rests are
extended so as to provide for supports for the outer walls of asbestos
wood, which serve to insulate the calorimeter. Between the channels
beneath the calorimeter floor and the 3-inch channels is placed a sheet
of zinc which forms the outer bottom metallic wall of the chamber.

In order to prevent conduction of heat through the structural steel all
contact between the inner copper wall and the steel is avoided by having
strips of asbestos lumber placed between the steel and copper. These are
shown as J in fig. 8 and fig. 12. A sheet of asbestos lumber beneath the
copper bottom likewise serves this purpose and also serves to give a
solid foundation for the floor. The supporting channels are placed near
enough together to reinforce fully the sheet of asbestos lumber and
enable it to support solidly the weight of the man. The extra strain on
the floor due to tilting back a chair and thus throwing all the weight
on two points was taken into consideration in planning the asbestos and
the reinforcement by the steel channels. The whole forms a very
satisfactory flooring.

_Wall construction and insulation._--The inner wall of the chamber
consists of copper, preferably tinned on both sides, thus aiding in
soldering, and the tinned inner surface makes the chamber somewhat
lighter. Extra large sheets are obtained from the mill, thus reducing to
a minimum the number of seams for soldering, and seams are made tight
only with difficulty. The copper is of standard gage, the so-called
14-ounce copper, weighing 1.1 pounds per square foot or 5.5 kilograms
per square meter. It has a thickness of 0.5 millimeter. The whole
interior of the skeleton frame of the structural steel is lined with
these sheets; fig. 11 shows the copper shell in position.

For the outer metallic wall, zinc, as the less expensive metal, is used.
One sheet of this material perforated with holes for the attachment of
bolts and other appliances is shown in position on the outside of the
wall in fig. 11. The sheet zinc of the floor is obviously put in
position before the channels upon which it rests are laid. The zinc is
obtained in standard size, and is the so-called 9-ounce zinc, or 0.7
pound to the square foot, or 3.5 kilograms to the square meter. The
sheet has a thickness of 0.5 millimeter.

[Illustration: FIG. 12.--Cross-section in detail of walls of
calorimeter, showing zinc and copper walls and asbestos outside (A);
hair-felt lining (B); cross-sec