1842.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



367 



Length of stroke of engine in feet = 5- 

 Speed of the piston in feet per minute = 213- 

 Total weight of rim in lb. = 5000- 



Mean circumference of the rim in feet = 47'1 

 Then by formula 8. 



/^ 7,987,500-;- (^^^ X 213) = 27-4 = speed of the rim in 



feet per second, and ^-~~ = 34-90 = nearly 35 revolutions 

 per minute. 



For corn-mills, &c., this formula would only vary by reducing the 

 constant number 7987500 as stated above to 5591250. 



therefore ^5591250 -^(g|_X 213) = 22-9 = speed of rim 



in feet per second, and ^Hl^GO ^ ^^ ,e^„,„ti„„^ p^^ ^j^^^^^ 



That IS to say, that for machinery requiring regularity, the fly- 

 wheel applied to a 20 h. e. should make 35 revolutions per minute, 

 but if required to drive machinery for which regularity is not neces- 

 sary, the same wheel need not make more than 20 revolutions per 

 mmute. "^ 



Formula 7 and 8 are obtained by reversing formula 6. 



London, Ochber IIM, 1842. H. H. Edwards. 



NOTES ON STEAM NAVIGATION. 



The management ef the furnaces. —It is a common practice in steam 

 vessels to pile the coal much too abundantly on the fire grate, the 

 stratum of incandescent fuel is too thick, and the generation of car- 

 bonic oxide is the consequence, to the manifest diminution of calorific 

 effect. The coals should be strewn upon the grate bars evenly and 

 equally ; the depth of the stratum should be about three inches, but 

 this is a point dependent in a great measure upon the intensity of the 

 draught ; the stronger the draught the thicker should be the stratum 

 of incandescent fuel. The bars should never exceed 7 feet in length, 

 and should be as much less as possible ; 6 feet is a good length, and 

 not an uncommon length in the best boilers. It is impossible to fire 

 long furnaces properly, especially in a sea way. We have known the 

 length of the fire bars to be reduced from 8 ft. 6 in. to 5 ft. G in. with 

 a great accession to the steam-producing powers of the boiler. The 

 bars should always have a considerable inclination, both to facilitate 

 the transmission of the fuel from their foremost to their aftermost 

 extremity, and to diffuse the air more equably over their lower surface. 

 The skill of firemen varies greatly, and due attention should be paid 

 to their selection. A dead plate at the mouth of the furnace is a 

 good thing, and combined with a slow combustion will obviate smoke 

 and save fuel. These are the true secrets of combustion on chemical 

 principles. 



Boilers, near and /car.— The wear of boilers is not unfrequently 

 chiefly from the outside round the steam chest, from the dripping of 

 -water from the decks, in the ash-pits from the wetting of the ashes, 

 and on the bottom of the boiler from the action of the bilge water. 

 This last source of wear is now almost altogether obviated in some of 

 the best steam vessels, by placing the boiler upon an eflicient caulked 

 platform, bedding it in putty— not an incorporated mass of lime and 

 oil, but really sound substantial putty, such exactly as glaziers use. 

 A cooming of timber is attached to this platform, encircling each 

 boiler, and the interstices between the timber of the cooming and the 

 iron of the boiler are filled in with roman cement, and sloped off on 

 the upper side, so that no water can lie on the cement or cooming. It 

 Might be expected that these coomings would be disturbed by the ex- 

 pansion of the boiler when heated, but we find that the expansion is 

 so inappreciable in practice as not to be productive of any visible 

 derangement. The upper parts of boilers should be covered with felt 



and sheet lead, soldered wherever there is a joining ; the practice of 

 covering boilers with felt and sheet lead is now almost universal 

 among the best engineers. 



Blom-off cocks are a perpetual source of annoyance if they be not 

 well made at first. The metal of which they are composed should be 

 hard and tough, without any lead in it. The plugs of the cocks, if 

 made with too little taper, will be very apt to jam, and after having 

 been ground a few times, will sink so far into the socket as to come 

 in contact with the bottom, if there be one, and diminish materially 

 the effective area of the water way. If the taper be too little on the 

 other hand, a great strain will be thrown on the gland, which keeps 

 the plug in its place, and if they give way it will be driven out with 

 great force. This did occur in the Great Western, and the engineer 

 was scalded to death. 



The durability of brasses is dependent upon a variety of circum- 

 stances, but chiefly upon the quantity of rubbing surface and the 

 quality of the metal. We have seen a brass of Boulton & Watt's 

 which had worked for thirty years, and was at the end of that time in 

 good preservation, whilst we liave seen other brasses which, in the 

 course of a couple of years, were quite worn out. 



De omnibus rebus et quibmdam aliis. — Should the engineers be sub- 

 ject to the captains ? Ingenerals, YES— in particulars, NO. The Ad- 

 miralty regulations in reference to engineers are just as preposterous 

 as might be expected, inasmuch as the Admiralty is invariably a cen- 

 tury behind the merchant service, but in their regulations respecting 

 engiueers, they have out-Admiraltied themselves and earned a title 

 to a squabash with our tomahawk, with which we may probably 

 honour them on an early occasion. The Admiralty desires to have 

 young men of education as engineers, and yet with Admiralty consis- 

 tency rates the engineer beneath the ship's carpenter— and what engi- 

 neer of talent and education would place himself in so abject a situ- 

 ation, or submit to be snubbed and brow-beaten by every whiffling 

 lieutenant or embryo midshipman who does not know the garboard 

 streak from the log line ? As to your amateur mechanics, we always 

 shun them as carefully as we would do a rabid dog; their bite is dan- 

 gerous, and their bark— why that of Cerberus was heavenly music to 

 it. We have never recovered from the alarm we once experienced 

 from the spectacle of one of these cognescenli with blackened fustians 

 and white kid gloves, crawling daily, for the space of a whole week, 

 through the labyrinths of an oily steam engine, to vindicate his title 

 to engineering proficiency. We bethought ourselves of Nebuchad- 

 nezzar, and betook ourselves out of reach of the saliva. When we 

 take upon ourselves the administration of the Admiralty, which, be- 

 tween this and 1942, we may perhaps be prevailed upon to do, our 

 first operation will be to get a leviathan besom constructed to sweep 

 away all such incurables preparatory to placing engineers in their 

 proper position. 



Ventilation is a thing greatly neglected in steam vessels, although 

 so many facilities exist for establishing an effectual system. Every 

 vessel should be fitted with one or more fans, or Day's patent Archi- 

 medean Screw ventilator, worked by the engine for exhausting the 

 air from the different cabins, gratings being left above the doors and 

 in other suitable places for the admission of fresh air from without. 

 The same mechanism might be made to draw air from the holds and 

 other parts of the ship, so that any bad smell from bilge water, &c. 

 would be entirely obviated. In tropical climates, in particular, no 

 steam vessel of any considerable size ought to be unprovided with a 

 ventilating apparatus. 



The rolling of steam vessels in a sea way gives a lateral impulse to 

 several parts of the machinery, which it is often not well calculated 

 to resist, without a considerable jolting. Thus the side levers will, 

 when the vessel rolls heavily, slip in and out upon the main centres, 

 and the shafts will move endways. It is true there are collars to pre- 

 vent this, and in new engines no great movement of this kind can take 

 place ; but the collars are in most cases much too small — they are 

 deficient in rubbing surface, and they consequently wear, in a short 

 time, considerably into the brass, leaving a lateral play upon the jour- 

 nal which admits of no adjustment. To obviate this evil, Messrs. 



