THE BIOMETER: HOW TO USE IT 115 



closely. The best way to set it up is to mount it per- 

 manently, instead of clamping it with several iron 

 clamps and stands. The apparatus set up as in Fig. i 

 in the lead frame or in the wooden frame not only looks 

 better, but is subject to less damage. 



How to clean the apparatus. The apparatus is con- 

 structed and is mounted in such a way that washing and 

 cleaning can be done after each experiment without 

 taking it apart. Although the procedure of washing 

 is exceedingly simple, it is better for the beginner to 

 follow exactly the directions given below, for there are 

 many stopcocks which have to be turned in a particular 

 direction in order to avoid unnecessary accidents which 

 sometimes necessitate the expenditure of considerable 

 time in bringing the apparatus back into a working con- 

 dition. An example will illustrate this: If one forgets 

 to turn the stopcock L during the washing, and the 

 space between L and K becomes wet, it will require 

 about five or six hours to wash the space and clean and 

 dry it. The old saying that an ounce of prevention is 

 worth a pound of cure should be borne in mind here. 



Turn the water pump on. Now turn stopcock E 

 1 80 to the right, so that the barium hydroxide solution 

 is entirely out of connection with the other two arms of 

 the stopcock E. Remove mercury from stoppers S and 

 R with a pipette, and then remove the stoppers S and R, 

 and tissues if there are any. Turn stopcock L in such a 

 way that the bore inside will look like this JL, thus 

 severing the connection between the vertical arm of L 

 and the horizontal arms. Turn on stopcocks J and 

 Q and F in order. Turn stopcock G 90 to the left. 

 Withdraw the mercury from chamber A by opening 



