Chapter XIII: TECHNOLOGY.--Future Prospects for Gas Companies.--By Mr (1)

THOS. WOOD.--Fuel and oil gas and the future Utopia of improved
gas manufacturing.--The ideal gas company of after days.--A
valuable and suggestive paper. 10349

Advertisements. 10358

THE ONE HUNDRED AND TWENTY TON SHEARS OF THE PORT OF MARSEILLES.

For a quarter of a century maritime nations have been continuously engaged in improving the mechanical appliances of their large ports. The use of tracks to bring goods to be placed on vessels as near as possible to the shipping point, the substitution of oblique moles for perpendicular ones in large docks, the creation of a hydraulic method of loading and unloading through movable cranes (which will perhaps in a near future cede to an electrical one), constitute the means most used for expediting transshipments and reducing the expense of them to a minimum. But, at the same time that the facilities for all kinds for handling packages have been increased, it has also become necessary to greatly increase the power of the machines applied to them. The construction of large packets now requires the putting in place of boilers of great weight, and the adoption of the huge pieces that compose the artillery of ironclads necessitates the use of force that has been unknown up to recent times.

At present, then, we could no longer be content with manual power, acting upon windlasses or capstans, for lifting and shifting. It has become necessary to apply steam or hydraulic motors to these operations. Of these, the latter are the most used, on account of their easy operation and their submitting to the greatest stresses with a very satisfactory proportionality of the expenditure of motive power. One of the most remarkable of such apparatus is the one that the Compagnie de Fives-Lille has recently set up on one of the moles of the national dock at Marseilles, for the service of the chamber of commerce, and this merits a description so much the more in that it is an important improvement upon the analogous apparatus now in use in other ports.

According to the conditions of the programme, powers of 25, 75, and 120 tons had to be obtained at will, with a proportional output of water, and the load had to be lifted 22 ft. above the quay and carried horizontally from 28 ft. beyond the edge to 16 ft. in the rear, so that the load might be taken from a ship and deposited upon a wagon, and _vice versa_. The shears, then, had to be capable of performing two operations, viz., of lifting the load and of carrying it horizontally. To facilitate the description, we shall first make known the arrangements that assure the second operation.

The apparatus is of the type known as oscillating tripod. The tripod consists of two lateral iron plate uprights, A A (Fig. 1), resting upon the wharf wall, and of a beam, B, jointed to them above and connected below with the head of the piston of a hydraulic press. This latter rests upon an iron plate frame, solidly bolted to masonry. The piston pulls the beam, B, toward it when it descends, and carries along in the same motion the shears, A, as well as the load suspended from their point of junction, and the load is thus carried to a distance of 16 ft. from the edge of the wharf in order to be placed upon a wagon. Conversely, if the piston rises, it pushes before it the entire framework, as well as the lifting apparatus, the hook of which travels 28 ft. beyond the edge of the wharf.

The lifting apparatus consists likewise of a hydraulic press suspended from the summit of the tripod; but, in order to prevent the joints of the cylinder from working under the action of the load, which would tend to open them and cause leakages, it is not suspended from the very axis of the junction of the shears. The cylinder rests directly upon a huge stirrup 45 ft. in length, the arms alone of which are affixed to the axis, through a Cardan joint. Under such circumstances, the stress of the load carried by the piston rod is exerted solely upon the branches of the stirrup, and the sides of the cylinder work only under the pressure of the motive water. The latter is introduced at the base of the press, through a valve that a special workman, standing upon a platform supported by the stirrup, maneuvers at will.

It will be seen that the general principle applied for utilizing the motive power is that of direct action. It has already been employed in a few analogous apparatus constructed by Sir William Armstrong, especially those of the arsenal of Spezia and of the Elswick cannon foundry, but solely for the lifting press. This is the first time that use has been made of it to effect the oscillating motion corresponding to the horizontal shifting of the load. This was formerly done through the intermedium of a mechanism that, aside from its complication and higher cost, presented the inconvenience of absorbing a large quantity of force in friction; besides, the direct action permits of performing the maneuvers much more quickly by the use of the water in reserve contained in the accumulators.

