of Stoves and other Horticultural Erections. 489 



I will keep it in repair, and take the responsibility of its acting 

 properly for three or more years, provided that it is fairly used." 

 (p. 26.) The time during which such a boiler will act properly 

 will depend on three things: I. the number of times in the 

 year which it is used ; 2. the degree of heat to which the water 

 is raised while in the boiler ; and, 3. the quantity of earthy 

 matter held in solution by the water. In all cases of heating by 

 hot water, unless the water used has been distilled, a deposit of 

 earthy matter takes place on the bottom of the boiler, in direct 

 proportion to the quantity of water evaporated, and, consequently, 

 to the heat used. Hence the difference in the deposition in a 

 boiler employed to heat a stove, and one employed to heat a 

 green-house. The deposition of this earthy matter on the 

 bottom and sides of the boiler diminishes the conducting ten- 

 dency of the metal ; and hence boilers that have been some 

 months in use are never so easily heated as those that are newly 

 erected, or newly cleaned out. Boilers constructed like that of 

 Mr. Thomjison do not admit of being cleaned out ; because, to 

 be cleaned, the metal must be scraped by the hand ; and, con- 

 sequently, as, from the moment such a boiler is put up, a coating 

 of the earthy matter which is deposited begins to be formed, which 

 increases every day, after a certain point the boiler will cease 

 to be so economical as the commonest form of open boiler that 

 admits of being cleaned out readily, and is so cleaned frequently. 



In our opinion, no boiler deserves to be employed, that does 

 not admit of being frequently and thoroughly cleaned out by 

 scraping, and that with ease. We can conceive such a coat of 

 earthy matter being deposited on the bottom of a boiler as 

 would admit of the metallic part of the bottom of the boiler be- 

 coming red-hot ; and every engineer knows that this does happen 

 sometimes, when an explosion is the never-failing consequence. 

 Gardeners, therefore, ought to be strongly impressed with two 

 facts : first, that, whenever a boiler is in use, a constant depo- 

 sition of earthy matter is taking place on its bottom and sides 

 every day ; and, secondly, that unless this earthy matter be con- 

 stantly removed as it accunudates, the heating powers of the fuel 

 employed will be greatly diminished. 



We shall take no farther notice of this pamphlet, than to 

 express our regret that Mr. Thompson has published it; for, to 

 those who know anything of the diffi^rent subjects which are 

 men.tioned in it, it exhibits a degree of ignorance and presumption, 

 that one would hardly have considered would have been given 

 utterance to in the present day. We can only account for it by 

 supposing (what, indeed, is but too obvious) that Mr. Thompson 

 does not know the precise degree of knowledge which he has 

 attained on the subjects on which he treats, relatively to that 

 which has been attained by others. V/e are sorry to be so 



