80 Composition of the Atmosphere 



fig. 1. Care should be taken to prevent dust from entering the tube or 

 liquid, as it is liable to accumulate on the inside of the reservoir and ulti- 

 mately cause difficulty in reading the exact height of the liquid in the 

 capillary tubing. 



The solution for absorbing oxygen. Shortly after Liebig announced his 

 discovery of the fact that potassium pyrogallate absorbed oxygen quanti- 

 tatively, the criticism was raised by Calvert, Boussingault, and Cloez 1 

 that potassium pyrogallate, when reacting with oxygen, gave rise to the 

 formation of a certain amount of carbon monoxide, the evolution of this 

 gas naturally vitiating the results obtained by this method of analysis. 

 Several years later a further caution was published by Hempel to the 

 effect that one should not use potassium hydroxide "purified by alcohol" 

 in the preparation of the potassium pyrogallate. 2 In this defense of the 

 use of the pyrogallate solution, he also pointed out that if proper attention 

 was given to the concentration of the solution there need be no fear of 

 the evolution of carbon monoxide. 



When the formulas for preparing this solution are examined, it is 

 found that the main differences noted are in the proportion of water pres- 

 ent. When "a 60 per cent solution of caustic potash" is stated, one im- 

 mediately has to determine what is meant by "a 60 per cent solution." 

 Even when the weight of potassium hydroxide is given in the formula, 

 difficulty is experienced owing to the differences in water-content of the 

 substance, stick potassium hydroxide frequently containing as much as 

 25 per cent of water. Haldane's formula alone obviates this difficulty, 

 as he requires a fully saturated solution of potassium hydroxide with 

 a specific gravity of 1.55. Earlier experience with Haldane's formula, 

 however, showed that with a low room-temperature the material solidi- 

 fied; and with so delicate an apparatus as that of Sondn it seemed un- 

 desirable to introduce a reagent that might solidify and possibly burst 

 the glass container. 



Since the prime object of this research was a comparative study of the 

 oxygen content of the air, and since certain fundamental defects in the 

 apparatus prevented deductions regarding the exact absolute value, we 

 modified slightly Haldane's solution as follows: 



A solution of potassium hydroxide was prepared by dissolving 500 

 grams of stick potassium hydroxide, not purified by alcohol, in 250 c. c. 

 of water. Usually the specific gravity of the resulting solution was 1.55. 

 During the progress of this research, several shipments of stick potassium 

 hydroxide were used, and the varying water-content of the chemical is 

 shown by the fact that it was frequently necessary to add more potassium 

 hydroxide to bring the solution to the desired density. To 135 c. c. of this 

 saturated solution was added a solution of 15 grams of pyrogallic acid 



1 Calvert, Comptes rendus, 1863, 57, p. 873; Cloez, Comptes rendus, 1863, 57, p. 875; 

 Boussingault, Comptes rendus, 1863, 57, p. 885. 



s Hempel, Berichte der deutschen chemischen Gesellschaft, 1887, 20, p. 1865. 