Another important improvement, likewise due to the Compagnie Fives-Lille, consists in the addition of safety clicks, which engage with racks parallel with the piston rod of each of the presses and movable with it. The clicks, on the contrary, are jointed to axes fixed on the bottom of the cylinders. This arrangement presents the following advantages: If a leakage occurs in the joints or feed pipe of the hoisting press, the descent of the load can be stopped instantaneously, thus preventing the grave damage that would be done to ships and even to the shears themselves by the descent of a 120 ton load, however slow it might be. As regards the oscillating press, this arrangement permits of fixing the base of the connecting beam at any point whatever of its travel, when it is desired to dismount the piston. Further, it permits of maintaining the shears in an invariable position in case of sudden damages to the piping.

In order to produce the three powers of 25, 75, and 120 tons required by the programme, and at the same time expend in each case a corresponding quantity of water under pressure, it is of course necessary to cause the pressure of the motive water to vary in the same proportion as the stress to be extended. This result is reached by calculating the diameter of the two cylinders in such a way as to obtain the mean power of 75 tons, in making the water of the general conduit act directly under the normal pressure of 50 atmospheres. For the powers of 25 and 120 tons, use is made of an automatic multiplier, that consists of two cylinders arranged end to end, in which move pistons, A and B (Fig. 3), of different diameters. When it is a question of lifting 120 tons, the water at 50 atmospheres actuates the piston, A, and the other forces into the lifting cylinder motive water under a much greater pressure. If the load to be lifted is but 25 tons, the water at 50 atmospheres actuates the piston, B, and A forces the water into the same cylinder at a much lower pressure. The same operations are effected in the other cylinder when the extreme loads of 25 and 120 tons are moved.

The shears are likewise provided with a hydraulic cylinder, E (Fig. 1), placed on the back of the beam, B, and serving, through a cable, to bring the piston of the large cylinder to the end of its upward stroke, and for certain accessory work.

Finally, the apparatus as a whole is completed by an accumulator containing in reserve a large part of the water necessary for each operation.

The apparatus is capable of lifting a maximum load of 120 tons from 22 feet beneath the wharf to 22 feet above, and of moving it from 28 feet beyond the edge to 16 feet back of it, say a total of 44 feet. The cylinders of the lifting and oscillating presses are 1-3/4 feet in diameter and 4 inches in thickness. The stroke of the second is 22-1/2 feet. The length of the uprights is 110-1/2 feet and that of the connecting beam is 109 feet. The apparatus has been tested under satisfactory conditions with a load of 140 tons.--_La Nature._

THE DISTRIBUTION OF HYDRAULIC POWER IN LONDON.

At a recent meeting of the Institution of Civil Engineers, a paper on the above subject was read by Mr. Edward Bayzand Ellington, M. Inst. C. E. The author observed that water power was no new force, but that, as formerly understood, it was limited in its application to systems of mechanism suitable for the low pressures found in nature. The effects obtained by the use of high pressure were so different in degree from all previous experience, that a new name was needed, and had been found in the term "hydraulic power." Bramah's genius produced the hydraulic press, and he clearly foresaw the future development and great capabilities of his system; but it was reserved for Lord Armstrong to work out and superintend the intricate details that had to be developed before the system could be made fully serviceable. The public supply of hydraulic power in London constituted the latest development of this system. The hydraulic power was supplied through mains charged by pumping at a pressure of 700 lb. per square inch. The first and largest pumping station had been erected on a site known as Falcon Wharf, about 200 yards east of Blackfriars Bridge. The engine house at present contained four sets of pumping engines, each set being capable of exerting 200 I. H. P.

