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No. 30. 



A RAPID GASOMETRIC METHOD OF ESTIMATING DISSOLVED 

 OXYGEN AND NITROGEN IN WATER. 



By H. G. BECKER, AR.C.Sc.I., A.I.C., 



AND 



W. E. ABBOTT, A.R.C.Sc.I., A.I.C, B.Sc. 

 (Read June 26. Printed August 15, 1923.) 



Introduction. 



The transient milldness of water iu which potash is dissolving, due to minute 

 bubbles of dissolved air, suggested the possibility of utilising this phenomenon 

 for the estimation of dissolved gas. Consultation of the literature' encouraged 

 this view, since it appeared that the solubility of a gas in dilute solutions is 

 generally considerably less than in pure water. Wliile little was known regarding 

 the solubility of gas in concentrated solutions, it appeared probable that it 

 should be nearly zero in very concentrated solutions of certain electrolytes. It 

 was proposed, therefore, to work out a method whereby the water should be 

 brought in contact with the solid electrolyte under such conditions that the 

 displaced gas could be readily collected and measured. Preliminary attempts 

 made to displace the dissolved oxygen and nitrogen from tap-water showed that 

 the gas evolution was fairly complete, though rather slow at ordinary pressure. 

 With a view to hastening the process, it was considered advisable to arrange that 

 the gas should be liberated under a greatly diminished pressure. 



The choice of a solute was the first point to be considered. Caustic potash 

 had been shown by the preliminai'y experiments to be very good in most respects. 

 Owing to its high cost, however, attempts were made to find a cheaper substance 

 which would be equalty effective. Such materials as were not available in a 

 compact form suitable for testing were prepared for use in our apparatus by 

 fusion, and subsequent solidification. Caustic soda was as good as potash, except 

 for a tendency to crystallize and block the capillaries during manipulation. 

 Magnesium chloride, and calcium nitrate in large quantity expelled practically 

 all the dissolved gas, but at a very slow rate. Fused potassium chloride expelled 

 about 95 per cent, of the dissolved g8,s, but twenty to thirty minutes were 

 required for this evolution, as against one to two minutes when using potash. 

 Sodium sulphate, citric acid, calcium chloride, sodium carbonate, sodium thio- 

 sulphate, zinc chloride, and alum proved unsatisfactory. The rate of evolution 

 of gas when using potash or soda is very remarkably greater than that which 

 follows the use of any other of these materials. Glycerol, and strong sulphuric 

 acid in large amounts give a rapid and good, but possibly not quite complete, 

 evolution of gas. It was finally decided to adopt potash as the solute in the 

 absence of a satisfactory substitute; but we recognise that we have not investi- 

 gated the possibilities of substitutes as fully as we would desire. Thus it has 



le.g., G. Gefifcken Z. physik. Chem. 49, 271, 1907. 



SCIENT. PROC. R.D.S., VOL. XVII, NO. 30. 2z 



