n6 A CHEMICAL SIGN OF LIFE 



stopcock C and from B by opening the corresponding 

 stopcock. Fill both chambers A and B with water 

 acidulated with nitric acid (not more than i per cent), 

 having both stopcocks open, then with distilled water five 

 times, then once with alcohol, and once with alcohol-ether. 

 Two funnels placed under these two chambers (see Fig. i) 

 are connected with a sink, to form an outlet for this 

 waste water. The alcohol and alcohol-ether drained out 

 of these chambers should be saved for re-use. Replace 

 the stoppers S and R. Let the machine remain un- 

 touched for drying while the suction pump is going and 

 while the tissue for an experiment is being prepared. 

 Five or ten minutes will be sufficient for complete drying 

 if the water pump is in good order and the alcohol used 

 has not contained too much water. 



It is very important that we should leave the appa- 

 ratus in this condition until we are ready for an experi- 

 ment, and that no stopcock should be touched, for this 

 is the only condition under which all parts of the appara- 

 tus will dry. 



How to obtain air free from carbon dioxide. It is very 

 difficult to make air completely free from carbon dioxide 

 by the ordinary method, i.e., by merely passing it through 

 several alkaline bottles or alkaline towers. A simpler 

 and surer method is shown together with apparatus III in 

 Fig. 5 (p. 13 1) . It is prepared by shaking air with a 20 per 

 cent solution of sodium hydroxide in a tightly stoppered 

 carboy F, supplied with suitable tubes, one of which is 

 led to another carboy E, which is filled with about 10 

 to 15 per cent alkali solution. When the air in carboy 

 F is to be used, it is driven into the nitrometer C (appa- 

 ratus III) or W (in case of the biometer), which is filled 



