n8 A CHEMICAL SIGN OF LIFE 



the mercury in the little vessel can be sucked up to the 

 mark, thus making the remaining volume of the left 

 chamber exactly 15 c.c. 1 With a pipette fill the mercury 

 burette T with mercury to the mark, open stopcock G 

 90 to the right, open stopcock C' very gently till 

 mercury falls to the second mark in burette T, which is 

 so marked that by introducing this amount of mercury 

 the remaining volume in this chamber B is now 15 c.c. 

 after the barium hydroxide is introduced to the top of 

 the barium hydroxide tube in left chamber A . (There- 

 fore, by introducing mercury to this mark, chamber 

 B has a capacity less than 15 c.c., but by introducing 

 barium hydroxide in the left chamber A , some of the 

 mercury will be pushed back, so that the capacity of the 

 right chamber B is now finally exactly 15 c.c.) Now 

 shut stopcock C' (very important). With a pipette add 

 mercury to the mercury burette till the level of mercury 

 in it becomes a little lower than that of the mercury in 

 chamber B. Now pull out the core of stopcock /, so as 



1 The exact volume of each chamber should be calibrated once for 

 all. If this is done, one can always work with a constant volume in 

 both chambers, so that when a known amount in cubic centimeters of 

 mercury is introduced so as to bring it up to the marks in the chambers 

 the remaining volume will always be the same. The advantage in 

 having both chambers equal in capacity is obvious. One of our appa- 

 ratuses has a capacity of 21 . 5 c.c. in chamber A and 22 c.c. in chamber B. 

 We therefore introduced 6.5 c.c. into A and marked the level of the 

 mercury, and 7 c.c. into B and did likewise. Thus when mercury is 

 introduced up to the marks, both chambers have the same remaining 

 volume, namely, exactly 15 c.c. A little error in calibrating the chamber 

 A is not very serious, as this chamber is used for the analytic purpose 

 only, while the biometer is to be used as a quantitative apparatus; but 

 the chamber B must be calibrated with extreme care, and each intro- 

 duction of the known amount of the mercury must be done accurately. 

 This can be accomplished by means of the mercury burette T, which is 

 well calibrated and can measure off any known amount of mercury with 

 a high degree of accuracy. 



