260 



HEATING AS APPLIED IN HORTICULTURE. 



of combustion that they shall circulate 

 thoroughly around the boiler, and that 

 sufficient time may be allowed them to 

 part with their high temperature before 

 escaping into the external air." This is 

 mainly occasioned by the admission of 

 too great a supply of air. " There is, 

 however, a very important, but more 

 unsuspected mode in which loss is 

 sustained, and one which is intimately 

 connected with the chemistry of com- 

 bustion. It depends upon an insufficient 

 supply of air. It is a fact, not less 

 singular than important, that charcoal, 

 or coke, may be dissipated in vapour, 

 and may be apparently wholly consumed, 

 by one-half of the amount of air which 

 is usually required in an open fire, under 

 circumstances where the full quantity of 

 heat is given out ; and it is to be observed, 

 that in this case, 1 lb. of charcoal, instead 

 of emitting heat enough to convert 

 13 lb. of water into steam, will only give 

 out one-fifth of the heat, and will there- 

 fore raise little more than 2^ lb. of water 

 into steam. This important fact depends 

 upon the property which charcoal has of 

 forming two compounds with oxygen. 

 In the first case, where the most heat is 

 emitted, twice the amount of oxygen is 

 taken up, and carbonic acid gas, or fixed 

 air, is produced : in the second case, a 

 gas is obtained also, called carbonic 

 oxide; — it is colourless, and therefore 

 escapes notice ; but it is combustible, 

 which carbonic acid is not; and in burn- 

 ing, it gives out a large amount of heat — 

 in short, the other four-fifths of the heat 

 which are deficient when charcoal is 

 burned into this gas. 



" This gas is not formed, in the first 

 instance, by the direct union of the 

 coke or charcoal with the oxygen of 

 the air ; for carbonic acid is the com- 

 pound which is invariably obtained; 

 but when this carbonic acid is made to 

 pass over red-hot coals, it dissolves a 

 portion of the coal, becomes dilated to 

 twice the bulk it occupied, and actually, 

 instead of increasing the heat of the 

 furnace by the quantity of coal with 

 which it thus unites, it most materially 

 diminishes it, and carries it off in sheer 

 waste. Now, let us consider what is 

 actually going on in many of our fur- 

 naces : these are usually open to the air 

 at bottom by the bars of the fire-grate ; 



brisk combustion takes place, and the 

 body of coke above becomes of a bright 

 red heat ; but the air is quickly deprived 

 of its oxygen by the lowest layer of coal, 

 the draught carries up the exhausted air, 

 and with it the carbonic acid that has 

 been formed ; — this gas, as it passes over 

 the intensely ignited coal, dissolves a 

 fresh portion, cools the fire, and ascends 

 the chimney : when it reaches the top 

 of the chimney, it has become too much 

 cooled down to take fire as it comes into 

 the air, and passes off unsuspected, and 

 to waste, actually carrying with it four- 

 fifths of the heat that it ought to give 

 out, if the coal that it takes off had been 

 burned with a due supply of air. I do 

 not mean to say that the whole of the 

 carbonic acid is ever entirely converted 

 into carbonic oxide : the gas is not in 

 contact with the heated coal for a suffi- 

 cient length of time to produce this 

 effect ; but this I do say, that in all 

 furnaces of the common construction, a 

 large loss is sustained in this insidious 

 and unsuspected manner. In the case 

 where coal, and not coke, is employed, 

 still greater loss is sustained; — all the 

 visible smoke is wasted, a good deal of 

 carbonic oxide in addition passes off in 

 the invisible form, and still more coal 

 gas escapes unnoticed ; the coal in the 

 upper part of the furnace becomes coked 

 by the heat of the lower portion, and 

 nearly all that the gas-works obtain by 

 distillation of coal in retorts, here passes 

 unheated into the air. The question, 

 therefore, for the consumption of smoke 

 resolves itself, not merely into a question 

 of public health and convenience — to 

 which too often a deaf ear is turned by 

 those who are deriving profit at the 

 expense of the sufferers — but it is also a 

 question of economy on the widest scale ; 

 it is a question on which common sense 

 and common humanity are alike agreed ; 

 and it is therefore a point which eventu- 

 ally will demand, from self-interest, that 

 attention which mere good feeling would 

 long solicit in vain." — Pharmaceutical 

 Times. 



In reference to combustion and the 

 management of fuel, we find the follow- 

 ing sensible remarks by Mr Rogers, the 

 inventor of the conical boiler with which 

 his name is associated, given by him 

 in a communication to the "Gardeners* 



