same pressure at which it rose. I cannot make it speak, but I can make it play beautiful rythmic music. "Make me free in the seating, and about the spindle, poise me true on my centre," says the valve, “and as the steam rushes from imprisonment in the boiler to enjoy the freedom of air at the top of the waste pipe, winding its spiral and wave-like motion through my double orifice, you will hear my melodious voice singing the song of molecular freedom." Indifferent must be the man; cold the heart, and dead must be the soul of him who could not admire the grandeur of the structural "idea" of this valve.

And now, Mr. Editor, as I pass from my own valve to that of other valve mechanism, let me say a few words of gratitude. To the mental intrepidity of that most unwearied of all Government officials, Mr. Thomas Gray, I am indebted for the wisdom of his councils and the kindness of his words, always bringing encouragement in their train. From first. to last they have stimulated me to produce the valve in its present state of perfection. Shipowners also are indebted to him for the sagacity he displayed by the rapid manner in which he adopted a new and novel design, conferring a large benefit on steamship owners; and to the chief surveyor, for he also granted my very first request. To yourself, also, Mr. Editor, are we all indebted, for you were early in the field with your offer of £100 prize, stimulating the inventive faculty of the country to produce a safety-valve, which would help, in some degree, the depressed state of the shipping interest; although, owing to a small mishap of the fitter, I did not get your prize, a burr on the spindle produced by the key which receives the padlock, being driven in from the wrong side of the taper, thereby creating friction on the spindle, by burring up the top edge of the key way, and preventing the valve from rising and falling freely. This it was which made the arbitrators say something was sticking inside; but I was confident I had the best valve, because no living man had reasoned the subject in the same philosophical spirit, and that the trade of the country would fall into my hands.

THE SAFETY-VALVE AS IT OUGHT TO BE LOOKED AT BY THE BOARD OF TRADE.

No pair of ordinary safety-valves, at or about 60 lbs. pressure, of the dimensions prescribed by the Board of Trade rule, and loaded direct by a spring of the necessary strength to secure safety, will carry away all the steam generated by the fires, without an accumulation of internal pressure, which materially affects the safety of the boiler. point, the shipowner can sit in his easy-chair, for the whole responsibility of fixing the limits of pressure in the boiler is thrown by the

Legislature on the Board of Trade; and its anxiety and care for the safety of the public, demand that it should know the exact nature of that responsibility. For that purpose, it must know the conditions of construction and quality of material of which the boiler is made. It can then tell what pressure that boiler can carry with safety, and it generally assigns that pressure; and it purchases from the builder the responsibility of the safety of that boiler. The bargain is a fair and legitimate one on both sides. But if, after having got the responsibility fairly strapped down on the Board of Trade's shoulders, he (the builder) turns round and asks for 10 per cent. of accumulation, he pilfers from the Board of Trade "till," he takes that which is not his own, and for which he never made fair bargain. The scales no longer stand in the state of the balance, and he is no longer a just man of business, for he has given light weight to the Board of Trade. He has no more right to take 10 per cent. of accumulation of pressure than the grocer has to give 14 ozs. for 1 lb. avoirdupois. The behaviour of the two is identical, and were I the Board of Trade, I would not grant one ounce of accumulation of pressure. For, so long as there is a given pressure assigned, and given strength of boiler to withstand that pressure with safety, so long will the position of the Board of Trade on the one hand, and the builder of the boiler on the other, be clearly defined. But let accumulation be given or taken, and both parties have entered on the region of chance, where all is uncertainty.

ON THE SAFETY-VALVE AS IT OUGHT TO BE LOOKED AT BY A
STEAMSHIP OWNER.

Supposing the Board of Trade to allow no accumulation of pressure, or 10 per cent. of accumulation, so imperfect has the safety-valve been, that none would pass the test, even at the latter quotation, when loaded by a spring of the proper strength. But in order to pass muster with the surveyor, some engineers apply a very broad-faced valve (face broad) in order that when the valve lifts from its seat the steam will act on this broad face and help it up against the increasing resistance of the spring, and so keep the accumulation below the 10 per cent. at present allowed by the Board of Trade. (I say at present, because I trust it is only provisional on the part of the Board of Trade.) This is a most heartless valve-heartless, because it is made utterly regardless of the interest of the shipowner. This valve may just save its bones by having an accumulation of only 8 or 9 per cent., but it will lower the pressure in the boiler 16 lbs., or 26.7 per cent., when blowing off at 60 lbs., lowering the water in the gauge-glass about 2 inches before it will close; and between the time of opening and closing, a ton weight of coal has been

D

blown out at the waste-pipe and lost to the shipowner. The valve is shown on its seat at Fig. 14.

Take for example a double-ended boiler 24 feet long and 13 feet diameter.

