1849.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL, 



221 



BEVIE'WS. 



The Marble Steam-Engine, designed chief y for the ttse of Naval 

 Officers and Engineers. London: Hebert, 18-t9. 



The authors of this work are JMi'. Main, Professor at the Royal 

 Navy College, and Mr. Brown, Chief Engineer R.N. Their com- 

 bined talents Iiave produced a work of great interest to those en- 

 gineers who may be engaged in our steam marine; it contains 

 some valuable suggestions and hints that could only be given by 

 those who have liad extensive e.vperience in the engine-room. The 

 volume is well illustrated by numerous engravings, given in a re- 

 markably clear manner, which cannot fail conveying to the mind 

 correct notions of the whole of the details of the steam-engine. 

 A few exti-acts from the w ork will better show its true value than 

 any observations we may make in its favour. 



The First Chapter is introductory, and explains tlie nature of 

 Steam. The Second is an explanation of the Marine Engine, en- 

 tering into a minute description of each part, from the cylinder to 

 the grease-cups. The Third Chapter exjilains the different direct 

 action engines that were inti'oduced into the navy about four or 

 five years since; the Fourth Chapter is on Boilers; and the Fifth 

 on "Getting up the Steam." 



Instances in vhich it has been found (hat the Steam begins to escape before 

 the Pressure reaches the limit prescribed by the Safety- Valve, 



This happens mostly with large boilers, having in consequence propor- 

 tionally large safety-valves; and the explanatiun may be given thus. The 

 valve being of considerable size, and the spindle in the centre, the edge of 

 the valve is sprung off its seating, and allows the steam to pass. It becomes 

 a question for consideration, whether it would not be advantageous, now 

 that boilers are so large, to employ two valves instead of one. 



On the Causes of Priming when first Starting the Engines. 



One cause of priming at first starting the engines arises from the pressure 

 being taken off the surface of the water in the boiler, and thus enabling the 

 ebullition to go on with greater violence ; but this is nut the principal cause : 

 the chief reason is, that many foreign substances become niechaiiically mixed 

 with the water; for instance, on getting up the steam in a muddy river, such 

 as the Thames, the mud will, by boiling, be driven up to the surface of the 

 water, and accumulating there will prevent the free course of steam to the 

 steam chest, and consequently it forces up the water and mud before it. If 

 there be any mucilage in the water, priming will also take place. Such 

 water is formed in deep bays and harbours, especially at particular times of 

 tide, from the mixture of seaweed and deconiposing vegetable u. alter. 

 There are few persons who have not noticed this fact one way or another. 

 The cook well knows the tendency a vessel, containing other substances be- 

 sides water, has to boil over at tirst; and in making coffee the case is re- 

 markably exemplified : the whole mass will he observed to rise to the sur- 

 face of the coffee-pot when beginning to boil ; but after some time these 

 effects are not so remarkable. Two instances of priming from this cause 

 may be mentioned. As H.M.S.V. Avenger, Captain Dacres, was going into 

 the very deep bay at Killybegs, Ireland, as the vessel came to an anchor the 

 boilers primed to such an extent as to make it necessary to haul out the fires, 

 so much of tlie water left them through the waste steam-funnel and engines: 

 indeed, the engines were completely choked with it. Again, a short time 

 afterwards, in Arran Bay, the fires had been banked up all night, and to sup- 

 ply the loss by evaporation, water from the Bay had been pnujped at inter- 

 vals into the boiler; and consequently when the slides were moved to start 

 the engines (the water-surface in the boiler being suddenly relieved of its 

 pressure), the engines nearly stopped; and at each return of the stroke it 

 was feared the cylinder-covers and bottoms would have given way. Now 

 this never took place at sea, unless when the fires were urged. 



Some interesting facts may be stated connected with the new tubular 

 boiler fitted to the little 10 horse-power steamer Bee, attached to the Royal 

 Naval College to assist the students in gaining a practical knowledge of the 

 steam-engine. When steaming about the harliour, it is found that the boiler 

 begins to prime as the vessel approaches the inlets where there is the most 

 mucilage; and also if the water be blown out of the boiler, and afresh 

 snpply admitted, the priming afterwards will depend on the height and state 

 of the tide when the boiler is filled. If the boiler be refilled as the tide is 

 ebbing, especially at the time the water is leaving the mud, all hands are on 

 the look-out to find the engine-room flooded from the escape-valves ; hut it 

 it be filled as the tide is coming in from the sea, or when the water is high, 

 the same casualties are not expected. A boiler will likewise prime as the ves- 

 sel goes out of salt water into fresh, and also in going out of fresh water into 

 the salt : the first of these cases can be accounted for from the fact, that 

 fresh water boils at a lower temperature than salt water, and therefore as 

 the fresh water enters the boiler previously heated, the ebullition is more 

 violent; but the contrary case is difficult to explain; and indeed, this latter 

 instance would almost lead one to suppose the former explanation not to be 

 the true one. The same difficulty occurs in aticinpting remedies for prim- 

 ing; for melted tallow on the surface of some boilers will check the priming, 

 and in others it will increase it. 



