Solution of Atmospheric Nitrogen and Oxygen by Water. 327 



overnight. During 'the course of an experiment, the water 

 was allowed to siphon over through the water-jacket of the 

 apparatus continually. In this way it was found possible to 

 keep the temperature of the tube constant within 1° C. during 

 an experiment. 



The length of the bubble while in motion was measured by 

 taking a number of instantaneous photographs of it while it 

 travelled up to the tube. A millimetre scale engraved on glass 

 was placed in the same focal plane as the centre of the tube, and 

 an image of this scale appeared alongsid e the bubble on the plate. 



On comparing this scale with a standard millimetre scale, 

 it was found to be considerably in error, and means were 

 adopted to correct for this. 



By the use of a micrometer eyepiece in the microscope the 

 length of the bubble was read off on the scale photographed 

 on the plate. The two points corresponding to these readings 

 were found on the actual scale, and the distance between 

 them read by means of the standard millimetre scale and the 

 micrometer. In this way all errors due to the inaccuracy 

 of the scale used were eliminated. The mean of a series 

 of observations was taken as the true length of the bubble. 



Plate V. is a photograph of the bubble while in motion, 

 and shows the form it assumes while moving up the tube. 



Experiments were made with three classes of water, 

 namely, water distilled in vacuo, tap-water from the Dublin 

 Vartry supply, and sea-water. In each case two experiments 

 w r ere made under conditions as similar to each other as 

 possible, though it w^as unavoidable that the atmospheric 

 pressure and the temperature varied a little. 



The manometer readings were in all cases converted to 

 volumes at N. T. P., and these included all the gases absorbed 

 from the atmosphere during the experiment. The effect of 

 the C0 2 in the air is scarcely appreciable in the case of the 

 distilled water and of the sea-water. But in the case of 

 the Vartry water, the manometer observations indicate a 

 greater absorption of gases than in the case of the distilled 

 water. The analyses of the gases extracted in the two cases 

 show that this increased absorption w^as due to the formation 

 of carbon dioxide in minute quantities in the Vartry water, and 

 to the consequent fixation of an equivalent volume of dissolved 

 oxygen during the experiment — a result, it may be assumed, 

 due to slight oxidation of the humus in the Vartry water. 

 This water contains decided quantities of peaty matter*. 



The actual experimental results obtained, in the case of 

 distilled water, tap-water, and sea-water, are recorded in 

 Tables 1, 2, and 3. 



* See the Experiments on the fermentative properties of humus in 

 Avater, by one of the authors. Trans. Roy. Publ. Soe. 1895, pp. 598-616 ; 

 and 1897, pp. 269-281. 