The engines were vertical compound, of a type comprising the advantages of a three-throw pump with direct connection between the pump plungers and the steam pistons. Each set of engines would deliver 240 gallons of water per minute into the accumulators at 750 lb. pressure per square in. at a piston speed of 200 ft. per minute. This was the normal speed of working; but, when required, they could be worked at 250 ft. per minute, the maximum delivery being 300 gallons per minute. The condensing water was obtained from storage tanks over the engine house, and was returned by circulating pumps to one or other of those tanks. The water delivered into the mains was maintained all the year round at temperatures of between 60 deg. and 85 deg. The boilers were of the double flued Lancashire type, and were made of steel. All were fitted with Vicars' mechanical stokers. At the back of the boilers was a Green's economizer, consisting of ninety-six tubes. The economizer and the stoker gear and worm were driven by a Brotherhood three cylinder hydraulic engine. The reservoir of power consisted of accumulators. The accumulators at the pumping station were two in number, each having a ram 20 in. in diameter and 23 ft. stroke.

The weight cases were of wrought iron, and were filled with iron slag. The total weight of the case and load on each ram was approximately 106 tons, corresponding to a pressure of 750 lb. per square in. The storage tanks formed the roofs for the engine and boiler houses. The water for the power supply was obtained from the river Thames, and was pumped into the tank over the engines. The water passed through the filtering apparatus by gravity into the filtered water tank over the boiler house, which was 7 ft. below the level of the unfiltered water tank. The filters consisted of cast iron cylinders, and each contained a movable perforated piston and a perforated diaphragm, between which was introduced a quantity of broken sponge; the sponge was compressed by means of hydraulic pressure from the mains. The delivery of power water from the Falcon Wharf pumping station was through four 6 in. mains. The most distant point of the mains from the accumulators was at the west end of Victoria Street, and was 5,320 yards, or just over three miles. To provide for all frictional loss in the pipes and valves, the accumulators had been loaded to 750 lb., the stated pressure supplied being 700 lb. per square in. The total length of the mains at present laid was nearly twenty-seven miles. The mains were laid in circuit, and there were stop valves at about every 400 yards, so that any such section of main could be isolated.

The method employed for detecting leakage was based upon an automatic record of the number of gallons delivered into the mains, and in cases of abnormal increase during the night, if found to arise during the early hours of the morning, the mains were tested. The power water used was invariably registered through meters on the exhaust pipes from the machines, and from the meters passed to the drains. There was a sliding scale of charges from 8s. to 2s. per 1,000 gallons at 700 lb. pressure per square inch, designed to meet, as nearly as possible, the variable conditions and requirements of consumers. The more continuous the use, the lower the charges. The scale was intended chiefly for intermittently acting machinery, and experience had fully proved that these rates were sufficiently low to effect a large saving to the consumer in almost all cases, whether for a large or a small plant. The author believed any idea of supplying power from a central source at rates much below these to be chimerical. The practical efficiency of the hydraulic system might be fixed at from 50 to 60 per cent. of the power developed at the central station. No other method of transmission would, he thought, show a better result; and the general convenience and simplicity of the hydraulic system were such that its use would hardly be affected, even if there were no direct economy in the cost of working.

In addition to the general supply of hydraulic power, in the City and adjoining districts, to the six hundred and fifty machines at present worked, a new departure had been taken by the application of hydraulic power to an estate at Kensington Court--the name given to an area of about seven acres opposite Kensington Gardens. Seventy houses and dwellings were to be built on this estate, of which thirty had been already erected. Each house was fitted with a hydraulic lift, taking the place of a back staircase, and the power supply was provided on the estate expressly for working these lifts. The driven machinery was of as great importance to an economical and satisfactory result as the distributing plant, but this obvious fact was not always understood. General regulations had been prepared by the author, defining the conditions to be observed by manufacturers in fitting up machinery for connection to the power mains.

They were intended to secure safety, and an efficient registration of the quantity of power used; but they left the question of the economy and of the efficiency of the machines to be settled between the consumers and the makers. In London more lifts were working from the mains and more power was used by them than by any other description of machinery. The number of all classes at present at work was over four hundred. The principal types in use were fully described. In some cases there had been, by adopting the public supply, a saving in the cost of working of about 30 per cent., as compared with the steam pumping plant previously in use.

