20 



NATURE 



[May 7, 1891 



cynocephalus <J ? ), three Ursine Dasyures {Dasyurus 

 ursinus <J 9 9 ) from Tasmania, two Brush Turkeys ( Talegalla 

 lathatni <J ? ), four Australian Wild Ducks {Anas superciliosa) 

 from Australia, received in exchange ; a Black Lemur {Lemur 

 macaco), two Persian Gazelles {Gazella subgutturosa), born in 

 the Gardens. 



THE INSTITUTION OF MECHANICAL 

 ENGINEERS. 



ON the evenings of Thursday and Friday of last week, the 

 30th uit. and the ist inst., the Institution of Mechanical 

 Engineers held an ordinary general meeting ; the President, Mr. 

 Joseph Toinlinson, occupying the chair. There was an at- 

 tendance of members somewhat in excess of that which is 

 usual at the ordinary meetings of this Institution. There were 

 two items on the programme — namely, a paper on Lancashire 

 boilers, and a further report from the Research Committee on 

 Marine En/ine Trials. The discussion of the latter occupied so 

 much time that the boiler paper had to be shelved until next 

 meeting. 



The latest steamer upon which the Marine Engine Research 

 Committee has been experimenting is a cargo vessel named the 

 lona. She was built and engined by W. Gray and Co., of West 

 Hartlepool, and is a good modern example of what can be done 

 in fuel economy with triple expansion engines when high speed 

 is not aimed at. This latest report of the Committee should 

 re-establish in some minds the belief in the economy of the 

 marine surface-condensing engine, which had been, so it was 

 thought, rather shaken by the previous labours of the Committee. 

 When on the first trials of the Committee the fuel consumption 

 of the Meteor, Fusi Yama, and the Colchester came out at not 

 less than 2 pounds of coal per indicated horse-power per hour 

 — the Colchester' s consumption being nearly 3 pounds per 

 hour — it was said, by those who had never believed in the 

 claims of marine engineers, that the bubble was pricked by a 

 trial made by competent and unbiassed persons. It is true the 

 Tartar's trial improved on these figures, the coal consumption 

 comingout 177 pound per indicated horse-power per hour ; still this 

 is some way behind the \\ pound of which marine engineers 

 had been boasting. The experiments with the lona, now under 

 consideration, have rehabilitated the marine engine as an 

 economical form of steam motor, for there can be no doubt that 

 the engines of that vessel have given off on trial one unit of 

 power per hour for less than the pound and a half of coal, and 

 we have no reason to think that the i '38 pound shown on the 

 chief engineer's independent trial is not a fair average for sea 

 running when the disturbing element of measuring tanks is omitted. 

 The lona is a well decked vessel, built in 1889. She has 

 ■triple expansion engines on three cranks, working a single screw. 

 The vessel is 275 'i feet long, 37*3 feet wide, and 19 feet deep 

 in the hold. Her moulded depth is 21 feet 10 inches, and her 

 coefficient of fineness is 0765. She has a cellular bottom. Her 

 mean draught in dock before trial was 20 feet 8 inches, but she 

 rose half an inch in salt water, the displacement being 4430 

 tons. The engines had been freshly overhauled. The trial 

 took place off the east coast, between Robin Hood Bay and 

 Great Yarmouth. The weather was fine throughout. The engines 

 are triple compound surface condensing. The cylinders are placed 

 in the order — intermediate, high, low, going from forward to aft. 

 The cranks rotate in the sequence— hi^h, intermediate, low. 

 The diameters of the cylinders are 21 "88 inches, 34 02 inches, 

 and 56*95 inches ; the stroke is 39 inches. The high pressure 

 cylinder only is jacketted, steam being taken from the boiler 

 direct. Outside this jacket are the receivers for the inter- 

 mediate and low pressure cylinders. The jacket steam therefore 

 parts with heat to the high pressure cylinder, and also heats up 

 the steam passing to the two other cylinders. The arrangement 

 is unusual but not new, A feature worth noting in the present 

 ■day is that the steam distributing valves are all slide valves. 

