1906] BRIEFER ARTICLES 211 
of carbon dioxid, is lifted from the water, shaken free from all adhering 
drops, and placed in position on the chamber. To prevent compression, 
and therefore the presence of too great a quantity, of air in the 
chamber when the stopper is pushed into place, tiny holes (visible 
in the figure), matching in stopper and chamber-neck, allow free 
release of such pressure, and the chamber is perfectly sealed by twisting 
the stopper a little. The lower stop-cock is then opened, permitting 
the carbon dioxid of the tube to diffuse into the chamber, a process 
hastened by its gravitational flow. The apparatus now contains obviously 
2° of plant and 100° of gas, of which a known percentage (say 5, 8, or 10) 
is carbon dioxid, and the remainder is air. The instrument is now placed 
in a bright light (not direct sunlight) for three or four hours; then the lower 
stop-cock is closed (as shown in the figure), shutting into the tube a sample 
of the gas of the chamber at the close of the experiment. The analysis of 
this gas can be made at leisure, and is accomplished thus. The stopper and 
tube are removed and placed upright in the pneumatic trough, deeply 
enough to allow the stopper to be taken off without admission of air to the 
tube. The zero mark of the tube is then brought exactly to the water 
surface; the upper stop-cock is cautiously opened, permitting the water 
to rise slowly to the zero mark, when the stop-cock is again closed, 
shutting into the tube exactly ro®° of the gas to be analyzed. First the 
quantity of carbon dioxid in the tube is determined, which is accomplished 
by aid of a reagent tube, of the form shown at the bottom of the figure. This 
tube, of glass, is provided with an extension of soft rubber tubing closed by 
a screw clamp, and it is filled completely to the clamp with a strong solution 
of caustic potash. It is slipped under the water of the pneumatic trough, 
with the clamp closed; the air, if any, is squeezed from the upper part; and 
the rubber is slipped over the lower end of the measuring tube which it grips 
firmly. The whole is then lifted from the water, the clamp is opened, the 
combination is inverted and the liquid is allowed to flow back and forth 
several times from one tube to the other, when it will completely absorb any 
carbon dioxid present. The clamp is then closed, the combination is slipped 
again under water, and the rubber tube is pulled off, when the atmos- 
pheric pressure will instantly force up the water to the exact extent of the 
carbon dioxid absorbed, permitting the amount, and hence the percentage, 
to be read off directly. Next a determination of the percentage of oxygen 
present is made. This is effected by a precisely similar method, using an- 
other reagent tube containing pyrogallate of potash, freshly made up in the 
usual manner. A few inversions of the combination will result in absorp- 
tion of all the oxygen, and the water-level in the tube when the rubber is 