Lifts were now becoming so general, and the number of persons who used them was so great, that the author considered it necessary to urge the importance of securing the greatest possible safety in their construction, by the general adoption of the simple ram. Suspended lifts depended on the sound condition of the ropes or chains from which the cages hung. As they became worn and unreliable after a short period, it was usual to add safety appliances to stop the fall of the cage in case of breakage of the suspending ropes; but they could not be expected to act under all circumstances. As an indication of the important part which lifts occupied in a modern hotel, it might be mentioned that at the Hotel Metropole there were, including the two passenger lifts and that for the passengers' luggage, no less than seventeen hydraulic lifts in use day and night, while the work done represented about 2,000 tons lifted 40 ft. in this time. The next largest use of the power was for working hydraulic cranes and hoists of various kinds along the river side, and in the city warehouses. It often happened that the pressure in the power mains was not sufficient for pressing purposes.

The apparatus known as an intensifier was then used, by which any pressure required could be obtained. Hydraulic power was also used at Westminster Chambers, and elsewhere, for the purpose of pumping water from the chalk for domestic use. The pump was set going in the evening and continued working till the tanks were full, or until it was stopped in the morning. For work of this kind, done exclusively at night, a discount was allowed from the usual rates. Mr. Greathead's injector hydrant, made at the Elswick works, had been in use to a limited extent in London in connection with the power mains.

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

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

{ Post attachment:
{ Bearing area, 6,600 x 3-1/3 = 22,000 lb. per square inch.
{ Single shear, 5,000 x 3-1/3 = 16,600 psi.
Rivets. { Web and flange connections, end rivets:
{ Bearing area, 20,000 x 3-1/3 = 66,600 psi.
{ Double shear, 5,800 x 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 8-1/2 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.

, in the cortical parenchyma indicates where the new cork cambium will be developed: when this is formed, all the tissues (e.g. _pa_, C_l_) lying on the outside of the new cork will die, and constitute (together with the cork) the true _bark_.]

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 malveceae, 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.

The above brief account may suffice to give a general idea of what the cortical jacket covering our timber is, and how it comes about that in the normal case the thickening of the cylinder is rendered possible without exposing the cambium and other delicate tissues: it may also serve to show why bark is so various in composition and other characters. But it is also clear that this jacket of coherent bark, bound together by the elastic sheets of cork, must exert considerable pressure as it reacts on the softer, living, succulent parts of the cortex, trapped as they are between the rigid wood cylinder and the bark; and it is easy to convince ourselves that such is the case. By simply cutting a longitudinal slit through the cortex, down to near the cambium, but taking care not to injure the latter, the following results may be obtained. First, the bark gapes, the raw edges of the wound separating and exposing the tissues below; next in course of time the raw edges are seen to be healed over with cork--produced by the conversion of the outer cells into cork cells. As time passes, provided no external interference occurs, the now rounded and somewhat swollen cork-covered edges of the wound will be found closing up again; and sooner or later, depending chiefly on the extent of the wound and the vigor of the tree, the growing lips of the wound will come together and unite completely.

But examination will show that although such a slit wound is so easily healed over, it has had an effect on the wood. Supposing it has required three years to heal over, it will be found that the new annual rings of wood are a little thicker just below the slit; this is simply because the slit had released the pressure on the cambium. The converse has also been proved to be true--_i.e._, by increasing the pressure on the cambium by means of iron bands, the annual rings below the bands are thinner and denser than elsewhere.

But we have also seen that the cambium is not the only living tissue below the bark: the cortical parenchyma (_pa_) and the cells (_c_) of the inner cortex (technically the phloem) are all living and capable of growth and division, as was described above. The release from pressure affects them also; in fact, the "callus," or cushion of tissue which starts from the lips of the wound and closes it over, simply consists of the rapidly growing and dividing cells of this cortex, _i.e._, the release from pressure enables them to more than catch up the enlarging layer of cortex around the wound.

