300 



THI<: CIVIL I5NGINEKR AND ARCHITECTS JOURNAL. 



[October, 



with the weights a, b, c, . .at the respective ilislance log A, log B, log 

 C, . .fioni the point of suspension. 



Involution, evolution, compound rule of three, and many other c;d- 

 culations of that kind, are but very particular cases of the preceding 

 fonnula. 



REVIE^VS. 



An Esaay uii the Bvikrs of Skam Engines. By R. Armstrong, Civil 



Engineer. London, Jolm Weale, 1839. 



A new edition of this excellent work has appeared with additions, 

 making it more complete, and consequently more deserving tlie atten- 

 tion of the public, tlie various rules and practical data which abound 

 in it, entitle it to be considered a text-book for boiler makers, as well 

 as boiler users. Having largely quoted from its contents in our former 

 notices, nothing of a very material character presents itself, which we 

 can transfer into our pages, but perhaps the following may be inte- 

 resting to some of our readers : — 



General Rules for proporiionhig Hip leiu/th of Boilers. 



Rule I. A plain boiler mthout any inside flno, to he hung upon what is 

 called the " oven plan,"* ought not to exceed in length six times the square 

 root of the horse power in feet, or in ordinaiy circumstances, six times tlie 

 square root of the area of the fire-grate in feet. 



Rule II. A boiler without any inside flue, to he set up in the common 

 way with a wheel draught, ought not to exceed in leagth four times the 

 square root of the horse power ; or four times the square root of the area 

 of the fire-grate in feet. 



Rule III. If a fined boiler, or boiler containing one or Inore inside flues, 

 (and the latter pass quite through,) is to be set up with a sjilit draught, it 

 ought not to exceed in length three and a half times the square root of the 

 horse power, and if ^^'ith a wheel draught, three and a quarter times the 

 same, or three and a quarter times the square root of the area of the fire- 

 grate in feet. 



Riile IV. If a fined boiler with an inside uptake, like a Boulton and Watt 

 boiler, (Art. 82,) is to be set up with a split draught, it need not exceed iu 

 length from three to three and a quarter times the square root of the horse 

 power ; or if it is to he set up with a wheel draught, then the length of the 

 boiler ought not to exceed three times the square root of the horse power, 

 or of tlie area of the fire-grate in feet. 



The author, after detailing some experiments on the rate of com- 

 bustion and evaporation, proceeds to describe the boiler by which 

 those experiments were made : — 



This boiler was pm-posely chosen of this simjile and eleineutary form, and 

 set up ill the cheapest and simplest manner ; that is, upon the " oven ])lan," 

 so that all alterations or improvements that it might have been found expe- 

 ij)ent to make, either in the setting or the construction of the boiler itself, 

 might he in the shape of additions merely, and therefore capalile of being 

 separately proved, both as to first cost and profit ; and also that obsenations 

 might be made upon it, for a sufficient length of time, ^^ itbout the liabUity 

 to error arising from complication of construction, or iiiternqition from the 

 necessi'y of cleaning out flues or othenvise. It was thus made to answer 

 the purpose of a trial boiler in order to guide the firm to which it belonged 



K«- 1- 



ill their choice of what kind of boiler to adopt in the erection of new 

 works then contemplated by them. 



The following figure re]ircscnts a longitudinal section through the centre 

 of the boiler, furnace and cbiiuney, in all respects proportional exrept as to 

 length, wliicli is to a scale of on"-lialf of that for the depth and width, and 

 fig. 2 represents a plan, or bird's-eye view, of tlie furnace, flame lied, 

 chimney, &c., supposing the boiler to be removed : and the same letters 

 refer to the same parts in both figures. The boiler is bung upon east-iron 

 brackets, rivetted to its sides a little above the centre, and with broad 

 flanges resting upon the top of the side walls, as is shown in the cross sec- 

 tions, figures ?> and 4. It is fixed in an inclined position, or with a fall 

 of about S inches to the front, so that by far the greatest proportion of the 

 water is brought immediately over the furnace, as is shewn in fig. 1. A is 

 the fire-grate with the ordinary furnace bridge at the end of it, only that 

 the latter is provided with a longitudinal aperture, about 2 inches wide, 

 communioating by a channel at its bottom, with the external air at E, and 

 ]irovided with a valve, so that the smoke could be consumed upon Parkes's 

 princijile, if necessary. lint in ad'Ution to this, there is also another bridge 

 1!, at about half the length of the boiler, which divides the flame bed into 

 two chambers C C. The damper jilate D, is hung by side rods in tlie short 

 passage leading to the chimney, which is the only part that can be pro- 

 perly called a flue. The damper is inverted, or made to open downwards, 

 so that the current of smoke or hot air is made to pass over instead of under 

 it. The octagonal chimney is 30 yards high and 3 feet wide inside at the 



Kig. 2. 



top, and intended to be large enough for two such boilers, which it evi- 

 dently is. The following cut (fig. 3) is a cross section of the boiler taken 



* That is, without any return flue, but with the flame and smoke to pass 

 from the fire place directly under the bottom of the boiler to the vent or 

 chinmey. When the draught is arranged in this wanner, it is by some called 

 " a thorough draught." 



through the furnace at A, just iu front of the fire bridge. This bridge is 

 an inverted arch of the same radius as the boiler, and placed 8 or 9 inches 

 below the bottom of the latter. The second or flame bridge B, is princi- 

 pally for the purjiose of spreading the flame and heated air around the con- 

 vex Iieating surface of the boiler in a stratum of comparatively equal thick- 

 ness, and is considered an absolutely essential requisite when a lioUer is set 

 up upon the oven plan, and two or three such bridges are still more econo- 

 mical. They are usually called check bridges, from theu- tendency to check 

 or impede the rapid current of hot air in its passage to the chimney, and 

 consequently retain the heated gases longer luider the boiler, which they 

 certainly do', quite as cftectually as causing tlie smoke to pass through long 

 winding flues ; but this is perhaps the least important piu-pose they sul)- 

 serve. 



The flame bridge is shown in elevation in fig. 4, which is a cross section 

 of the boiler and flame bed at the middle of the length of the boiler. 

 This bridge is an inverted arch about five inches from the boiler, aud equally 

 distant all round. We may state here, that proper attention to the con- 

 struction of these bridges is a matter of considerable importance; some- 

 times people have done away v,iX\\ them altogether, aud theu an enormous 



