^55 



The Construction of Boilers 



a tenison-rod or bolt of wrought or malleable 

 iron bb. The diameter of each sphere is 8 

 inches, the thickness of the metal three- 

 eighths of an inch, and the internal diameter 

 of opening of the neck 3 inches. Each 

 sphere is by the inventor termed a "unit," 

 and is connected with its neighbour "unit" 

 or '• units " by the hollow neck which is pro- 

 vided with a socket and shoulder, so that a 

 steady as well as close contact is secured, 

 and round the joint thus made a steam-tight 

 iron cap is placed. What are called " slabs " 

 are made up of a definite number of units, all 

 held together by the wrought-iron rods of 

 bolts, and each slab forms a "vessel" con- 

 taining water and steam, both of which can 

 circulate freely throughout the whole range 

 of units or spheres of which the slab is 

 fonned. The slabs may be in any number, 

 according to the evaporative powers of the 

 boilers required ; and are placed side by side 

 in a furnace, and connected with the feed- 

 water pipe at bottom, and by a steam pipe at 

 top. The water-level is so arranged that 

 about two-thirds of the spheres in the slabs 

 are filled with water, the remaining third 

 acting as the steam space. The slabs are 

 not placed on the level, but, as shewn in fig. 

 ID, at an inclination. This enables the water 

 to be completely drained off when the boiler 

 is blown out, and has the further advantage 

 of bringing the greatest number possible of the 

 water-filled spheres, directly over the hottest 

 part of the fire, leaving the greatest number of 

 steam-filled spheres at that part of the furnace 

 where ebullition would be least active. The 

 principal points of excellence of this form of 

 boiler are these-^rj/, its almost absolute 

 safety ; for while the spheres have actually 

 stood the test of 1500 lb. to the square inch, 

 the practical limit may be stated thus, that 

 the " factor of safety " of a boiler of the best 

 construction of the Lancashire form, with a 

 pressure of 50 lb. only on the square inch, 

 is the same as that of a Harrison boiler at 

 250 lb. — a pressure to which, at least, no 

 agricultural boiler need ever be worked at. 

 Second, although free almost entirely from the 

 possibility of an explosion, the Harrison 

 boiler, if worked at a pressure greater than it 



ought to be subjected to, acts throughout as 

 its own safety-valve ; for, on great pressure, 

 the wrought-iron bolts or rods are so stretched 

 that the connexions or joints between the 

 spheres are so opened that the pressure is at 

 once relieved by the steam or the water 

 escaping. A Harrison boiler may empty 

 itself within such circumstances, but it can 

 scarcely be said to be liable to " burst," in- 

 volving by this term all the disastrous conse- 

 quences attendant upon the bursting of a 

 large boiler of the ordinary construction. 

 The third point of excellence is the extreme 

 portability of parts. A fourth, the readiness 

 Avith which any part of a boiler can be re- 

 newed ; and a ffth, the great advantage of 

 adding to a power of a boiler by simply in- 

 creasing the size or number of the " slabs." 

 But to these advantages we may add a sixth, 

 and this not the least important. All those 

 who have had anything to do with steam 

 boilers know the dangers and inconveniencies 

 arising from the incrustation of boilers. 

 Now, in the Harrison boiler, no — at least very 

 litde — deposit of matter or " scale," as it is 

 called, takes place ; all that is necessary to be 

 attended to is to blow out the boiler once a- 

 week — that is, if in regular work — and the 

 spheres will keep themselves quite free from 

 scale. It is needless here to take up space 

 by an inquiry into the causes of the self- 

 cleansing action of the spheres : it is suffi- 

 cient to know that they are always operative, 

 so that even Avith the use of very foul Avater, 

 Avhich Avould infallibly scale or encrustate 

 AATOught-iron boilers, no scale or deposit is 

 made in the spheres of the Harrison boiler. 

 Such is a brief description of the latest form 

 of boiler introduced, and AA-hich, according to 

 a very eminent authority, constitutes one " of 

 the most remarkable discoveries in boiler 

 engineering." 



We noAV turn our attention to the care 

 requisite to ensure safety and economy in the 

 AA'orking of boilers. An absurd Yankee story 

 is told of a man, in the course of one of 

 those steamboat races so common in the 

 Avctern waters of America, volunteering to 

 sit upon the j-^/'/j '-value — a dangerous duty 

 shirked by all on board — ^judgingashesaid, that 



