WATER TUBE BOILERS. 609 



(7) The heating surface is certanily greater in ijroportion to the 

 grate area than any other boiler, except the locomotive boiler, but 

 it can be contained in a compact volume. 



(8) The records of trials already given will show that this 

 contention is false. 



These stupid objections would not have been recorded were it 

 not that the writer is continually hearing them. In a paper 

 recently read before the Institution of Xaval Architects, Mr. J. T. 

 Milton, chief engineer surveyor to Lloyd's Registry of Shipping, 

 sums up the advantages of the water tube boiler as follows : — 



It gives (1) "the means of obtaining higher Avorking pressures 

 than are practical with other boilers, owing to the excessive thick- 

 ness of plates which would be necessary both for shell and also for 

 the heating surfaces." 



(2) " Economy of maintenance due to the comparative ease with 

 which, in some designs, every part of the boiler, both external and 

 internal, can be examined and cleaned, and, if necessary, renewed, 

 it being with some types possible to entirely re-boiler a vessel 

 without opening decks, &c." 



(3) "A decrease of space required and also of weight of boilers 

 and accessories necessary for producing a given power obtainable 

 with a given weight and in a given space." 



(4) " It is also generally claimed for all classes of Avater tube 

 boilers that they are less liable than ordinary boilers to derange- 

 ment or damage through accident or neglect, and also that, even in 

 the case of rupture, the damage which would result would be less 

 than with ordinary boilers, owing to the much less quantity of 

 water which they contain." 



Then, with reference to the important question of durability, he 

 says, "It is well known that few have become worn out in less 

 than ten or twelve years, when treated with ordinary care, while 

 many cases are within our knowledge of such boilers being now in 

 use after twenty years' service." 



It will be seen from this that almost all the factors that go to 

 make up commercial economy will tell in favor of the water tube 

 boiler for use in the marine. It allows — 



(1) Of high working pressures and consequent coal and water 

 economy. 



(2) It is cheap to maintain and can be easily renewed. 



(3) It takes up less space than other boilers ; consequently its 

 price should be credited with the saving in cargo bunkers, which 

 factor alone would repay a considerable first cost. 



(4) It is safer to work with. (And we might go on to add some 

 points which have been brought out in the former part of this paper.) 



(5) Salt water can be used in the feed with impunity. 



(And in the case of the Shann boiler, at least,) 



(6) The first cost is less than that of any other boiler of the 

 same size ; and 



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