THE RESPIRATION APPARATUS. 37 



measured on B t are compared directly in order to determine the per- 

 centage. The analyses are always made in duplicate, and the figures, 

 it is found, are in general sufficiently accurate to warrant calculation 

 to the second or even third decimal place. 



It may be said of this apparatus that it might easily be made more 

 convenient and accurate. Designs for an improved form are now under 

 consideration. Inasmuch, however, as the apparatus gives excellent 

 service, it has not seemed advisable to delay other work for the inev- 

 itable period of experimentation that must always accompany the intro- 

 duction of a new form of apparatus. Furthermore, it is readily seen 

 that owing to the small percentage of nitrogen there might be a con- 

 siderable error in measuring the absolute volume of oxygen taken for 

 a sample without noticeable effect upon the final results. 



Preparation of the reagents. Inasmuch as large quantities of potas- 

 sium pyrogallate solution are used for the numerous oxygen analyses, 

 as well as in air analyses to be described beyond, incidental to a metabol- 

 ism experiment, we have found it advisable to prepare stock solutions 

 of potassium hydroxide and of pyrogallic acid that can be mixed in the 

 proper proportions as desired. 



The potassium hydroxide solution was formerly prepared by dissolv- 

 ing 2,400 grams of stick potassium hydroxide in 1,600 cc. of water. 

 This method, however, proved needlessly expensive, and moreover 

 demanded that special precautions be taken to make sure that the 

 "stick potash " had not been purified with alcohol, since, as Hempel 1 

 points out, the presence of small quantities of alcohol may be a serious 

 source of error. It was found that a grade of commercial caustic potash, 

 sold by the Roessler & Hasslacher Chemical Company, of New York, and 

 costing about 7 cents per pound, could be substituted to good advantage. 

 Our present practice is to dissolve 2,400 grams of this potash in i ,750 cc. 

 of water and filter the solution when sufficiently cool through glass wool. 



In preparing the solution of pyrogallic acid 100 grams of the acid 

 are dissolved in 303 cc. of water, the mixture of acid and water being 

 well shaken until there is complete solution. 



These stock solutions are generally made up several days before they 

 are needed for use. 



The proportions in which the acid solution and the potassium hydrox- 

 ide solution are mixed are 7 cc. of the pyrogallic-acid solution to 44 cc. 

 of the potassium hydroxide solution. Two sizes of pipettes are regu- 

 larly used. The larger pipette requires 28 cc. of the acid and 176 cc. 

 of the alkali to fill it, the smaller 21 cc. of acid and 132 cc. of alkali. 

 The acid is placed in the pipette, a portion of the alkali added, and the 



1 Hempel, Gas Analysis, 1892, p. 115. 



