nation of carbon dioxide and
oxygen on the Pettersson principle has been devised by Sonden and
constructed for us by Grave, of Stockholm.

In the control experiments, the air leaving the mercury valve D (fig.
30, page 66) was caused to pass through a T-tube, one arm of which
connected directly with the sampling pipette of the Sonden gas-analysis
apparatus, the other arm connecting with the U-tubes for residual
analyses. By lowering and raising the mercury reservoir on the
gas-analysis apparatus, a sample of air could be drawn into the
apparatus for analysis. The results of the analysis were expressed on
the basis of moist air in volume per cents rather than by weight, as is
done with the soda-lime method. Hence in comparison it was necessary to
convert the weights to volume, and during this process the errors due to
not correcting for temperature and barometer are made manifest. However,
the important point to be noted is that whatever fluctuations in
composition of the residual air were noted by the soda-lime method,
similar fluctuations of a corresponding size were recorded by the
volumetric analysis with the Sonden apparatus. Under these conditions,
therefore, we believe that the gravimetric method outlined above is
sufficiently satisfactory, so far as the carbon-dioxide content is
concerned, for ordinary work where there are no wide variations in the
composition of the air from period to period.

NITROGEN ADMITTED WITH THE OXYGEN.

It is impossible to obtain in the market absolutely chemically pure
oxygen. All the oxygen that we have thus far been able to purchase
contains nitrogen and, in some instances, measurable amounts of
water-vapor and carbon dioxide. The better grade of oxygen, that
prepared from liquid air, is practically free from carbon dioxide and
water-vapor, but it still contains nitrogen, and hence with every liter
of oxygen admitted there is a slight amount of nitrogen added. This
amount can readily be found from the gasometric analysis of the oxygen
and from the well-known relation between the weight and the volume of
nitrogen the weight can be accurately found. This addition of nitrogen
played a very important role in the calculation of the oxygen
consumption as formerly employed. As is seen later, a much abbreviated
form of calculation is now in use in which the nitrogen admitted with
the oxygen does not influence the calculation of the residual oxygen.

REJECTION OF AIR.

In long-contin