Let the chord of the arc formed by the junction of the water and steam space be 12 feet. Let the engines be suddenly stopped and the valve blow off at 60 lbs. It will reduce the pressure 16 lbs., or to 44 lbs. when it comes to its seat, and during this time the water in the boiler will have fallen 24"; and since 1 lb. of coal evaporates about 8 lbs. of water, it follows that the number of pounds of water lost in the boiler, divided by 8, will represent the number of pounds of coal blown out at the waste pipe. With the dimensions we have selected it will stand thus, taking 62 lbs. of water to the cubic foot :

24 × 12 × 21
12

54 × 62
8

= 418.5 lbs. of coal blown from one boiler.

If there be 4 pieces of boiler on board ship, then 418.5 × 4 = 1674 lbs. of coal is lost every time this type of valve rises from its seat. But this is not its worst phase on board ship. Supposing one or more of these valves to blow off when a ship has just got under way leaving England and bound for China, this valve would blow continuously to the end of the voyage, unless the engineer let his steam down to, or below 44 lbs. Nor have I gone minutely into its waste of coal, because in lowering from 60 lbs. to 44 lbs. the temperature of the whole body of water in the boiler has been lowered by 16 degrees, and this would add about 500 lbs. more weight of coal blown away every time this valve rose from its seat. It is a thorough "spendthrift;" but shipowners can prevent it by speci

fying to their engineer that 2 lbs. must be the greatest difference they will allow between the greatest and least pressures during the Board of Trade tests. This is not an impracticable quantity, for I am willing myself to be confined to one-half of it, but more than this is bad. If on the side of accumulation, it is unsafe, and if on the side of reduced pressure, waste of coal, the interest of the Board of Trade and the shipowner is indissolubly bound up together on this subject, that which is good for one is good for the other, and that which is bad for the one is bad for the other. Herein is wisdom. Let the Board of Trade say, "I will allow no accumulation;" and let the shipowner say, "2 lbs. is the limit I will allow between the greatest and least pressures," during the Board of Trade tests, and the safety of the public and the dividends of steamship companies will be benefited thereby, in addition to which all persons concerned will have peace and comfort.

This brings me now to consider the most wretched and worst of all forms of safety-valve mechanism-the lever and dead weight, this scion of the "evil one" let loose from his chains. He has been stalking through the ranks of engineers enrobed in lamb's clothing, but with the subtlety of the serpent in his heart. This diabolical instrument, this king of boiler bursters, this monster of iniquity, this wholesale murderer, dealing death and destruction to all points of the compass, enshrouded in the cloak of innocence, has been intrusted to guard the most dangerous positions to society, and under the same covering he has been admitted to take part in the deliberations of learned men.

Fig. 12 shows this piece of mechanism as applied by the president of the Institution of Engineers and Shipbuilders of Scotland. There it stands with its fiendish hand over that hole in the boiler, proclaiming safety to all around, but death and destruction are in its heart. Beguiled by its fair external appearance of respectability, even engineers confide in its promises. But the eye of the thinking man is also upon it, and he sees through its now well-worn and threadbare habiliments, and descries the dry bones within. Let us examine it with its assumed robe of righteousness. Let us follow Mr. Robson, who called several eminent engineers of Glasgow and London to see the performance of this wolf in sheep's clothing in order to force it on to the Board of Trade.

"Oh! wad some power the giftie gie us

To see oursels as ithers see us."

This valve, with the lever and dead weight, was loaded to blow off at 35 lbs. and rose to 46 lbs., closing again at 33 lbs., 31 per cent. of accumulation, difference between the greatest and least pressures, equal to 40 per cent. With the lever and spring at the end of it and the valve loaded to blow off at 35 lbs., under test the pressure rose to 49 lbs., or 40 per cent. of accumulation, and the president of the institution considers this good behaviour, and that no better need be expected or desired by the Board of Trade and Marine Engineers. This valve, containing 17.72 square inches, applied to 19.5 feet of grate, nearly double the size prescribed by the Board of Trade rule.

But this is the valve as seen with his clothes on. Let us unrobe him of his seeming righteousness and dissect the skeleton inside, which lies hid from the casual, but not from the mental observer. See Fig. 12. V is the valve, fitting in its seat by 4 feathers as shown, and the spindle is cast solid with the valve, both being one casting. C' is the junction. of the lever and spindle, and C is the stud which receives the end of the lever, and which is a fixture immovably set in the structure, and with the weight or spring balance attached to the long end of the lever. Let us now get steam up until the pressure is capable of producing motion of the valve. The path of the valve is along the centre line of the seating and spindle, along C' D and is a straight line; while the path of the lever, which is rigidly bound to the valve at C', and rigidly bound to the structure at C, is a radial line C' E about the centre C.

Now I tell Mr. Robson that if the fittings of this valve be good it cannot possibly lift" from its seat, whatever be the pressure beneath it. It is a physical impossibility for it to lift higher from its seat than the play or clearance of the feathers in the seating will allow. The valve will just lift to a height represented by the clearance in the feathers forming the versed line of an arc along C' E, and the semi-chord