1910. | On Vegetuble Assimilation and Respiration. 379 
flowing were taken. This liquid can be drawn out by switching the current 
into the other pipette by the three-way tap & and then disconnecting the 
rubber joint at / or 7%. 
Above the analytical bench on a high shelf are set two 30-litre bottles 
containing N/10 standard baryta and N/20 HCl* having burettes in 
connection with them, one to the baryta, and two to the acid for two 
simultaneous analyses. The procedure for estimating the dissolved CQ, is to 
introduce 25 or 50 cc. of the standard baryta into a clean glass cylinder of 
about 500 c.c. capacity and to take this to the apparatus and draw off into 
it the 200 c.c. of COs-solution. The cylinder is brought back and corked up 
in air-tight connection with one of the burettes of N/20 HCl and the excess 
of free baryta titrated by this acid, using phenolphthalein as indicator and 
stirring by means of a current of CO,-free air forced through the lquid. 
The titre of the original 25 or 50 cc. of baryta being known, the COs- 
content of the 200 cc. of the liquid is obtained in equivalents of N/20 HCl, 
and the weight of COz2 in 100 ce. of liquid is calculated. 
g) Method of Securing Uniform Flow of Effuent.—In maintaining the 
regular flow of the current a special difficulty arises from the fact that the 
outflow pipettes are at intervals completely emptied of their liquid for 
analysis. Should the flow be switched back to an empty pipette when it is 
desired to analyse the contents of the other pipette then, of course, there 
would be a sudden rush of the current owing to the whole height of the 
pipette being added to the effective fall which governs the rate of flow. It 
is therefore essential that, when the circulation liquid has been withdrawn 
for analysis, the pipette be filled up with some liquid or other before the 
current can be safely turned back into it without disturbing acceleration of 
rate. 
For this purpose there is a reservoir of liquid X from which either pipette 
can be quickly filled by turning its controlling tap. This liquid is water 
containing about 7 per cent. of alcohol and tinged with methylene blue. 
Its lower specific gravity allows this accessory liquid to float up in the 
pipette on top of the inflowing stream of the proper solution without 
mixing with it. The colour enables one to see that there is a sharp line of 
separation kept between the two liquids and also to follow the rise of the 
accessory liquid and tell when the whole of it has been driven out at the 
top of the pipette, and the contents again consist only of the proper effluent 
from the chamber suitable for making another analysis. 
If the contents of each pipette were withdrawn for analysis as soon as the 
blue liquid was all driven over then none of the actual liquid from the 
* In later years N/5 baryta and N/10 HCl have been employed. 
