CALCULATION OF RESULTS. 91 



CALCULATION OF TOTAL OUTPUT OF CARBON DIOXIDE AND WATER- VAPOR 

 AND OXYGEN ABSORPTION. 



From the weights of the sulphuric-acid and potash-lime vessels, the 

 amounts of water-vapor and carbon dioxide absorbed out of the air-current 

 are readily obtained. The loss in weight of the oxygen cylinder increased 

 by 0.4 per cent (see page 88) gives the weight of oxygen admitted to the 

 chamber. It remains, therefore, to make proper allowance for the varia- 

 tions in composition of the air inside the chamber at the beginning and end 

 of the different periods. From the residual sheets the amounts of water- 

 vapor, carbonic acid, and oxygen present in the system at the beginning 

 and end of each period are definitely known. If there is an increase, for 

 example, in the amount of carbon dioxide in the chamber at the end of a 

 period, this increase must be added to the amount absorbed out of the air- 

 current in order to obtain the true value for the amount produced during 

 the experimental period. 



A similar calculation holds true with regard to the water-vapor and 

 oxygen. For convenience in calculating, the amounts of water-vapor and 

 carbon dioxide residual in the chamber are usually expressed in grams, 

 while the oxygen is expressed in liters. Hence, before making the additions 

 or subtractions from the amount of oxygen admitted, the variations in the 

 amount of oxygen residual in the system should be converted from liters 

 to grams. This is done by dividing by 0.7. 



CONTROL EXPERIMENTS WITH BURNING ALCOHOL. 



After having brought to as high a degree of perfection as possible the 

 apparatus for determining carbon dioxide, water, and oxygen, it becomes 

 necessary to submit the apparatus to a severe test and thus demonstrate 

 its ability to give satisfactory results under conditions that can be accu- 

 rately controlled. The liberation of a definite amount of carbon dioxide 

 from a carbonate by means of acid has frequently been employed for con- 

 trolling an apparatus used for researches in gaseous exchange, but this only 

 furnishes a definite amount of carbon dioxide and throws no light what- 

 ever upon the ability of the apparatus to determine the other two factors, 

 water-vapor and oxygen. Some of the earlier experimenters have used burn- 

 ing candles, but these we have found to be extremely unsatisfactory. The 

 necessity for an accurate elementary analysis, the high carbon content of 

 the stearin and paraffin, and the possibility of a change in the chemical 

 composition of the material all render this method unfit for the most 

 accurate testing. As a result of a large number of experiments with dif- 

 ferent materials, we still rely upon the use of ethyl alcohol of known water- 

 content. The experiments with absolute alcohol and with alcohol con- 

 taining varying amounts of water showed no differences in the results, and 



