PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 859 



Circulation of Heat. 

 In this condition we have a series of spheres combinetl for the 

 evaporation of water, and so made up as to admit of an unprece- 

 dented proportionate area of grate bars and furnace, as well as a 

 corresponding increase of capacity for the circulation and mixing 

 of the products of combustion, which, in their transit to the chi'tn- 

 ney, gyrate among and envelop all the globes; each of which being 

 'a steam generator, holding only a gallon of water, presents its 

 entire exterior of 198 square inches to the heat; or about 50 inches 

 to each quart of Avater. Indeed, so complete is the combustion, 

 and so thorough the absorption of heat, that but 350° are often 

 found in the flue of the chimney. 



Circulation of Water. 



A peculiarity that should not be overlooked is, that the heat 

 first impinges against this boiler, as usually arranged, nearly at 

 the tap of the water line, instead of at or near the bottom, as with 

 ordinary boilers; and from that line it sweeps through the group 

 upwards, and then turns downwards to the bottom of the boiler 

 which takes the last and most exhausted temperature where the 

 water is coldest. 



This would at first seem to impede proper circulation, as it 

 readily brings to mind the operation when a test tube and lamp 

 are skilfully manipulated. If the lamp is held to heat the bottom 

 end of the tube, the fluid will be violently projected from the 

 vessel and lost ; but when the heat is made to act at a point near 

 the top of the fluid, ebulition will proceed satisfactorily, but there 

 will be no perceptible circulation. 



Circulation in this boiler, however, is eflected by the steam 

 rising from the lower globes to the higher, each ascending series 

 of globes being further removed from the seat of the greatest 

 heat. The upper globes are not reached until the heat has tra- 

 versed the width of the section in a diagonal line, and the water 

 being at a lower temperature in the higher than in the lower 

 series of globes, it rushes down, around, and into the spheres which 

 are sending out the largest volume of steam. A circulation com- 

 mon to each strata of globes, according to its measure of compara- 

 tive heat, thus insuring constant and uniform circulation, rarely, if 

 ever equaled in contracted water spaces. 



