608 PROCEEDINGS OV SECTION H. 



The boilers in the Messaijeries packet boats are worked at a 

 pressure of ISOlbs. per square inch, and there is no inconvenience 

 such as has been experienced in abnost every large boiler in the 

 British Navy from leaking of the tubes where tliey are connected 

 with the tube plate, wlien the I. oiler has been forced. On the 

 contrary, the behaviour of water tube boilers when pressed is 

 remarkable, and in this respect at least they far surpass all other 

 types. The table already given (page 605) will show that in no 

 case could the boilers be saitl to tiave primed when under their 

 capacity trials. 



There are, no dovibt, still many places where fire tube boilers will 

 be found more suitable than water tube boiles, but sufficient has 

 been said to show how much more these boilers are being used 

 than they were some years since. The objections raised against 

 this boiler were as follows : — 



(1) It is too costly. 



(2) It requires frequent overhauling for repairs owing to the 

 number and complexity of its parts. 



(3) It is troublesome to clean, being inaccessible in parts. 



(4) Its circulation is defective. 



(5) It is too weak to stand much wear and tear. 



(6) It is liable to leak owing to the large number of joints. 



(7) It occupies an exceedingly large space. 



(8) It is not economical in fuel. 

 In answer to these objections : — 



(1) Most water tube boilers are more expensive than other 

 boilers of the same capacity at the manufacturers' yard, but when 

 the boiler has to be transported any distance, and perhaps erected 

 in an inaccessible place, it often costs the owner less when 

 erected. 



(2) AVell-designed water tube boilers do not require to be re- 

 paired more than once in two or three years, and then the repairs 

 are slight, and can be effected without much trouble and in a 

 short time. 



(3) If the circulation be at all uniform it is so rapid that the 

 boiler is self- cleaning. 



(4) In a well-designed water tube boiler the circulation should 

 be better than in any other boiler. 



(5) To withstand the same steam pressure a water tube boiler 

 may be many times lighter than any other type, and consequently 

 is not subject to the same racking or straining ; in fact this is a 

 point also in which, if properly designed, a water tube boiler should 

 be superior to any other type. 



f6) There is no inherent reason why the joints should leak any 

 more than other water joints, and it has nol been found that this is 

 is a source of trouble ; some joints often leak when the boiler is 

 cold which, however, soon become tight owing to expansion when 

 the steam is beino- formed. 



