428 Baker . — Quantitative Experiments on 
to those represented by the chemical formula for the complete oxidation of 
a glucose : — 
C 6 H 12 0 6 + 60 2 = 6C0 2 + 6H 2 0. 
As there is no reason to believe that there is a definite or general 
chemical process always concerned in the complex oxidation reactions 
included under respiration, it was essential to determine these weight 
relations for mustard seeds germinating under the experimental conditions. 
For this purpose, several modifications of the original apparatus were 
necessary, and finally a somewhat complicated apparatus was used. 
General Experimental Methods. 
The apparatus used was similar to that shown diagrammatically in 
Text-fig. 4, except that the paraform tubes and the absorption apparatus for 
formaldehyde were omitted. The aim of the experiments was to find the 
loss in weight of the cultures, and also the total weight of carbon dioxide 
and water evolved during growth. The seeds, which had been desiccated 
over calcium chloride, were grown, as in the former experiments, on tared 
Petri dishes filled with dry sand. A separate experiment with three 
weighed amounts of the same seed, heated to 8o°-ioo°, gave the loss in 
weight on heating and hence the true dry weight of the seeds. A second 
experiment gave the total gain in weight of the seeds on hydrolysis, by 
hydrolysing them with dilute acid. When first set, the seeds were moistened 
with a weighed amount of pure distilled water, and their later requirements 
were supplied by means of nutrient solution from an automatic waterer (as 
described on p. 415) of suitable size. The waterer could also be accurately 
weighed, before and after the experiment, which gives the amount of 
nutrient solution given to the culture. The seeds, supported on the base 
of the waterer, were contained in a ‘ vacuum ’ desiccator, with two glass 
tubes sealed through its glass stopper, through which a continual current of 
air was passed over them. Light was carefully excluded from the desiccator 
with a black cloth shade. The air-current was produced by pressure from 
a water-jet pump (as described on p. 417), freed from C0 2 (as in the former 
experiments) by means of soda lime and strong caustic potash, and dried 
by calcium chloride. 
After from seven to fourteen days the plants had grown to the height 
of from 3 to 7 cm. They were then weighed, first wet and then dry. The 
drying was effected by heating to 8o°-ioo° for some hours, and cooling in 
a calcium chloride desiccator. 
The Absorption of Carbon Dioxide. 
This was effected by means of a Liebig’s absorption bulb, filled with 
very concentrated potash solution and with a calcium chloride tube sealed 
on to it to prevent loss of water from the bulb ; the air-current was passed 
