688 KANSAS CIl Y REVIEW OF SCIENCE. 
practicability of maintaining a sufficient and equable temperature, and a whole- 
some atmosphere in a room warmed by a stove, is far from being realized; still 
less, the convenience of warming several rooms at the same time by the same 
means, hot-air furnaces scarcely being known. 
The essentials for healthy stove-heat are a brick-lined fire-chamber, exhaust- 
flue for foul air, means for supplying moisture, and provision for fresh-air sup- 
ply. A brick lining is requisite for the double purpose of preventing overheat- 
ing, and for retaining heat in the stove. For the supply of moisture, the means 
are simple and easy of control, but often inadequate. An efficient foul-air shaft 
may be fitted to the commonest of close stoves by simply inclosing the smoke- 
pipe in a jacket — that is, in a pipe of two or three inches greater diameter. 
This should be braced round the smoke-pipe and left open at the end next the 
stove. At its entry into the chimney, or in its passage through the roof of a car, 
as the case may be, a perforated collar should separate it from the smoke-pipe. 
For stoves with a short horizontal smoke-pipe, passing through a fire-board, the 
latter should always be raised about three inches from the floor. A smoke-pipe 
thus jacketed, or fire-board so raised at the bottom, affords ample provision for 
the escape of foul air. 
The introduction of fresh air is a comparatively easy matter, when by no more 
special provision, then by a strip of board under the window-sash, closely fitted. 
The lap of the sash at the middle admits the air with a direction to the ceiling, 
and, consequently, without draft on any one in the room. 
The experiments of Pettenkofifer have shown that under the common con- 
ditions of the atmosphere, a very considerable exchange of gases takes place 
through dry plastered walls, brick, and stone. And it is the common exper- 
ience of sick persons that they are sensitive to drafts through walls when the 
wind blows, and that they frequently take cold by exposure to the windy side of 
the house. 
All flues for the exit of foul air should be perfectly smooth and tight. 
Rough surfaces not only retard but retain emanations which come in contact 
with them. Moreover, exhaust-flues should never be placed in outer cold walls, 
because the geatest density of the outer cold air prevents the ready ascent of the 
warmed and rarefied air from within. Another important consideration is 
the size of air-shafts. This can only be approximate, however, because the 
amount of air which will pass through a shaft depends in a great degree upon 
the relative temperatures of the inner and outer atmospheres, and the conditions 
of the weather, particularly the direction of the wind. As a practical average, 
the best observers recommend that the sectional area of both inlet and outlet 
shafts be twenty-four square inches per head ; or, for buildings of three stories, 
one square inch for every fifty cubic feet of space ; rooms below, one square inch 
for every fifty-five cubic feet ; for ground floors, one square inch for every sixty 
cubic feet. It should be borne in mind that the friction in long flues consider- 
ably lessens the extractive power, and that the column of air in the flue increases 
in density as it ascends. In prisons, where the cubic space per head is compar- 
