100 Composition or the Atmosphere 



FIFTH ROUTINE, AND RESULTS OBTAINED. 



A final change in the routine was made on April 15, 191 1 . When using 

 a layer of 17 mm. of water in the capillary tube of pipette B it was found 

 that variations in the percentage of oxygen in cylinder air were occasion- 

 ally experienced which were somewhat greater than it was believed the 

 method should allow. A few preliminary tests indicated that more uni- 

 form conditions of moisture in the pipette could be obtained by another 

 procedure, and the following routine has since been adopted: 



Outline of fifth routine. The nitrogen remaining from the earlier 

 analysis having been stored over the potassium hydroxide and potassium 

 pyrogallate, the stop-cock b is closed and the plug of stop-cock a is with- 

 drawn. The pipette B is first completely filled with mercury. Water 

 is then introduced through the open stop-cock a, exactly as in the pre- 

 ceding routine, and the mercury in pipette B simultaneously lowered, 

 thus drawing the water down through the capillary tube into the pipette. 

 This is continued until the mercury is lowered to the zero-point, and sev- 

 eral times the amount of water previously used has been introduced. 

 The whole interior of the pipette is thus thoroughly drenched with water. 

 The mercury is again raised, expelling all of the visible water, so that none 

 remains above the mercury, filter paper inserted in the cock opening being 

 used to remove the water. The stop-cock is then inserted, and the ni- 

 trogen is drawn from the two absorption pipettes, the levels of the potas- 

 sium hydroxide and potassium pyrogallate are set, and the analysis pro- 

 ceeds in the usual way, i.e., the carbon dioxide is absorbed by sending the 

 gas twice into the potassium hydroxide, taking but one final reading; the 

 air is next passed into the potassium pyrogallate for 5 minutes, then with- 

 drawn, and passed into the potassium hydroxide once. It is again drawn 

 back and passed into the potassium pyrogallate for 1 minute, then into 

 the potassium pyrogallate for 5 minutes, and into the potassium hydrox- 

 ide once. The level of the latter reagent is now set. The gas is finally 

 sent into the potassium pyrogallate for 1 minute, the level is set, and the 

 reading taken. All the capillaries now being filled with nitrogen as at the 

 beginning of the analysis, the contraction in volume represents the per- 

 centage of carbon dioxide in the air and the percentage of oxygen in 

 carbon-dioxide-free air. This routine, which has been followed without 

 any variation since April 15, 1911, has proved eminently satisfactory. 



Results with fifth routine. The results of the analyses of uncontami- 

 nated outdoor air between April 15, 1911, and January 9, 1912, as given 

 in table 61, are conclusive in showing that no fluctuation of any magnitude 

 occurs in the percentage of oxygen in air. Certain values lower than the 

 average may be almost invariably attributed to the fact that after new 

 potassium pyrogallate is placed in the reagent vessel the first analysis 

 is inclined to show a somewhat low percentage of oxygen. When it is 

 considered that all of the determinations, with the single exception of a 

 short series from September 15 to 25, 1911, are reported, the accidental 

 variations are indeed inconsiderable. 



