GENERAL DESCRIPTION OP RESPIRATION APPARATUS. 75 



the meter registers 10 liters. By raising the reservoir E the air supply is 

 shut off, and after closing the stop-cock at C the tubes are disconnected, a 

 second set is put in place, and the operation repeated. The U -tubes are of 

 a size having a total length of the glass portion equal to 270 millimeters 

 and an internal diameter of 16 millimeters. They permit the passage of 

 3 liters of air per minute through them without a noticeable escape of 

 water-vapor or carbon dioxide. The U-tubes filled with pumice-stone and 

 sulphuric acid weigh 90 grams. They are always weighed on the balance 

 with a counterpoise, but no attempt is made to weigh them closer than to 

 0.5 milligram. 



GAS-METER. 



The gas-meter is made by the Dansk Maalerfabrik in Copenhagen, and 

 is of the type used by Bohr in many of his investigations. It has the 

 advantage of showing the water-level, and-the volume may be read directly. 

 The dial is graduated so as to be read within 50 cubic centimeters. 



The Elster meter formerly used for this purpose was much smaller than 

 the meter of the Dansk Maalerfabrik we are now using. The volume 

 of water was much smaller and consequently the temperature fluctuations 

 much more rapid. While the residual analyses for which the meter is used 

 are of value in interpolating the results for the long experiments, and 

 consequently errors in the meter would be more or less constant, affecting 

 all results alike, we have nevertheless carefully calibrated the meter by 

 means of the method of admitting oxygen from a weighed cylinder.* The 

 test showed that the meter measured 1.4 per cent too much, and conse- 

 quently this correction must be applied to all measurements made with it. 



* Francis G. Benedict: A method of calibrating gas-meters. Physical Review, 

 vol. 22, p. 294. (1906.) 



