Polytechnic Association Proceedings. 717 



The strong circulation prevents the deposit of s'^climent in the 

 tubes, and increases their eifect. The facility with which they can 

 be cleaned and kept clean, both outside and inside, enables its 

 economy to be maintained even after long use, which is well known 

 is not the case with the ordinary form of boiler. 



The lodgment of ashes, soot, &c., in the concave surfaces of the 

 flues and tubes of common boilers, reduces the economy of these 

 forms greatly. 



This is especially the case where the fuel used produces a large 

 amount of ashes and dust, as in shavings, saw-dust, spent tan bark, 

 <fec. In the safety boiler the ashes can lodge upon but a very small 

 part of the convex top surface of the tubes, and the draft will 

 sweep this oif quite efl'ectually. A steam jet will keep the outside 

 of the tubes perfectly clean. 



In every case where it has replaced other boilers, or put to the 

 same work, it has shown the most remarkable econom3\ 



It is a very rapid generator, raising steam to start the engine in 

 twenty to thirty minutes from cold water, while many boilers 

 require from one to two hours. 



DURABILITY. 



Much that has been said on the subject of safety also applies 

 here, and is not repeated. 



The destructive action of irregularity of expansion and contrac- 

 tion, which is constantly at work in all other forms of boilers, does 

 not take place in this, as any two or more tubes, lying side b^" side, 

 expand and contract nearly equally; still, any inequality would have 

 no bad effect, owing to the manner of attaching the parts together. 

 It is this force that, in the ordinaiy boiler, is always tearing the 

 tubes loose where they are expanded into the tube sheets, loosening 

 rivets along seams, and throwing an enormous strain upon all pai*ts 

 of the boiler, thus explaining many explosions. 



The safety boiler has no narrow, inaccessible water spaces or 



' legs," as in the locomotive or upright tubular, where the sediment 



settles, often causing burning of the plates and explosions. This 



is an important element in its durability, as all who are familiar 



with the frequency of " soft patches," &c., will understand. 



The question may be asked: Are the tubes as used in the safety 

 boiler as durable as they would be in other boilers ? "We think 

 they are much more durable, as the fire does not attack the ends 

 as severely as in the locomotive or upright tubular boiler, for 



