1841.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



167 



" Description of a Thirty-Ton Crane, erected on the Quay of Earl Grey's 

 Dock, Dundee Harbour." By James Leslie, M. last. C.E. 



The Crane is placed on a stone platform sixteen feet square, raised six feet 

 above the level of the Quay, with its centre seven feet back from the Dock 

 face i and as the sweep or radius is thirty-five feet to the perpendicular of the 

 jib-sheave, the load is suspended twenty-eight or twenty-nine feet over the 

 Dock (as the double or single purchase sheave is used). The height of the 

 sheave above the level of the Qnay is forty feet. 



Instead of the framing revolving about a fixed post, as in the usual mode 

 of construction, the post itself is connected with the framing, and turns with 

 it, so that the strain may be always in the direction of the greatest strength. 



To avoid the extra dimensions of the castings for the post, if it bad been 

 composed entirely of cast iron, and for facility in the construction, the parts 

 of cast and wrought iron are so combined that the "push" is thrown upon 

 the cast-iron abutting piece which is placed in front, wliile the back part, 

 consisting of wrought-U-on tension bars, bears the " pull." Tlie two ring.s on 

 the post are turned on the face and edges, and being bolted together form a 

 fair surface for the friction rollers, while the back forms a rest for the tension 

 bars. 



These back tension bai'S are three inches wide by two and a half inches 

 thick, each, forming an aggregate section of forty-five inches. They were all 

 proved in the bent form in which they are used, by making fast the ends of 

 each bar to cross heads held apart by two logs, and suspending a load of 

 twenty-four tons from the elbow formed by the bend in the bar ; this was 

 calculated to be equivalent to a longitudinal strain of ninety tons. There are 

 also two side tension bars, two inches square each, firmly sunk in the cast- 

 iron block, and bolted to the top of the framing. 



The post revolves within a cast-iron cylinder twenty-seven feet deep, five 

 feet three inches diameter, with turned and bored water-tight joints. The 

 whole is surrounded with masonry, bound together by strong iron hoops and 

 diagonal tie bars passing through the fixed ring. 



The jib is of oak two feet diameter in the middle, and twenty-one inches 

 at the ends ; the two wronght-iron jib stays are each three and a half inches 

 diameter; the chain is of 1 J inch iron. Eight men easily lift a weight of 

 thirty tons, and by means of the horizontal wheel-work one man can turn it 

 round. 



The total weight of the castings, wrought-iron bars, chain, and brasses, is 

 about fifty-nine tons. 



The crane was made and erected by Mr. Borrie, of Dundee, from the de- 

 signs and under the direction of the author. 



The communication is accompanied by two elaborate working drawings, 

 on a large scale, with details of the mode of construction. 



" A Refrigerator, or Machine for cooling Breioer's Wort." By Robert 

 Davison, M. Inst. C.E. 



The macliine described in this paper was constructed for the purpose of 

 ascertaining the most expeditious process for cooling wort, without deteriorat- 

 ing the quality of the liquor. 



Two kinds of preliminary experiments were made, viz. — 



1st. As to the rate of cooling Ijy simple exposme to the atmosphere in the 

 ordinan- shallow vessel, having a superficial area of 420 square inches, the 

 liquor being 1 J inch deep. 



2nd. As to the rate of cooling, under similar circumstances, with the as- 

 sistance of air mechanically driven over the surface of the liquor at difierent 

 velocities. 



In both cases the loss by evaporation was noted. 



The numerous experiments are detailed in a tabular form, whence may be 

 selected three series, which will give the average relative results. 



A higher velocity than 84^ miles per hour was found prejudicial, as a por- 

 tion of the wort was driven over the side of the vessel. 

 The relative loss by evaporation was 



By natural cooling 1'40 



By blast, at 32 miles per hour 1-45 



Ditto at 57 miles 1'4" 



Hence it would appear, that the evaporation effected was about the same 

 in all the experiments ; and the rate of refrigeration nearly in the direct ratio 

 of the velocity of blast. 



These results induced the author to try other applications of the blast, by 



causing the wort to flow down over a series of slightly inclined planes, being 

 exposed at the same time to a powerful ascending current of air from a fan 

 blower. The introduction of air directly into the wort was, however, found 

 to raise a froth or " fob," which would aft"ect the soundness of the beer. 

 Several other methods were tried, and at length the machine now described 

 was constructed. 



