Sec. 8.3] INDIRECT METHODS FOR MEASURING DEUTERIUM 



267 



The difference in density goes through a maximum at about 40°C. The 

 precision of temperature control required will be mentioned in the discussions 

 of the individual methods. The techniques for thermoregulation are dis- 

 cussed under the falling-drop method. 



Table 31. Densities of Natural Water and DoO 



A pressure increase of 1 atm increases the density of water by about 

 0.005 per cent. Organic liquids are affected by about the same order of 

 magnitude. It is apparent, therefore, that the ordinary daily fluctuations of 

 pressure (about 2 ^760 atm) are negligible in almost all density determinations. 



Dissolved air also decreases the density of water. Various workers do not 

 agree on the extent of this effect, but at 20°C the difference in density between 

 air-free water and water that has been in contact with air for 3 or 4 days is 

 about 2 X 10- 6 to 2 X 10~ 7 [37]. 



8.3. Preparation and Purification of Water Samples for Analysis. Organic 

 compounds are analyzed for deuterium content by burning them to form 

 water, collecting and purifying the water formed, and determining the 

 deuterium oxide content of this water [13,14]. Combustion is carried ouc 

 in a quartz or Vycor tube packed with cupric oxide and heated to 750°C. 

 Oxygen manufactured from liquid air is bubbled through sulfuric acid and 



