d with
water-vapor at the room temperature. To remove this water-vapor the air
is passed through a tower filled with pumice-stone drenched with
sulphuric acid. It leaves the tower through the tube C and enters the
ventilating air-pipe on its way to the calorimeter.

The method of manipulation is very simple. After connecting the U-tubes
the pet-cock connecting the tube C with the pipe is opened, the mercury
reservoir E is lowered, and air is allowed to pass through until the
meter registers 10 liters. By raising the reservoir E the air supply is
shut off, and after closing the stop-cock at C the tubes are
disconnected, a second set is put in place, and the operation repeated.
The U-tubes are of a size having a total length of the glass portion
equal to 270 millimeters and an internal diameter of 16 millimeters.
They permit the passage of 3 liters of air per minute through them
without a noticeable escape of water-vapor or carbon dioxide. The
U-tubes filled with pumice-stone and sulphuric acid weigh 90 grams. They
are always weighed on the balance with a counterpoise, but no attempt is
made to weigh them closer than to 0.5 milligram.

GAS-METER.

The gas-meter is made by the Dansk Maalerfabrik in Copenhagen, and is of
the type used by Bohr in many of his investigations. It has the
advantage of showing the water-level, and the volume may be read
directly. The dial is graduated so as to be read within 50 cubic
centimeters.

The Elster meter formerly used for this purpose was much smaller than
the meter of the Dansk Maalerfabrik we are now using. The volume of
water was much smaller and consequently the temperature fluctuations
much more rapid. While the residual analyses for which the meter is used
are of value in interpolating the results for the long experiments, and
consequently errors in the meter would be more or less constant,
affecting all results alike, we have nevertheless carefully calibrated
the meter by means of the method of admitting oxygen from a weighed
cylinder.[23] The test showed that the meter measured 1.4 per cent too
much, and consequently this correction must be applied to all
measurements made with it.

CALCULATION OF RESULTS.

With an apparatus as elaborate as is the respiration calorimeter and its
accessories, the calculation of results presents many difficulties, but
the experience of the past few years has enabled us to lessen materially
the intricacies of the calculations formerly t