858 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



strength against internal pressure; and it is clear that a multipli- 

 city of such spheres can maintain this unit of strength; hence, it 

 follows that a steam generator on this system may be increased to 

 any extent, without weakening the whole or any part of it. 



Over 150,000 of such globes have been put in practical use of 

 which number a proportion equal to one in 5,000 have cracked, 

 from all causes, which, considering that it embraces the life of the 

 enterprise, with inexperienced parties and hazardous tests, should 

 be regarded as almost nil. 



Secukity of the Joints. 



To compensate for irregular expansion under heat, and prevent 

 binding or disturbance of the parts, the transverse steam and water 

 pipes described, are composed of short pieces with spherical joints, 

 and screwed together with tie bolts, as with the units. 



If the heat acted alilie on the cast iron spheres and the wrought 

 iron tie rod, the latter, expanding the most, would tend to slightly 

 separate the joints, but this difierence is usually compensated by 

 the globes being at a higher temperature than the rod, so that the 

 joints are kept close. It sometimes occurs that a joint may show 

 a leak for a few minutes when the pressure is low, particularly 

 after a higher pressure, but it will close as the steam rises, from 

 the expanding of the spheres by increased heat. 



Those leaks, however, are of no appreciable detriment to the 

 duty of the boiler, as they rarely exceed the amount lost by the 

 ordinary escape from a safety valve. Indeed the joints of this 

 boiler may be all made safety valves, due in a chief degree to tho 

 tension placed on the tie rods by the fastening nut, and to ths 

 pressure of the steam. 



I recently inspected a Harrison boiler of 266 horse power, at 

 the sugar refinery of Messrs. Newhall, Borie &, Co., in Philadel- 

 phia, which, for more than a year past, has l)een subjected to most 

 severe usage, carrying 80 pounds and upwards of steam, and so 

 fired for the duty required of it, that the furnace looked more like 

 one for smelting iron, than for a steam boiler — the bricks being 

 vitrified and run down like stalactites, and yet there was not the 

 slightest leak of water or steam. Yet this boiler contains nearly 

 4,000 joints. This firm has ordered an additional Harrison boiler 

 of 100 horse power, 'to be put up in the same w'orks in May 

 next. 