An elegant and simple instance of this accelerated growth of the cortex and cambium when released from the pressure of other tissues is exhibited in the healing over of the cut ends of a branch, a subject to be dealt with later on; and the whole practice of propagation by slips or cuttings, the renewal of the "bark" of cinchonas, and other economic processes, depend on these matters.

In anticipation of some points to be explained only if these phenomena are understood, I may simply remark here that, obviously, if some parasite attacks the growing lips of the "callus" as it is trying to cover up the wound, or if the cambium is injured below, the pathological disturbances thus introduced will modify the result: the importance of this will appear when we come to examine certain disturbances which depend upon the attacks of fungi which settle on these wounds before they are properly healed over. In concluding this brief sketch of a large subject, it may be noted that, generally speaking, what has been stated of branches, etc., is also true of roots; and it is easy to see how the nibbling or gnawing of small animals, the pecking of birds, abrasions, and numerous other things, are so many causes of such wounds in the forest.

(_To be continued._)

SIBLEY COLLEGE LECTURES.--1887-88.

BY THE CORNELL UNIVERSITY NON-RESIDENT LECTURERS IN MECHANICAL
ENGINEERING.

III.--THE EVOLUTION OF THE MODERN MILL.[3]

By C. J. H. WOODBURY, Boston, Mass.

BELT TOWERS.

The distribution of power has not always received the judicious treatment which its importance deserves. There are but few references to this question in the books on the subject, and these treat of methods that are not in accordance with the application of the art in its present state.

[3] Continued from SUPPLEMENT, No. 647, page 10331.

The lecture was illustrated by about fifty views on the screen, which cannot be reproduced here, showing photographs of mills and mechanical drawings of the methods of construction alluded to in the lecture.

The early form of the distribution of power consisted in placing a vertical shaft extending through the whole mill and distributing the power at each story by means of beveled gears, generally of skew-beveled form. The mechanical defects of such a method of distributing power, with regard to protection, repairs, and necessary care, are readily apparent, and there have also been many severe accidents caused by the breaking of teeth in these gears.

The present method of distributing power in this country is entirely by lines of belts extending up through what is known as a belt tower, which constitutes an element of great fire hazard to a mill. In some cases the belts are carried from story to story, covered by a casing of wood, and in other instances the tower forms a flue which may be the means of the rapid spread of fire throughout the building.

Before the introduction of automatic sprinklers there was not, I believe, a single instance of a fire entering the lower portion of a belt tower during working hours without accomplishing the destruction of the mill. Since the equipment of such places with automatic sprinklers, there have been several fires of this nature extinguished with nearly nominal damage. That is to say, the hazard of fire starting in such places is beyond the capacity of any apparatus other than automatic sprinklers to cope with it.

It would be impossible to arrange the distribution of power in many mills to conform to conditions of safety without reorganizing the whole plant, which would, of course, be impracticable. But in many instances modifications can be introduced which will diminish the hazard to a great degree. When the pulleys and belting are covered with sheathing in each room, the continuity of these flues can be broken by removing this sheathing down to the height of four or five feet above the floor, so that the covering will merely constitute a physical protection to any one approaching the belting.

The best method of arranging the belt tower has been in the case of a mill at Fall River, which was erected upon the ruins of a building destroyed by a fire originating in the belt tower. The machinery is driven by a steam engine situated in an ell projecting from one side at about the middle of the mill; and the main belt communicates to pulleys in a stone masonry tower located directly inside the walls of the main mill; and thence, from pulley to pulley, the power is communicated to each floor by shafting passing through holes left in the tower, and in no instances by means of belts.

There is a separate stairway inside of the tower for lubricating the journals, etc., and the top of the tower is covered with skylights protected underneath by a wire netting. In case of a fire in the belt tower, the heat will readily break the glass at the top, and the fire will tend to go up and out of the tower rather than through the mill.

