr. Walker has this press in operation, and from a disk of steel 3 ft. in diameter, having a mean thickness of about 4 in., he has raised a tube or cylinder with a solid end to it 3 ft. 6 in. long and 12 in. in diameter, of a uniform thickness of about 1 in., and sanguine hopes are entertained of producing greater results. Messrs. Bessemer & Co. are now making a larger press of similar construction.--_Engineering._

TIMBER, AND SOME OF ITS DISEASES.[2] By H. MARSHALL WARD.

VI.

If we turn our attention for a moment to the illustrations in the first article, it will be remembered that our typical log of timber was clothed in a sort of jacket termed the cortex, the outer parts of which constitute what is generally known as the bark. This cortical covering is separated from the wood proper by the cambium, and I pointed out that the cells produced by divisions on the outside of the cambium cylinder are employed to add to the cortex.

[2] Continued from SUPPLEMENT, No. 644, page 10281.

Now this cortical jacket is a very complicated structure, since it not only consists of numerous elements, differing in different trees, but it also undergoes some very curious changes as the plant grows up into a tree. It is beyond the purpose of these articles to enter in detail into these anatomical matters, however; and I must refer the reader to special text books for them, simply contenting myself here with general truths which will serve to render clearer certain statements which are to follow.

It is possible to make two generalizations, which apply not only to the illustration (Fig. 20) here selected, but also to most of our timber trees. In the first place, the cortical jacket, taken as a whole, consists not of rigid lignified elements, such as the tracheids and fibers of the wood, but of thin-walled, soft, elastic elements of various kinds, which are easily compressed or displaced, and for the most part easily killed or injured--I say for the most part easily injured, because, as we shall see immediately, a reservation must be made in favor of the outermost tissue, or cork and bark proper, which is by no means so easily destroyed, and acts as a protection to the rest.

The second generalization is, that since the cambium adds new elements to the cortex on the inside of the latter, and since the cambium cylinder as a whole is traveling radially outward--_i.e._, further from the pith--each year, as follows from its mode of adding the new annual rings of wood on to the exterior of the older ones, it is clear that the cortical jacket as a whole must suffer distention from within, and tend to become too small for the enlarging cylinder of rigid wood and growing cambium combined. Indeed, it is not difficult to see that unless certain provisions are made for keeping up the continuity of the cortical tissues, they must give way under the pressure from within. As we shall see, such a catastrophe is in part prevented by a very peculiar and efficient process.

Before we can understand this, however, we must take a glance at the structural characters of the whole of this jacket (Fig. 20). While the branch or stem is still young, it may be conveniently considered as consisting of three chief parts.

(1) On the outside is a thin layer of flat, tabular cork cells (Fig. 20, C_o_), which increase in number by the activity of certain layers of cells along a plane parallel to the surface of the stem or branch. These cells (C.C_a_) behave very much like the proper cambium, only the cells divided off from them do not undergo the profound changes suffered by those which are to become elements of the wood and inner cortex. The cells formed on the outside of the line C.C_a_ in fact simply become cork cells; while those formed on the inside of the line C.C_a_ become living cells (C_l_) very like those I am now going to describe.

(2) Inside this cork-forming layer is a mass of soft, thin-walled "juicy" cells, _pa_, which are all living, and most of which contain granules of chlorophyl, and thus give the green color to the young cortex--a color which becomes toned down to various shades of olive, gray, brown, etc., as the layers of cork increase with the age of the part. It is because the corky layers are becoming thicker that the twig passes from green to gray or brown as it grows older. Now, these green living cells of the cortex are very important for our purpose, because, since they contain much food material and soft juicy contents of just the kind to nourish a parasitic fungus, we shall find that, whenever they are exposed by injury, etc., they constitute an important place of weakness--nay, more, various fungi are adapted in most peculiar ways to get at them. Since these cells are for the most part living, and capable of dividing, also, we have to consider the part they play in increasing the extent of the cortex.

(3) The third of the partly natural, partly arbitrary portions into which we are dividing the cortical jacket is found between the green, succulent cells (_pa_) of the cortex proper (which we have just been considering) and the proper cambium, C_a_, and it may be regarded as entirely formed directly from the cambium cells. These latter, developed in smaller numbers on the outside, toward the cortex, than on the inside, toward the wood, undergo somewhat similar changes in shape to those which go to add to the wood, but they show the important differences that their walls remain unlignified, and for the most part very thin and yielding, and retain their living contents. For the rest, we may neglect details and refer to the illustration for further particulars. The tissue in question is marked by S, _c_, _hb_ in the figure, and is called _phloem_ or bast.

A word or two as to the functions of the cortex, though the subject properly demands much longer discussion. It may be looked upon as especially the part through which the valuable substances formed in the leaves are passing in various directions to be used where they are wanted. When we reflect that these substances are the foods from which everything in the tree--new cambium, new roots, buds, flowers, and fruit, etc.--are to be constructed, it becomes clear that if any enemy settles in the cortex and robs it of these substances, it reduces not only the general powers of the tree, but also--and this is the point which especially interests us now--its timber-producing capacity. In the same way, anything which cuts or injures the continuity of the cortical layers results in diverting the nutritive substances into other channels. A very large class of phenomena can be explained if these points are understood, which would be mysterious, or at least obscure, otherwise.

Having now sketched the condition of this cortical jacket when the branch or stem is still young, it will be easy to see broadly what occurs as it thickens with age.

In the first place, it is clear that the continuous sheet of cork (C_o_) must first be extended, and finally ruptured, by the pressure exerted from within. It is true, this layer is very elastic and extensible, and impervious to water or nearly so--in fact, it is a thin layer or skin, with properties like those of a bottle cork--but even it must give way as the cylinder goes on expanding, and it cracks and peels off. This would expose the delicate tissues below, if it were not for the fact that another layer of cork has by this time begun to form below the one which is ruptured: a cork-forming layer arises along the line [phi] and busily produces another sheet of this protective tissue in a plane more or less exactly parallel with the one which is becoming cracked. This new cork-forming tissue behaves as before: the outer cells become cork, the inner ones add to the green succulent parenchyma cells (_pa_). As years go on, and this layer in its turn splits and peels, others are formed further inward, and if it is remembered that a layer of cork is particularly impervious to water and air, it is easy to understand that each successive sheet of cork cuts off all the tissues on its exterior from participation in the life processes of the plant: consequently we have a gradually increasing _bark_ proper, formed of the accumulated cork layers and other dead tissues.

A great number of interesting points, important in their proper connections, must be passed over here. Some of these refer to the anatomy of the various "barks"--the word "bark" being commonly used in commerce to mean the whole of the cortical jacket--the places of origin of the cork layer, and the way in which the true bark peels off: those further interested here may compare the plane, the birch, the Scotch pine, and the elm, for instance, with the oak. Other facts have reference to the chemical and other substances found in the cells of the cortex, and which make "barks" of value commercially. I need only quote the alkaloids in cinchona, the fibers in the malveceæ, the tannin in the oaks, the coloring matter in _Garcinia_ (gamboge), the gutta percha from _Isonandra_, the ethereal oil of cinnamon, as a few examples in this connection, since our immediate subject does not admit of a detailed treatment of these extremely interesting matters.