In kindling a coal fire in a furnace the phosphorus of a match inflames at so low a temperature (150 degrees Fahr.) that mere friction ignites it, and in burning (combining with oxygen of the air) it gives out heat enough to raise the sulphur of the match to the temperature of ignition (500 degrees Fahr.), which, combining in its turn with the oxygen of the atmosphere, gives out sufficient heat to raise the temperature of the wood to the point of ignition (800 degrees Fahr.), and at this temperature the wood combines with oxygen supplied by the air, giving out a temperature sufficient to raise the coal to the point of ignition (1000 degrees Fahr.), and the coal then combines with the free oxygen of the air, the ensuing temperature in the furnace varying, according to circumstances, from 3000 degrees to 4000 degrees Fahr. Thus we see that the ignition of the coal is the last of a series of progressive steps, each increasing in temperature.

And in each step it will be noted that a combination of oxygen is the essential connecting link and that the oxygen is supplied in each instance at the same average temperature—this fact contains a “point” relating to supplying furnaces with so called “hot air.”

Sawdust Furnace.

Referring also to page 33 for information relating to the burning of sawdust and shavings S. S. Ingham, in the Stationary Engineer, says upon this important matter:

“Regarding a furnace for burning sawdust, I submit the accompanying cuts. I have built numbers of these oven furnaces for burning this fuel in the south, and all have given excellent results. The dimensions are for 60 × 16' return tubular (4 tubes) boiler with stack 50 per cent. greater area than the flues; a good draft is necessary.” It will be understood that the upper cut is designed to show end view of the furnace whose side is shown in sectional view at the bottom of the page.

GAS PIPE.