38 
HOT-WATER APPARATUS. 
cinders, the power is greatly increased; but cinders are the best fuel for these 
furiiaces, and they will not burn coal. 
Fig-. 2. The circular damper c c should be nearly as large as the upper 
diameter of the furnace, and suspended from the lid' about 4 inches below the top. 
The inverted cone should extend to within about one half of this circular damper, 
and its opening be rather less than that circle. The small damper in the chimney 
regulates the draft. 
With respect to the reservoir, for stove heat it should contain four or five times 
as much as the pipes, nay, if not inconvenient, six or more would be better ; as 
here the object is to maintain constant heat, and such a reservoir once heated would 
hardly grow cold in twenty-four hours, and is heated again very fast, so that three 
or four hours' fire in twenty-four would be sufficient. For greenhouse work, a 
smaller reservoir, holding two or three times the contents of the pipes, would be 
large enough, and of course the smaller the reservoir the shorter time it takes 
to get the apparatus up to full power. It is, however, found in the case of 
No. 1, that a reservoir containing nearly six times as much as the pipes is not 
inconveniently large ; and such reservoirs have this advantage, that they obviate 
all danger of boiling the water to waste. 
In conclusion, it may be well to repeat that the iron pipes should be entirely 
above the boiler (one inch is sufficient height), and that they should incline 
upwards from the point at which they receive hot water from the boiler, to the 
point at which they deliver it to the reservoir. One inch in twenty feet is suffi- 
cient. This arrangement will generally be found most convenient, but where it is 
otherwise, and in all cases where the pipes are of considerable length, say above 
eighty feet, it is advisable to place the air-pipe at the end farthest from the boiler^ 
and give both pipes an equal inclination to the boiler and reservoir. 
To those who are turning their attention to this subject, an excellent paper 
in the Hort. Trans. Lond., by Mr. C. Stodart of Bath, afi'ords much valuable 
information ; though he does not give us the ratio between areas of pipe, and 
areas of glass, requisite to produce certain temperature ; probably because the 
defects of imperfect glazing would render such ratios practically almost useless : 
nevertheless a knowledge of them would not be without use, and to those who have 
leisure and ability for the work, the experiments of Messrs. Dulong and Petit, and 
other tables published in the Encyclopaedia Metropolitan a, under the article " Heat," 
afford ample data. 
From a few rough experiments, it would appear that one square foot of pipe 
to seven of glass for greenhouse temperature^ and one square foot of pipe to three 
and a half of glass for hothouse, are nearly the true proportions. 
Since writing the above, we have had an opportunity of consulting Tredgold 
on Warming and Ventilation, a work in which the subject is treated in a manner at 
once so scientific and so practical, as to leave little, if any thing, to be desired. It 
is indeed a master-piece of practical science, and ought not only to be in the hands, 
but in the heads, of every one who undertakes to apply water to the purposes of 
heating. We would hardly presume to offer any criticisms upon it, but in one 
