1905.| On the Physiological Processes of Green Leaves. 33 
metres of the bottom of the glass vessel, is closed with a silver plate pierced 
with fine holes about 0°5 mm. in diameter. There should be not less than 
ten of these holes per square centimetre. 
Two other similar perforated plates are fixed in the vertical tube at heights 
of about 12 and 25 cm. respectively, and the upper part of the tube 
is closed with a perforated india-rubber plug, through which passes a tube 
connecting with the meter. The side-tubulure of the glass vessel is connected 
either with the leaf-case A or with the outer air as may be required, the 
liquid for absorbing the carbon dioxide being placed in the glass vessel. 
When the water-pump is in action the absorbent liquid rises in the vertical 
tube to a height of about 30 cm., after which air is drawn through the lowest 
perforated plate and rises through the column of liquid in a rapid stream of . 
small bubbles which are broken up and re-formed at each of the two 
succeeding plates, thus producing a very effective “ scrubbing” action. 
The absorption-tubes we have employed are of two sizes, one of them 
having a diameter of 40 mm. (shown at D of fig. 1) and applicable to rates 
of flow of from 200 to 400 litres per hour, and another smaller apparatus 
(shown at E of fig. 1) with a tube diameter of 20 mm. and suitable for 
volumes of air of from 100 to 150 litres per hour. 
This last mentioned apparatus we have had made with glass connections 
throughout. In this form it is well adapted for the determination of carbon 
dioxide in the air, and it has the advantage that the whole of the liquid can 
be used for the final titration instead of an aliquot part as in the case of the 
larger apparatus. 
The apparatus as figured is arranged for the determination of the carbon 
dioxide of the air, for which the smaller Reiset’s apparatus E is used, whilst 
the larger Reiset D is connected with the current of air coming from the 
experimental leaf-case. The water-pump is not shown in the illustration. 
Instead of baryta, as originally employed by Reiset, we use a 4-per-cent.- 
solution of pure caustic soda (made from sodium) as the absorbent. 
After displacing the air in the absorption-apparatus with air freed from 
carbon dioxide* a definite volume of the soda-solution is run into the 
“ Reiset ” through the side opening of the large vessel, every precaution being 
taken to avoid absorption of atmospheric carbon dioxide during the process. 
~The larger apparatus requires 400 c.c. and the smaller 100 c.c. of the solution. 
This apparatus acts as a most efficient absorber of the carbon dioxide of 
ordinary air, and of air artificially enriched with that gas up to ten or 
* The Winkler apparatus is used for this purpose, the air being driven through it with an 
ordinary india-rubber ball-pump. 
VOL, LXXVI.—B. D 
