equence would be equally dangerous, for the water that was in the
glass before the stoppage occurred would remain in it, for the stoppage
would not allow it to drop down into the boiler again; so there it would
remain, and when the stoker came round to look at his boiler, unless he
happened to notice that no movement of the water was visible, he would
pass on without further ado, and remain in total ignorance of his
danger. Hence the necessity for the stoker to blow out his water gauge
every time he comes in front of his boiler, and if the water enters the
glass in a sluggish or dilatory way the cocks need to be cleared of the
partial stoppage, and let the water enter the glass with a rush.

23. _Question._--Could a boiler collapse without affecting the fusible
plug?

_Answer._--Yes; the tank that supplied the boiler with water leaked
badly, and to stop the leaks a quantity of fine oatmeal was mixed with
water and poured into it, and in due time reached the boiler; but
instead of the oatmeal permeating the whole of the water in the boiler,
it never got beyond the parts surrounding the fireplace; it stuck on the
sides and top thickly, and was baked hard on them. After a few days the
sides of the fire-tube bulged inwards nearly twelve inches, and the
boiler had to be stopped and blown out, and the fusible plug was found
to be unaffected--it was one selected by a Boiler Insurance Company, who
had to repair this damage, and the stoker was exonerated from blame, but
there is little doubt that if the plug had leaked the mishap would have
been attributed to shortness of water and the stoker would be blamed for
what he did not do, and get the sack into the bargain.

24. _Question._--Why is it that an injector can force water into a
boiler from which the steam comes to work the injector at a greater
pressure than is in the boiler?

_Answer._--The secret of the working of the injector is due to the
velocity of the steam issuing from the point of a conical tube, and
water issuing from another conical tube somewhat larger than the steam
cone, and a partial vacuum created in the barrel by the steam and cold
water meeting--as both cones face each other. The cones are about four
inches long, one and a quarter inch wide at the mouths, and about one
half of an inch at the points. The suction pipe, steam pipe and delivery
pipe are about one inch diameter, and the overflow pipe half an inch
diameter, and the water tank three feet b