APPENDIX 
THE BIOMETER: HOW TO USE IT 
The study of carbon dioxide has been so connected 
with various forms of human activity that in spite of 
natural difficulties methods for its accurate quantitative 
determination have been highly developed. Never- 
theless, none of the various methods of analysis can be 
used for very minute quantities of carbon dioxide. The 
greatest difficulty in using any micro-gas analysis is in 
securing freedom from the external variations of tempera- 
ture and pressure. Particularly is this so in the case of 
carbon dioxide, for we need to consider, not only the 
effect of temperature and pressure variation, but also 
how to free the apparatus from atmospheric carbon 
dioxide. After we discovered a new method which 
detected exceedingly minute quantities of this gas we 
found that the ordinary method of freeing air or any 
other gases from carbon dioxide was not sufficiently 
accurate, although it should be admitted that our 
experience in washing gases was not very extensive. 
The biometer is constructed with a view to meeting 
these difficulties and has shown itself to be remarkably 
convenient for many biological as well as chemical 
investigations. 
Uses of biometer—The biometer can detect carbon 
dioxide in as small quantities.as one ten-millionth of a 
gram. This is the amount contained in one-sixth of a 
cubic centimeter of the purest air, in which we assume 
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