AND ITS BEARINGS ON PATHOLOGY. 355 
The door can be screwed by means of nuts (G, Fig. 3) against the edge 
of the box (represented by dotted lines in the sketch) ; and the cotton-wool, 
having the narrow rim of metal thus firmly pressed against it, serves as an 
effectual filter of the air that passes in during cooling. But then it is essential 
that the heat be so equably distributed as to avoid heating any portion of the 
cotton to such a degree as to destroy its physical properties. The cotton-wool 
which you now see in the 
lid has been used for several i Me 
experiments ; yet you ob- 
serve it is only slightly 
browned ; it is not singed 
at any part, as it would 
have been unless the heat 
had been nearly uniform. 
This uniformity of the heat 
is provided for by having 
three shelves of sheet-iron 
(H H H) interposed between 
the large Bunsen’s burner 
(I) and the bottom of the 
box, so as to prevent the 
heat from acting directly 
upon it; while at the same 
time the box is covered 
over with a cover of sheet- 
iron (KK), which reaches 
nearly to the ground, and, 
while it checks radiation, 
compels the heated air to 
travel over the whole ex- 
terior of the box and escape by holes at the top of the cover, whence it is 
conducted into a chimney by the tube (L). By these two means combined, the 
shelves below and the cover round about, we get the result which you see here. 
The cotton at the top of the box is browned to just the same degree as that 
at the bottom. Into such a box (about one foot in its three dimensions and 
furnished with a shelf in the middle) we may put a dozen sets of covered glasses 
such as I have described, together with their glass plates and shades. An aperture 
in the top of the box, well packed with cotton-wool, transmits the thermometer 
(M) to show when the temperature of 300° has been attained ; and when this 
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