200 



SURFACES AND MEMBRANES 



minus one tenth of a calibrated division will introduce an error of not 

 more than 9.15 mm of mercury in the osmotic-pressure observations. 



TABLE V-8 

 Physiological Fluids 

 Data show mean per cent water content. 



* W. S. Duke-Elder, Physiol. Rev., 14, 483 (1934). 



In physiological or medical investigations, if the quantities of fluids 

 available are not too small, a thermocouple or Beckmann thermometer 

 having a range of 3° C with intervals calibrated in hundredths of a degree 

 can be used. If only small quantities of fluid are available, a micro- 

 Beckmann thermometer can be used. The micro-Beckmann thermome- 

 ter has an overall length of 28 cm with a linear spread of 3.5 cm per 

 degree. Since each tenth degree is calibrated into 10 divisions, it is 

 possible, with the aid of a reading glass, to obtain a reliable freezing- 

 point reading to 0.002° C. 



The freezing-point apparatus as assembled is shown in Fig. V-8. The 

 Beckmann thermometer B and stirrer C are inserted into the freezing- 



TABLE V-9 



Freezing Mixtures 



Proportion of substance I to be added to proportion of substance II to produce a 

 freezing mixture having temperature t° C 



Substance 



1 



II 



fC 



Courtesy Chemical Rubber Publishing Company, Cleveland, Ohio. 



