388 



APPENDIX. 



TORSION BALANCE. 



This instrument is of value for the rapid weighing of small amounts of 

 substances, such as blood taken from a finger-prick, etc. 



The instrument is used as follows for the weighing of blood on a piece of 

 absorbing paper, as for the micro-analysis of sugar (see p. 254). 



Fig- 55 



Remove the clip G and paper from the arm D. Move C until the indicator 

 A is at zero on the scale. See that the lever E is in such a position that F 

 points to " Free." The movable arm B should now be at O. If this is not 

 so, bring B to O by means of an adjusting screw on the back of the instrument. 



Now set F to " Stop " by means of E. Hang the clip and paper on to D, 

 seeing that the paper hangs freely. By means of C move the lever A to mark 

 about 120 mgm., set F to " Free," and then move C until B is at O. The 

 reading at A is the weight of the paper and the clip. After the blood has been 

 drawn on to the paper, the weight is again taken as before. This should be 

 done as rapidly as possible to avoid errors due to evaporation. 



The paper and clip should never be put on or taken off D with F at 

 " Free." The indicator should be set at the approximate weight before the 

 spring is released. By taking these precautions the instrument will remain 

 reliable for a very long time. 



