This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
I have been accustomed to exclude frost from my only erection, a cold pit or frame, for three winters, by a very simple and inexpensive piece of apparatus, an account of which may be useful to some one of your readers, who, like myself, cannot avail himself of anything more costly in the way of a heating apparatus. It is simply this - a ,tin box nine inches square, the top made to lift off and put on like the lid of a canister, air-tight.
This is fixed in one of the front corners of the pit; a small pipe enters the bottom of the box, a quarter of an inch in the diameter of its bore, and an inch tin pipe runs from near the top of the box along the front of the pit, going through the end wall where it makes a turn upwards for six inches. The lid is taken off by a stout flange which runs along the sides, and the top is flat; on this a plate of iron twelve inches square, and about a quarter of an inch thick, is laid, which, when heated, gives off heat enough to keep up the temperature quite sufficient to preserve the plants from injury during a sharp frost, as I have several times experienced. The heating is effected by burning three or four night-lights (such as are sold in boxes,'and consist of a wick passing through a thin slice of cork). A small tin vessel is placed inside the box, and serves to hold the oil: when lighted it will burn all night without any further attention. As there is no door to the apparatus, it is impossible for any injurious (rases to escape inside the pit; the lid fits on tightly, and the air which circulates along the pipe enters through the bottom of the box at one end of the pit and passes out at the other, affording additional warmth, while little or no heat is lost.
The cost of maintaining it in action is very trifling, and I have been able to preserve my plants beyond my expectation. - T. R. W.