We would not enter here into the real cause of priming — namely, the 

 form and dimensions of the boiler and steam-chest, because that is a matter 

 beyond the control of the engineer and officers of the ship ; but it is very 



clear that if a larger steam-space were allowed, and combustion took place 

 more slowly, and the boilers were nrtt so rontracted at the water-surface as 

 many of our marine boders are, we should not bear so much of priming. 

 It is probably true that those who have the management of the Cornish 

 engines scarcely know the meanine of the phrase. 



Chapters VI., ATI., and VIII. relate to "Duties to Machinery 

 when under steam, during action, and on arriving in harbour;" and 

 contain some valuable suggestions, from which we give the follow- 

 ing extract : — - 



On the Number of Boilers to be used when not going at full Speed, " 



There is a common practice in our steam navy, when employed on a service 

 in which particular despatch is not the object, to use half the number of 

 boilers, and proceed at a speed proportionably less, in order to consume less 

 fuel in traversing the distance. The saving thus effected depends on the 

 fact, that the consumption of fuel per hour varies as the cube of the speed, 

 and the consumption of fuel per mile depends on the square of the speed. 

 Suppose, for instance, a vessel to be furnished with four boilers, and that her 

 speed when using all four is 10 knots, her speed with two boilers would be 8 

 knots nearly. Let us suppose, for argument sake, each boiler consumed half a 

 ton an hour ; then, at full speed, 4 half tons, or 2 tons, would drive the ship 

 over 10 knots, or 1 ton would propel her over 5 knots. Again, in the 

 second case, 2 half tons, or 1 ton would send her over 8 knots. Hence we 

 should, by this method, gain 3 knots in distance for every ton of coal : and 

 we may set it down as a general maxim, that the slower a vessel goes, the 

 greater the distance she will steam over with the same consumption of fuel, 

 'this is on the supposition that she meets with no strong head-winds, &c., 

 such as to force her to use all her power. If, however, the wind or tide 

 would have the effect of making her go astern, her rate through the water, 

 for the greatest economy of fuel, should be at least half as great again as 

 she would have gone in the opposite direction if no power bad beeen used. 

 Thus, if a vessel be steaming up a river which flows at the rate of 4 knots, 

 her most economical speed would not be less than 6 knots, making good 2 

 knots over the grouijd. 



But it is a question for mature consideration, whether a still further saving 

 might tuit be effected by a different mode of managing the fires. Suppose, 

 for instance, as we at first had arranged, that the vessel he going at 8 knots, ' 

 using two boilers instead of four. The alteration we would propose is, that 

 instead of using two boilers she should use three ; but that the speed of the 

 ship should still not exceed 8 knots, which she would have had with two 

 boilers. To effect this, the engineer must do all he can to produce a slow 

 combustion ; and it is supposed by this slow cond)nstion a considerable 

 saving would be effected. Those of our rearlers who are conversant with 

 the mode of producing steam on the Cornish system will be more likely to 

 ajipreciate th s ; tor our entieavour is to make the two methods approximate, 

 by spreading the fuel over three sets of flues or tubes instead of two, and 

 so allowing more heat-absorbing surface. (Jne of the authors of this work 

 (Mr. Brown) had lately an opportunity of trying this plan for a short time 

 on board H.M.S. Avenger, though not long enough to obtain any measured 

 results. An order had been given to go tin with two boilers, and the fires 

 iti them were worked in the usual way, and kept in an active state of coui- 

 bu^tion. Shortly afterwards the order was given to proceed with three 

 boilers, but no additional orders were received to go on faster than with the 

 two. It was then found that it was scarcely possible to cover the fire-bars 

 in all the boilers with fuel, the rapid absorption from the great quantity of 

 surface was so effective in keeping up the steam. The saving of fuel was 

 very great, hut the limited time of the trial would not allow the actual quan- 

 tity to be ascertained. If difficulties should arise, when using large boilers, 

 in obtaining a small supply of steam — that is to say, if it be found that 

 when all the fire-bars are covered too much is generated, let one or more 

 fires in each boiler be put out, and their asb-pit doors closed, so as not to 

 allow the cool air to enter. And in using the boilers in this way the a^hes 

 may be repeatedly burned over again, merely throwing the clinkers away. 



f'hapter IX. contains Miscellaneous Rules for calculating the 

 Power of the Etigine, the Screw, &c. 



We wish the autliors would in a future edition illustrate their 

 rules with plain arithmetical computations, without having occa- 

 sion to refer constantly to a hook of logarithms. Most of the cal- 

 culations could be done in simple arithmetic as easily as with lo- 

 garithms; it would save the necessity of being obligetl to refer to 

 tables which are not always at hand. 



A Treatise on the Law of Dilapidations and Nuisances, By David 

 Gibbons, Esq., of the Middle Temple, Special Pleader. Second 

 Edition. London: Weale, 1849. 



Mr. (iibhons has retained the old title of his book as the one 

 best known to the profession; but in order to make it a complete 

 body of law for architects and surveyors, he has added to it the 

 law of Highways and Sewers. This book was before received as 

 the professional authority, but it is so much extended and amended, 

 and its value has been so much increased, that its reception is in- 

 contestable. It is needless for us to say anything in its recommen- 

 dation, for its character as an accurate compilation depends upon 

 the reputation of the author, tested by the orig-inal work. 