Tlie wort is pumped u]) at a slow and regulated speed into a recipient at 

 the top of the machine, divides into a series of thin films or streams, and 

 trickles down the inside of a number of thin metallic tubes, set vertically, 

 with their upper extremities quite level. Up these tubes is forced a current 

 of air at any required velocity, which, meeting the descending wort, cools it 

 inside, whilst a constant change of cold water takes place around the exterior 

 of the tulies. The wort, on leaving the vertical tubes, is received into a 

 second refrigerator, containing a number of horizontal pipes through which 

 cold water flows. By this process the wort is cooled without producing any 

 prejudicial efiect upon its quality, and with a rapidity (as shown by tlie table) 

 wliicb would be extremely advantageous under certain circumstances. 



Tliis communication was accompanied by two drawings of the Refrigerator, 

 and illustrated by a working model with which the experiments had been 

 made. 



" An Account of the Repairs and Alterations made in the Structure of the 

 Menai Bridge, in consequence of the damage it received during the gale of 

 January 7, 1839." By T. J. Maude, Grad. Inst. C.E. 



The roadway of the iVIenai Bridge having beeu seriously injured by the 

 storm of January 7, 1839, it was deemed expedient to renew entirely the 

 suspended platform : and at the same time to carr\- into effect certain altera- 

 tions in the construction, suggested by constant observation of the working 

 of the Bridge during thirteen years, as well as its condition after the storm. 



■ In the original structure, each long roadway bar was fixed at three points 

 to the vertical suspending rods. Motion being chiefly communicated to the 

 roadway by the vibration of the windward chain, one end of the long bar sus- 

 pended from it was lifted up, whilst the other two points of suspension re- 

 mained nearly stationary. The bar thus became a lever with its fulcrum at 

 the middle point of attachment, and at that weakest part it invarialily broke. 

 In order to remedy this defect, an augmented depth of half an inch has been 

 given to the new roadway bars, with an additional enlargement round the 

 eyes for attachment to the suspension rods, and each bar is hnng from two 

 points only, permitting it to play when the Bridge is subjected to motion. 



The same vibratory action occasioned frequent fracture of the suspending 

 rods close to the surface of the platform ; to s\ich an extent, that during the 

 storm a great portion of the platform was entirely torn from its fastenings 

 on one side, and hung down flapping in the gale supported merely by one 

 Une of rods. To remedy tliis, a joint has been introduced in each rod just 

 above the surface of the platform, so as to allow the suspension rods free ac- 

 tion, and ])ermit a motion in either of the carriage-ways or the footpath in- 

 dependently of each other. The dimensions of the short suspension rods 

 have been increased to one inch and a quarter square, whilst the remainder 

 of the rods are only one inch square. The effects of the lateral and undulat- 

 ing motions are provided against by the direction of the working of the joints, 

 one of them being in the line of the roadway bar, and the other at right 

 angles to it. 



Additional rigidity has been given to the platform by applying a course of 

 three-inch planking laid transversely throughout its entire length, and bolted 

 through each plank at intervals of two feet six inches apart, the oak beams 

 originally placed beneath the platform having been entirely removed. 



For the purpose of checking longitudinal undulation, two lines of beams, 

 formed of two pieces of Baltic fir, each 40 feet long, 13 inches deep, and 4J- 

 inches thick, are framed to the trussed bearers, and bolted up beneath each 

 carriage-way the entire length of the platform : at the same time an increased 

 depth has been given to the wheel guides, which are also bolted through to 

 to the planking. The total depth given by these strengthening beams and 

 guides, is three feet four inches, while in the original structure it was one 

 foot four inches. 



The weight of the additional timber and iron-work introduced into the 

 bridge, is about 130 tons. The whole of the timber has been Kyanized, and 

 each coat of planking covered with Archangel tar ; the felt has been discard- 

 ed, as it does not appear to have answered its intended objects in the original 

 structure. 



In these alterations (which were designed by Mr. Provis, M. Inst. C.E.) 

 one main object, which was never lost sight of, was to preserve that simpU- 

 city of construction which is so striking a feature in the original design; and 

 should any future derangements occur, any part can be repaired or replaced 

 without disturbing the rest of the stmctiure. 



This communication was illustrated by a drawing of the original platform, 

 and of the alterations described in the Paper. 



February 2. — The President in the Chair. 

 " On a Method of setting out involute Teeth of Wheels, so that any two 

 wheels of the same or of different diameters will wort truly together, whether 

 the teeth bottom or only just touch each other." By Edward Cowper. 



The rule is briefly this : — 



Point off the teeth on the pitch circle in the usual manner ; then take the 

 smallest wheel of the set, and having decided upon the depth of the proposed 

 tooth, describe a circle (caUed the Evolute) touching the bottom of the tooth. 



