100 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



connections have been properly made and that the oxygen has been admitted 

 to the chamber in proper amount, the blower is again started. It is then 

 necessary to weigh the U -tubes and disconnect the old set of absorbers and 

 weigh them. If the sulphuric-acid absorbers have not exceeded the limit of 

 gain in weight they are used again ; if they have, new ones are put in their 

 place. 



The first sulphuric-acid absorber is connected to the front valve, then 

 the potash-lime can, and then the last sulphuric-acid absorber; but before 

 connecting the last sulphuric-acid absorber with the sodium-bicarbonate 

 can, a test is made of the whole system from the front valve to the end of 

 the second sulphuric-acid absorber. This is made by putting a solid-rubber 

 stopper in the exit end of the second sulphuric-acid absorber and, by means 

 of a bicycle pump, forcing compressed air in through a pipe tapped into 

 the pipe from the valve at the front end until a pressure of about 2 feet 

 of water is developed in this part of the system. This scheme for testing 

 and the method of connecting the extra pipe have been discussed in detail 

 in an earlier publication.* Eepeated tests have shown that this method of 

 testing the apparatus for tightness is very successful, as the minutest leak 

 is quickly shown. 



After the system has been thoroughly tested, the rubber stopper in the 

 exit end of the second sulphuric-acid absorber is first removed, then the 

 tube connected with the pump and manometer is disconnected and its end 

 placed in the reservoir of mercury. Occasionally, through oversight, the 

 pressure is released at the testing-tube with the result that the air com- 

 pressed in the system expands, forcing sulphuric acid into the valves and 

 down into the blower, thus spoiling completely the experiment. After the 

 testing, the last sulphuric-acid absorber is coupled to the sodium-bicarbo- 

 nate can. It is seen that this last connection is the only one not tested, and 

 it has been found that care must be taken to use only the best gaskets at 

 this point, as frequently leaks occur; in fact, it is our custom to moisten 

 this connection with soapsuds. If new rubber gaskets are used a leak is 

 never found. 



SUPPLEMENTAL APPARATUS. 



To maintain the apparent volume of air through the whole system con- 

 stant, oxygen is admitted into the tension-equalizer until the same tension 

 is exerted on this part of the system at the end as at the beginning. This 

 is done by closing the valve connecting the tension-equalizer with the sys- 

 tem and admitting oxygen to the tension-equalizer until the petroleum 

 manometer shows a definite tension. After the motor is stopped, at the 

 end of the experimental period, there is a small amount of air compressed 

 in the blower which almost instantly leaks back through the blower and the 

 whole system comes under atmospheric pressure, save that portion which 



* Atwater and Benedict: hoc. cit., p. 21. 



