Adknky and Becker — Solution of Nitrogen and Oxygen. 617 



2. Absorption of air during periods of manipulation. 



3. Difference in temperature between the air in the bubble and that in 

 the air-space of the manometer. 



Of these it seemed that No. 1 was the most important ; No. 3 was 

 extremely small ; while subsequent experiments have shown that No. 2 is 

 negligible, with a narrow tube, such as was used in these experiments. 



In order to eliminate these errors it was decided to make a new form of 

 apparatus, suitable for use with a pure gas, such as nitrogen or oxygen ; and 

 to work with air-free water. 



(a) Preparation of Air-free Water. 



In order to ensure that the water was air-free, it was necessary to boil it 

 in the vacuum of the mercury pump, and then transfer it to the experi- 

 mental tube without allowing it to come in contact with the air. At first it 

 was thought that it would be sufficient to heat the water until its vapour- 

 pressure was great enough to force it over into the tube, but it was found 

 that this necessitated much too high a temperature. It was decided to 

 displace the water with mercury, but this introduced such a narrow tube 

 between the flask and condenser that the condensed vapour blocked it. 



The difficulty was finally solved by providing a second tube to allow the 

 water condensed to flow back into the flask. It was thus possible to boil 

 the water in vacuo as long as might be necessary, without any appreciable 

 loss by evaporation. 



The diagram (fig. 4) shows the form of apparatus used, and the mode of 

 operation is as follows : — The water in A is heated to a fairly high tempera- 

 ture by means of a water-bath, and the mercury pump is then worked until 

 a very low pressure is reached. In this way most of the gas is extracted in 

 the first violent ebullition, and the remainder is removed by continued 

 boiling under the reduced pressure. During the latter part of the operation 

 the water bumps very violently, with the result that some of it is thrown 

 over into the vessel E; but this returns to the flask immediately by the 

 tube B, as also does any water dripping from the condenser. When all the 

 air is extracted, the pinch-cocks B and C are closed, and D is opened, when 

 the mercury flows in and displaces the water into the experimental tube, 

 which has been previously filled with mercury, and connected to the flask A 

 by another tube not shown in the drawing. All the rubber stoppers used 

 were protected from leakage by mercury traps, and the rubber tubing was 

 varnished with shellac to prevent diffusion. 



SCIENT. PKOC. R.D.S., VOL. XV., NO. XLIV. 5 E 



