QUANTITATIVE ANALYSIS 



such solutions, Longwell and Hill (8) have modified the Rehberg 

 burette by introducing an elastic rubber diaphragm between the 

 mercury and the solution. Clark, Levitan, Gleason, and Greenberg 

 (5) have applied Scholander's micrometer principle, but employ the 

 micrometer screw to push air (instead of mercury) from a hypodermic 

 syringe into a capillary which delivers the solution. 



The general principles of volumetric microanalyses have been 

 clearly elucidated by Conway (6). 



Gasometric Analysis 



One of the oldest quantitative analyses in biochemistry is the 

 determination of urea by measurement of the nitrogen gas liberated by 

 reaction with alkaline bromine solution. It exemplifies procedures in 

 which a substance is measured by the amount of gas that it liberates 

 when it reacts with properly chosen reagents. In such analyses, the 

 measurement is based, as in gravimetric methods, on direct observation 

 of the amount of substance obtained, independent of comparison with 

 standard solutions, such as are required in titration and colorimetry. 

 Combined with this independence are the advantages of a quick meas- 

 urement and easy adaptation to micro quantities. Historically, micro 

 gasometric procedures were introduced into biochemistry for deter- 

 mination of the blood gases, and were then adapted to more general 

 analyses. 



The first of such procedures was the blood gas analysis of Bar- 

 croft and Haldane (12) in which the oxygen liberated from blood by 

 ferricyanide, or the carbon dioxide liberated by acid, was measured 

 by the gas displaced into a capillary tube. The procedure requires 

 accurate temperature control and constant shaking until equilibrium 

 between dissolved and supernatant gases is reached. The method was 

 elaborated by Warburg (19), and has been used for a great variety of 

 purposes by Warburg and others, particularly in following the course 

 of enzymic reactions by measurement of the oxygen absorbed or the 

 carbon dioxide evolved. The ease with which the course of a reaction 

 can be followed by observing the increase in gas volume particularly 

 adapts the procedure to the observation of comparative reaction veloci- 

 ties (13). A recent refinement of the apparatus, and the principles 

 of its use, are described by Summerson (15). 



Ill 



