ON THE DEVELOPMENTS OF MECHANICAL ENGINEERING. 499 



the ash-pit itself. The other marine engine to which I wish to call 

 your attention, is one that has been made with a view to great economy. 

 The principles followed in its construction are among those suggested 

 by the President (Sir W. G. Armstrong) in his address. He — you 

 will remember — pointed out that the direction in which economy in the 

 steam-engine was to be looked for was in that of increasing the initial 

 pressure ; although, at the same time, he said, there were drawbacks, in the 

 shape of greater loss by radiation, and by the higher temperature at which 

 the products of combustion would escape. "We must admit the fact of the 

 latter source of loss when using a very high pressure of steam, it beino- 

 inevitable that the temperature of the products of combustion escaping 

 from a boiler under these conditions must be higher than those which 

 need be allowed to escape when a lower pressure of steam is employed ; 

 although I regret to say that in practice in marine boilers, working at com- 

 paratively low pressures, the products are ordinarily suffered to pass into 

 the funnel, at above the temperature of melting lead.' But with respect 

 to the loss by radiation in the particular engine I am about to mention — 

 that of Perkins — there is not so much loss as that which prevails in the 

 ordinary marine boiler, because the Perkins boiler is completely enclosed, 

 with the result that while there is within the case a boiler containino- 

 steam of 400 lbs. on the square inch, and the fire to generate that steanT, 

 the hand may be applied to the casing itself, which contains the whole of 

 the boiler, without receiving any unpleasant sensation of warmth. By 

 Mr. Perkins' arrangement, using steam of 400 lbs. in the boiler, it was 

 found, as the result of very severe trials conducted by Mr. Eich, of 

 Messrs. Easton and Anderson's firm, and myself— trials which lasted for 

 twelve hours — that the total consumption of fuel, including that for 

 getting up steam from cold water, was just under 1-8 (actually 179) ' 

 lbs. per gross indicated horse-power per hour. That consumption was 

 ascertained in a manner which it is desirable should always be employed 

 in steam-boat trials. It was not arrived at by using as a divisor the 

 horse-power of the most favourable diagram obtained during the day, 

 but it was got from diagrams taken every half-hour during the regular 

 work ; then, when the pressure began to die down, from coal being no 

 longer put upon the fire, diagrams taken every quarter of an hour ;'' and 

 then, towards the last, every five minutes ; and the total number of foot- 

 pounds were calculated from these diagrams, and were used to obtain the 

 gross indicated horse-power. 



Furthei-, so far as could be ascertained by the process of commencino- 

 a trial with a known fire, and closing that trial, at the end of six hours', 

 with the fire as nearly as possible in the same condition, the consumption 

 was 1-66 lbs. of_ coal per gross indicated horse-power per hour, so that, 

 without taking into account the coal consumed in raising steam from 

 cold water, the engine worked for If lbs. of coal per horse per hour. I 

 think it well to give these details because, undoubtedly, this is an ex- 

 tremely economical result. 



Our President alluded to the employment of ether as a means of 

 utilising the heat which ordinarily escapes uselessly into the condenser, 



» It should have been noticed, that although the products of combustion must 

 escape from the boiler at a greater temperature where a high pressure of steam is 

 employed than they need escape at where a lower pressure is used, it does not follow 

 that loss should accrue on this account, as the excess can, by means of a heater, be 

 taken up by the feed water : a plan Mr. Perkins is employing in practice. 



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