912 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



the tubes, extending from a short distance above the water-line to 

 within about half an inch of the upper tube-sheet, fitting at its lower 

 edge the inside of the shell of the boiler, (to which also it is fast- 

 ened), and the tubes at its upper edge. It thus forms a steam- 

 chamber between the cone and the outside shell of the boiler, into 

 which the steam can only pass by going over the top of the cone. 



H H are tubes fastened into the lower and upper tube-sheets. 



K is the smoke-pipe. L is the blow-off cock. 



M is the water supply-cock. N is the steam-valve. 



W is the water-line. 



Water is run into the boiler throuG-h M to the height W, fillinor 

 all the spaces between the shell and fire-box and tubes. The fire 

 being then started in the fire-box, heats the lower tube-sheet, tubes, 

 and fire-box sheets. The water directly over the fire among the 

 tubes is, of course, heated first, and, expanding, rises over the top 

 of cylinder F, and flows over into the space between F and the 

 shell of the boiler, (the water previously surrounding tue cylinder 

 being drawn in to fill its place.) A current is thus started iip the 

 centre and down the sides, which is rapid in proportion to the 

 intensity of the heat in the tubes and fire-box. The circidation 

 causes a regular action and an equal temperature to the water, and 

 sweeps off the bubbles of steam which naturally cling to the steam- 

 making surface. The steam that is thus carried up to the cone G 

 is pure steam, i\\e. ?^a(i'e7' separating from it at the water-line and 

 passing down again with the current. It also prevents the tubes 

 from getting above the best steam-making temperature, as the 

 higer temperature, only quickens the circulation, and thus a per- 

 fect balance is kept up between the two. Thus by utilizing any 

 possible degree of heat, we obtain the greatest economy of fuel. 

 The circulation also sweeps the dirt and sediment from the wj^ter 

 off the tubes and crown sheets, and deposits them in the space 

 around the fire-box where the water is the most c^uiet, effectually 

 preventing all incrustation — a most valuable feature. The steam 

 after being delivered into the upper part of the boiler, is further 

 dried and imrified from any water which it may hold by contact 

 with the upper part of the tubes, and then passes into the space 

 between the cone and the shell of the boiler, Avhence it is taken 

 through the steam-pipe into the engine. 



This principle has been adapted to horizontal boilers, and is 

 applicable to any desired form. 



