THE BIOMETER: HOW TO USE IT III 
clear, but when more than a definite amount of carbon 
dioxide is introduced, a precipitate of carbonate appears, 
which is detectible by means of a lens. 
3. By the use of accurately known quantities of 
carbon dioxide of exceedingly high dilution it was found 
that the minimum amount of carbon dioxide which gives 
a precipitate is 1.0X1077 g. 
4. By determining, therefore, the minimum volume 
of any given sample of the gas necessary to give the 
first visible formation of the precipitate its carbon 
dioxide content can be estimated accurately, since this 
volume must contain just the known detectible amount 
of the gas, which we found to be 1.0X107? g. 
5. By having two chambers side by side the different 
rates of metabolism from two different tissues can be 
estimated by the different speeds of formation of the 
precipitate and extent of the precipitate. 
Description of the apparatus——The biometer shown 
in Figs. 1 and 3 is made of glass. It consists of two 
respiratory chambers connected by a three-way stop- 
cock L, the other arm of which is connected to one arm 
of another three-way stopcock K. (As is shown in 
Fig. 1, for an ordinary experiment we can connect it 
directly to the nitrometer.) Each of the other two 
arms of stopcock K is connected to a nitrometer, W or 
X, which is used for removing the final traces of carbon 
dioxide from the gas with which the chambers are to 
be filled. The nitrometer on the right is connected to a 
carboy F (see Fig. 5, apparatus III), filled with air free 
from carbon dioxide; and the other, on the left, to a simi- 
lar carboy as a reservoir for any other gases that may be 
used as a special medium for different experiments, such 