 Mr, Mudd, the designer of the engines, does not follow the 

 modern fashion of using piston valves, it being his belief that 

 the advantages they offer are not equal to those lost. The 

 surface condenser has 1360 square feet of tube surface. There 

 ■are two ordinary steel boilers having 42 square feet of grate 

 -surface, the total heating surface being 3160 square feet ; which 

 is equal to 75*2 times the grate area. It is not to be wondered 

 at that, with this liberal allowance of heating surface, the fuel 

 ■economy came out very satisfactorily. The total cross-sectional 



NO- 1 1 23, VOL. 44] 



area through the tubes is 18 "3 square feet, and the area across 

 the funnel 307 square feet. A notable feature about this vessel 

 is that the boilers are worked on forced draught ; or rather there is 

 a fan for supplying air to the fires, for a pressure equal to only 0T7 

 inch of water in the ash pits hardly fulfils the popular notion of 

 forced draught. The steam for driving the fan engine was supplied 

 from the donkey boiler, and therefore the measurements of 

 quantities in the performance table were not affected by the 

 amount of steam used by the fan. The matter is not one of 

 great importance — the power to drive the fan not being, per- 

 haps, more than the three-hundredth part of the power of 

 the propelling engines ; but we question whether it is strictly 

 fair — as comparing the Zona's machinery with that of 

 other vessels — not to take the fan-engine steam from the 

 main supply. The boilers in this ship have an extra- 

 ordinarily large proportion of tube surface as compared to the 

 grate surface, and this would be likely to lead to an insufficiency 

 of draught were the lighter specific gravity of the chimney gases 

 alone depended upon. If, therefore, the aid of the fan has to 

 be brought in, its cost as well as its services should be taken 

 into account. This is looking at the matter from the point of 

 view of taking the total efficiency of the machinery, and Prof, 

 Kennedy might very justly urge that the steam used by the fan 

 would be a disturbing element, and prevent him from properly 

 determining the efficiency of the engines. The fan undoubtedly 

 belongs to the boiler, but not more so than the feed-pumps ; 

 all boilers, however, must have feed-pumps, while comparatively 

 few have fan-engines. If ever it comes to be that fan-engines are 

 almost as much matters of course as feed-pumps, it will be con- 

 venient to class the former with the engine, but until then it is 

 as well to estimate the steam required for forced draught pur- 

 poses by itself; still it should be taken into account. 



The air from the fans is taken to the furnace through gridiron 

 valves, wh ch close automatically when the furnace-door is 

 opened, so as to prevent a rush of flame into the stokehold, A 

 small jet of air is also admitted through the wet end of the 

 boiler back by a passage made for the purpose. In this way 

 there are two streams of air which meet in the combustion- 

 chamber. There is also a hanging bridge attached to the back 

 tube plate, and depending into the flame box at the back of the 

 bridge. By these arrangements a very thorough mixing of the 

 air and furnace gases is secured ; and to this, no doubt, is due 

 the unusually perfect combustion which was obtained on the 

 trial. The small grates give additional space for the mixing and 

 burning of the gases before they enter the tubes, a most desir- 

 able feature in boiler design, and one which should do much to 

 put the cylindrical flues of modern high-pressure boilers on an 

 equality, in the matter of combustion, with the rectangular 

 furnaces of the comfortable low-pressure days of the past genera- 

 tion of marine engineers. At the same time we must not forget 

 that a large amount of fuel burnt on a small grate requires a 

 large combustion chamber. It is the volume of gases evolved 

 which has to be considered. It should be stated that the arrange- 

 ment for forced draught was designed by Mr. J, R, Fothergill, of 

 Hartlepool, engineer superintendent to the firm owning the ship. 

 It is so difficult to get accurate data upon the weight of marine 

 engines, that we add the figures given in the report : — 



Tons. 



Engines alone 94 "92 



Shafting, tunnel-bearings, and propeller ... 26 "59 



Engine room auxiliaries, including donkeys, 

 _ pipes, platforms, ladders, and gratings ... I2*i6 



Boilers alone S^'^o 



Boiler-room auxiliaries, including forced draught 

 gear, smoke-box, uptake, funnel, furnace gear, 

 mountings, stokehold floor, boiler-chocks, 



and ties 28*49 



Water in boilers .. 3575 



Total 



228*22 



The coal used was of good quality. The following analysis 

 (as used) will be of interest :— 



Per cent. 



Carbon 82*34 



Hydrogen 5'47 



Moisture I "94 



Ash 2-90 



Nitrogen, sulphur, oxygen, &c., by difference... 7*35 



