218 GREENHOUSE CONSTRUCTION AND HEATING. 
time the cement facing should wear or break away to the 
brickwork, put on a fresh coat at once, and don’t touch it till 
set quite hard again. 
It is far cheaper in the end to construct a good sound and 
tight stoke-hole at first than to have to keep on constantly 
pumping afterwards, not to mention the risk of the water 
rising badly some possibly frosty night and putting out the 
fire, probably with disastrous consequences. 
Notes on Fuel and Stoking.— Ordinary gas-coke, 
broken up more or less small, according to the size of 
the furnace, is usually employed as fuel for most. 
descriptions of greenhouse boilers and furnaces, and 
being at once inexpensive and almost entirely smokeless, 
it is on the whole very suitable for the purpose. Common 
coal, though affording considerably more heat, is quite. 
inadmissible, owing to the amount of smoke and soot 
it produces, which, apart from the nuisance, would render- 
the flues, etc., constantly foul. Good coke, free from 
clinker, and broken up small—in pieces about the size. 
of hen’s eggs—forms the best of all fuels for all 
the small independent slow-combustion stoves (boilers) 
described on pp. 196-8, coal of any kind being useless 
for these. In large furnaces the coke may be fed in 
large lumps, or rough, as it comes from the gas-works, 
or nearly so. Specially prepared, or oven-coke would be 
a decidedly superior fuel to gas-coke, as affording more 
heat, but its cost renders this out of the question. 
Of late years the anthracite or Welsh smokeless coal 
has been employed as fuel for horticultural purposes to. 
a considerable extent, and its use is steadily, if not very 
rapidly extending. Its advantages are that it gives a. 
