PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 867 



strong material for boilers ; yet it will be seen in the form of 

 spheres as now described it aiibrds greater absolute strength 

 against bursting than is possessed by any form of plate iron 

 boiler." 



If, therefore, Ave can employ a group of such cast-iron spheres 

 united, and of a maximum capacity adequate to any standard of 

 duty required, so much of the problem is solved. For it is clear 

 that by such enlargement we will not be compelled to strengtheji 

 the whole nor any part of it, for having adequate strength in a 

 single sphere to resist any required pressure, a multiplicity of 

 such spheres, to any extent, may be used with like security. 



The fractures that have occurred with the spheres of tihis boilef 

 have been on the top of a transverse neck of a unit, being simply 

 a crack, in central line, between the globes, and from three to live 

 inches long. From this fissure the steaiui or water, or both, issue 

 as a film only. 



If the contents of the boiler be permitted to escape by the 

 fissure the fires will be extinguished, but if the 'fires are drawn, 

 the steam relieved and the water blown oflf, a few hours only are 

 necessary to replace the fractured unit by a new one, and the 

 work of the boiler ijoes on as usual. 



No accident, of any nature, has ever occurred to person or pro- 

 perty from any of those boilers, even when fracturing under high 

 pressure. Engineers soon learn that no danger can arise from the 

 boiler, and this has, in some cases, caused too much reliance on 

 its strength, and led to imprudence or neglect. In a case not long 

 since, in this city, a globe was cracked from negligence, under 

 extreme pressure, the engineer volunteering the admission that a 

 similar case with a wiought-iron boiler would have blown the 

 place to atoms. 



There are more than 12,000 horse power of these boilers in 

 daily use, varying from 10 to 300 horse power each, and all set 

 up within two years past, yet it is eight years since the invention 



w^as practically and satisfactorily tested. °^ 



■» 



Franklin Institute Experiments. 



Some experiments were made during October last, before a 

 committee appointed by the Franklin Institute, for testing this 

 boiler. Their report embraces the following : 



First, of a section 78 spheres raised to the position as set up for 

 use, ruptured under cold water pressure in the lowest pair of 



