PORTIONS OF THE MARINE BOILER WHICH BECOME THIN BY WEAR.

These are generally situated, 1st, at or a little above the line of

fire bars in the furnace; 2d, the ash pits; 3d, combustion chamber

backs; 4th, shell at water line; 5th, front and bottom of boiler.

The thinning can usually be detected by examination, sounding with a

round nosed hammer, or drilling small holes in suspected parts not

otherwise accessible for examination.