236 PHOTOSYNTHESIS 



mine the volume of the gas Hberated in unit time and to determine the 

 oxygen content of this. Also it is important to observe the increase 

 of oxygen in the water. Finally it must be realized that the tempera- 

 ture of the v^ater surrounding the plants must remain constant, for a varia- 

 tion of 0.2° afifects the size of the bubble very appreciably. 



Bose ^^ has devised an apparatus in which the bubbles escaping from 

 the cut end of the plant are collected under an oil valve. When the 

 pressure of the gas attains a certain pressure, it lifts the oil valve and 

 escapes. The apparatus is devised so that successive escapes from the 

 valve represent equal volumes of gas which are independent of the fre- 

 quency and the size of the bubbles which are emitted from the plant. 

 With this apparatus Bose has also constructed an electrical device which 

 records by a dot on the drum of a clock each time the gas passes the 

 valve. By means of this apparatus the rate of photosynthesis is recorded 

 directly on the drum by the frequency of the dots in a period of time. 

 Undoubtedly this ingenious piece of apparatus can serve to demonstrate 

 approximately the rate of photosynthesis under different conditions. It 

 has, however, the same objection as the original method — namely, that 

 it does not measure the amount of oxygen which is emitted, but only 

 the total gas, and, as has been pointed out, the composition of this gas 

 is not constant, but the amount of oxygen contained therein varies with 

 the rate of photosynthesis. 



f. Gas Analytical Methods. 



Oxygen Absorbents. The methods of gas analysis for general chem- 

 ical analytical work have been rei:)eatedly discussed and compiled and sev- 

 eral excellent treatises have been prepared. ^^ While, of course, the gen- 

 eral principles are the same for biological work and especially for in- 

 vestigations in plant respiration and photosynthesis, little has been done 

 to collect the required information. In applying these general methods 

 it has been found that biological work requires many alterations both as 

 to procedure and accuracy demanded. For this reason biological gas 

 analysis is to be regarded as a special and advanced chapter of chemical 

 analysis and sets as a prerequisite a thorough understanding of the 

 fundamental chemical principles involved. This includes the precautions 

 and treatment of glass ware, stop-cocks, mercury, rubber, the calibra- 

 tion of apparatus, the taking and handling of gas samples, reading of 

 burettes, etc., as well as, of course, the fundamental gas laws. 



The composition of the atmosphere and esi^ecially its oxygen-content 

 has been a subject of keen interest for a very long time. In fact, as 

 has been stated, Ingen-Housz, the discoverer of photosynthesis, was pri- 



"Bose, "The Physiology of Photosynthesis," Longmans, Green & Co., 1924, p. 17. 



" Hempel, W., translated by G. L. M. Dennis, "Methods of Gas Analysis," The 

 Macmillan Company. Foster, C, Le Neve and Haldane, J. S., "The Investigation 

 of Mine Air," Charles Griffin & Co., London. Haldane, J. S., "Methods of Air- 

 Analysis," London, 1912. Geppert, L, "Die Gasanalyse und ihre physiologische 

 Anwendung," Berlin. 



