506 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



The levels of the manometer on each side are read. The levels are 

 again read after i minute ; they should be the same as before and almost 

 identical, e.g. at 9*5 on each side. A difference of '05 between them may 

 be neglected. If they are not identical, both taps are opened to the air 

 and closed again, and this is continued until they are identical, i.e. till the 

 temperature is constant. 



The apparatus is removed from the bath (taps shut to the air, open to 

 manometer) and the permanganate and water upset into the flask by shaking. 



The flasks are shaken for i minute. The apparatus is replaced in the 

 bath for 5 minutes. 



The levels of the manometer are read and they are read again after 

 successive minutes till they remain constant. 



The liquid in the permanganate bottle should be pink. 



The difference of level of each side is calculated by subtraction, e.g. 9-5 

 has decreased to 7*55 and 9*55 has increased to 11*50, i.e. 1-95 and 1*95. 

 The total difference is thus 3*9 cm. or 39 mm. 



As the temperature has been constant, the pressure (p) varies as the 

 volume (v) 



i.e. v = K/> or K = - 

 / 

 p is 39 and v is '1887 c.c. at o and 760 mm. 



or -1887 x 







273 



where / and B are the temperature and barometric pressure at the time 

 of the experiment. K is then calculated. This is the constant where the 

 bottle contains 3-2 c.c. ; hence the constant for the empty bottle is (K - -32). 



FIG. 71. (From J. Physiol., 47, 273, Cambridge University Press.) 



The constant is more easily determined by Hoffmann's procedure, 

 Fig. 71 shows the apparatus required: 