MILL FLOORS.

The questions involved in designing the floors of a mill are of great importance, contributing in no small measure to elements concerned in the successful operation of the mill, and to a greater extent to its standing as a fire risk, and therefore affecting the constant expense of insurance.

In the case of a building designed merely for sustaining of loads, as in a storehouse, a floor would naturally be designed on the basis of considering the breaking strength of the timber. But in the case of a mill, the limitation is the amount of flexure allowable under the circumstances; and therefore the floors of the building are made more nearly rigid than would be required merely from the consideration of the ultimate strength of the structure.

The books on the subject, repeating over a constant which was first, I believe, given by Brunel in testimony before a parliamentary commission, have held that one four-hundredth of a span is the proper ratio of flexure. This may have been a very good rule to give to the parliamentary commission, but it is hardly the practical method of limitation for a matter of engineering construction, because the flexure of a loaded beam is in the form of a curve, and therefore its law is that of a curvilinear function, and not of a straight line. I have examined a great number of precedents of good construction in this connection, and for mill use have deduced the formula for deflection in inches, _d_ = 0.0012 L squared, in which L is the length of span in feet. It will be readily recognized that the true constant of deflection of span is measured by the radius of curvature which will give a uniform and allowable distortion to the floor in either direction to the limit of the radius upon which this formula is based, which is 1,250 feet.

I do not propose to offer to you on this occasion any remarks in regard to the treatment of the mathematics of the problem of applied mechanics concerned in the questions of transverse stress, knowing that you have certainly received instruction upon these subjects. But referring to the questions of mill floors, I would state that Southern pine beams of solid timber twelve by fourteen up to fourteen by sixteen inches are used; and instead of attempting the use of one piece of timber, it is preferable to use two pieces of the same depth and of half the breadth. These should be bolted together, with a space of an inch or so between them left by placing small vertical pieces of wood between the timbers when they are bolted together. In this manner one is more sure of sound timber, and in the process of seasoning there is less liability of dry rot in the interior, or of injurious checking, warping, or twisting.

The end of the beams should rest upon iron plates in the masonry, and should be secured by means of a tongue upon the plate entering a groove across the lower side of the beam. It is not feasible to make this groove to a close fit with the tongue; but it is cut a great deal larger, and the whole brought to a firm bearing by means of pairs of wedges or quoins driven into the groove each side of the iron tongue.

The outer end of the plate contains ribs or tongues reaching down into the brickwork. In this manner the timber is securely fastened to the brickwork; and yet in time of accident or of fire the falling of the beam in the middle of the mill will raise it up sufficiently so that it will clear the tongue and fall without tearing the wall down, which is the case whenever the beams are secured by bolts entering the end of the beam from the face of the wall.

At the points of support in a line of columns, the beams should be free from all compressive stress, transmitted through the lines of columns from floors above, by means of iron pintles between the cap of one column and the floor of the next one carrying this load.

A faulty method of construction, quite frequently used, consists in covering each column with a bolster of timber, four or five feet long, reaching out under the floor beams.

The transverse contraction of wood in seasoning after it is in position in the mill varies from three-eighths of an inch to double that quantity per foot; and the aggregation of such shrinkage amounts to a very considerable distortion or settling of the floor in a mill of several stories. Moreover, the resistance of timber to transverse crushing has been shown by experiments on the testing machine at the United States arsenal at Watertown to be about three times the resistance to longitudinal crushing.

Iron columns for mills have been entirely displaced by those of timber, as it was found that the latter were more reliable in resistance to fire, were freer from defects in construction, and possessed less tendency to vibration. A series of tests on full-sized mill columns of various forms of construction and age, made in the experiments referred to, at the Watertown arsenal, showed that resistance to crushing of Southern pine columns was about 4,500 pounds to the square inch, and remarkably uniform as to the different results. In white oak there was a wider range, owing to the difference in the grain of the various samples, the generality of the specimens being of somewhat less resistance than that of Southern pine.