74 MUSCULAR WORK 
of a high grade, namely, of about 98 per cent purity, and measure the volume 
of gas passing through the Bohr gas-meter, assuming that no air escapes 
from the system through the mouth or nose of the subject, or through defec- 
tive connections. Since every liter of air leaking out of the system through 
the mouth, the nose, or defective connections must be replaced by a liter of 
oxygen in order to bring the air again to the normal volume, such loss of air 
affects only the oxygen determination. 
To provide against any such loss of air through defects in the absorbing 
system the apparatus was tested every morning by running the motor for 
several minutes before connecting the subject with it, the volume of air in the 
system being carefully noted at the beginning and end of the test. If a leak 
was found no experiments were made until the apparatus was proved to be 
tight. Practically the only other source of leaks possible, therefore, was about 
the nose and mouth of the subject. Since there was especial danger of such 
leaks in the muscular-work experiments, the utmost precautions were taken 
to prevent them. The nose of the subject was closed with a clip supplied 
by Siebe, Gorman & Co.; as a further check upon the complete closure of 
the nose and mouth, it was an invariable rule to cover the face around the 
noseclip and mouthpiece with soapsuds so that the slightest leakage of air 
through the nose or the mouth would be instantly indicated by bubbles. 
In determining the oxygen consumed by the subject, all of the values 
are referred to the same basis, namely, the weight of a liter of the gas issuing 
from the cylinder when the valve is open. This is true irrespective of whether 
the determination is made by noting the loss in weight of a cylinder of the 
highly compressed gas or by using the Bohr gas-meter immersed in water, 
since the method of calibrating the gas-meter involves the use of the weighed 
cylinder of oxygen. In a recent description of the method of calibration and 
of computing the oxygen consumption, attention was called to the fact that 
but rarely is pure oxygen available, the residual gas unabsorbed by potassium 
pyrogallate being usually about 3 per cent." This residual gas has commonly 
been considered as nitrogen, and the difference in weight per liter of the oxygen 
and nitrogen has been taken into consideration in the computations. 
Recently an interesting paper has appeared by Morey, 6 who examined 
the impurities in the commercial oxygen made from liquid air. Inasmuch 
as practically all of the oxygen used in this laboratory is obtained from the 
Linde Air Products Company and is derived from liquid air, the interesting 
observations of Morey hold true with the use of this gas. Morey finds that 
the residual gas is not wholly nitrogen, but is in large part argon, a sample 
of oxygen analyzed by him showing 96.9 per cent of oxygen, 2.8 per cent of 
argon, and 0.3 per cent of nitrogen. He points out that this confirms the work 
of Claude," who has noted that argon to the extent of about 3 per cent is 
the chief impurity in oxygen prepared by the Claude process. 
After the manuscript and computations for this report were practically 
completed, our attention was called by Mr. H. L. Higgins of the laboratory 
staff to the possible influence on our results of the presence in the oxygen of 
argon. Mr. Higgins maintained correctly that if gas were used containing 
97 per cent oxygen and 3 per cent nitrogen, the weight of a liter would be 
o Benedict, Deutsch. Archiv f. klin. Med., 1912, 107, p. 181. 
6 Morey, Journ. Am. Chem. Soc, 1912, 34, p. 491. « Claude, Comptes rendus, 1909, 181, p. 752. 
