PHENOMENA OP WINTER. 
11 
a given heat. If charcoal be the type, although that substance cannot, in general, 
be employed, yet clear burning coke may ; and must be used in the cylindrical boiler. 
From these data, though it cannot be expected by any one of us, that the great power 
of heat above mentioned, will ever be developed by even the best acting furnaces 
which we as yet possess, a comparative approximation can be attained ; or the 
defect of heat may be so apparent as to prove the value of the one, or the worthless- 
ness of the other. Suppose, for instance, that 50 or 52 lbs. of coke heat 600 gallons 
of water to a very efficient forcing power, while in another apparatus the heat 
developed by the same fuel is very much lower. In these cases, although it can 
never be presumed that the better of the two boilers will command the entire heat 
which the combustible can develope, yet it will be evident that the more defective 
boiler being the cause of a daily and injurious loss, demands the substitution of 
one differently constructed ; or, at least, that the present be differently placed. We 
have never as yet seen a more powerful furnace than the one described in a former 
number under the term " Saddle-boiler." 
Dr. Miller proceeds—" Some waste is almost inevitable," and " the first and 
most obvious loss, arises from the escape of the heated air from the chimney, before 
it has surrendered to the boiler the full amount of heat which it is capable to 
relinquish. It is manifest that the best method of obviating this, consists in so 
arranging the chimney and passages for the products of combustion, that they shall 
circulate thoroughly around the boiler, and that sufficient time may be allowed for 
them to part with their high temperature before escaping into the open air." These 
are plain facts, which have been often noticed, but found difficult to accomplish. 
However, the cylinder boilers, wherein the fire is confined to the inner case, is 
evidently defective, because the flame does not touch the external surface, but passes 
off over the upper rim of the boiler at once into the flue ; as a remedy, the flue 
should be continued within the house, so as to confine and radiate all the heat possible. 
Other boilers, wherein the entire centre contains the fire, and which force all 
the flame to pass over the top, and around the outer sides of the plates, must be 
vastly more efficient ; but still there remain defects, and one of these, of very con- 
siderable moment, is thus noticed in the lecture. The knowledge of this, and the 
remedy for it, " is intimately connected with the chemistry of combustion. It de- 
pends upon an insufficient supply of air. It is a fact not less singular than im- 
portant, that charcoal or coke may be dissipated in vapour, and may apparently be 
wholly consumed, by one half of the amount of air that is usually required in an open 
fire, under circumstances where the full quantity of heat is given out. This 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 quantity or amount of oxygen 
is taken up, and carbonic acid or ' fixed air ' is produced : in the second case, a gas 
is also obtained, called carbonic oxide; it is colourless, and therefore escapes 
notice ; but it is combustible, which carbonic acid is not, and in burning it gives a 
large amount of heat — in short, the other four-fifths of the heat, which are deficient 
