Chap. 9.]

Bell Traps — Water-Lute.

563

orifice of the pipe, and consequently that depth in water; thus cutting offall external coramunication with the air in the sewer. A loose grate fitsinto a recess on the edge of the box, and is occasionally removed to takeout the dirt that passes the grate. Small traps of the kind, and made ofcast iron, are sometimes used in the drains of private houses.

No. 281 is named a bell trap from its figure. Such are generally ofsmall dimensions, and are mostly used in kitchens, over the channels ortubes through which refuse fluids are discharged into sinks or drains. Theend of the pipe projects two or three inches into the trap, consequently aquantity of water must always remain within at the same elevation. Overthe pipe a bell or inverted cup dips about half an inch into the water, andis of such a size as to leave sufficient room for the fluid to descend betweenit and the sides of the trap, and also to pass under its edge and rise intothe pipe, and so escape into the drain. The cup or bell is connected to abrass grate that drops into a recess cast round the inner edge of the trap.

The origin of traps is, we believe, unknown. The principle is preciselythe same as in the water-lute of old chemists. Glauber used contrivancesidentical with Nos. 278 and 281, instead of cocks to close retorts, &c. In-stead of water he sometimes used mercury, when the contents were of acorrosive nature.

END OF THE FIFTH BOOK.