60 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



POTASH-LIME CANS. 



The problem of absorbing the water-vapor from so rapid a current of air 

 is second only to that of absorbing the carbon dioxide from such a current. 

 All experiments with potassium hydroxide in the form of sticks or in solu- 

 tion failed to give the desired results and the use of soda-lime has supple- 

 mented all other forms of carbon dioxide absorption. More recently we 

 have been using potash-lime, substituting caustic potash for caustic soda in 

 the formula, and the results thus obtained are, if anything, more satisfac- 

 tory than with the soda-lime. 



The potash-lime is made as follows : 1 kilogram of commercial potassium 

 hydroxide, pulverized, is dissolved in 550 to 650 cubic centimeters of water 

 and 1 kilogram of pulverized quicklime added slowly. The amount of 

 water to be used varies with the moisture content of the potash. There is 

 a variation in the moisture content of different kegs of potash, so when a 

 keg is opened we determine experimentally the amount of water to be used. 

 After a batch is made up in this way it should be allowed to cool before 

 testing whether it has the right amount of water, and this is determined by 

 feeling of it and noting how it pulverizes in the hand. It is not advisable 

 to make a great quantity at once, because we have found that if a large 

 quantity is made and broken into small particles and stored in a container 

 it has a tendency to cake and thus interfere with its ready subsequent use. 



A record was kept of the gains in weight of a can filled with potash-lime 

 during a series of experiments where there were three silver-plated cans 

 used. This can was put at the head of the system and when it began to 

 lose weight it was removed. The records of gains of weight when added 

 together amount to 400 grams. From experience with other cans where 

 the loss of moisture was determined, it is highly probable that at least 200 

 grams of water were vaporized from the reagent and thus the total amount 

 of carbon dioxide absorbed must have been not far from 600 grams. At 

 present our method is not to allow the cans to gain a certain weight, but 

 during 4-hour or 5-hour experiments, in which each can may be used 2 or 

 3 hours, it is the practice to put a new can on each side of the absorber 

 system (see page 66) at the beginning of every experiment. This insures 

 the same power of absorption on each side of the absorption system, so that 

 the residual amount of carbon dioxide in the chamber from period to period 

 does not undergo very marked changes. This has been found the best 

 method, because if one can is left on a day longer than the other there is 

 apt to be alternately a rise and fall in the amount of residual carbon dioxide 

 in the apparatus, owing to the unequal efficiency of the absorbers. 



These cans are each day taken to the basement, where the first section * 



* For a description of the apparatus and the method of filling see W. O. At- 

 water and F. G. Benedict: A respiration calorimeter with appliances for the 

 direct determination of oxygen. Carnegie Institution of Washington Publication 

 No. 42, p. 27. (1905.) 



