Solution of Atmospheric Nitrogen and Oxygen by Water. 3 1£ 



preliminary experiments were made with certain organic 

 dyestuffs, including , methylene blue, indigo, and indigo- 

 carmine, after reduction with suitable reagents, but the 

 results obtained were riot encouraging. Alkaline pyrogallol 

 was also tried, but with like results. 



On the whole, it was concluded that no very simple method 

 of estimating oxygen in this way could be devised which 

 could be relied upon to give results of the accuracy required 

 in the investigation. 



Letts's method of estimating oxygen with ferrous sulphate 

 was then tried, and gave good results, when the water 

 examined was nearly saturated with the gas ; but the exposure 

 of the water to the air during manipulation introduced 

 errors, which could not be regarded as negligible, when the 

 analyses were made during the earlier stages of re-aeration. 



Since these methods proved inapplicable, it only remained 

 to make the analyses by means of an extraction pump and 

 eudiometer in the usual way. This method had also the 

 advantage of affording a check on the estimation of oxygen, 

 since the determination of the dissolved nitrogen and 

 carbon dioxide could be included with but little additional 

 labour. 



The apparatus employed was a modification of the form 

 described by one of the authors in the Supplementary 

 Volume YI. to the Fifth Report of the Royal Commission 

 on Sewage Disposal, p. 96*. It consists of a mercury-pump 

 and a eudiometer, as shown in figs. 1 and 2. The pump 

 was prepared for use by placing in the laboratory flask a 

 small amount of water, acidulated with sulphuric acid, and 

 boiling this until the steam had driven most of the air out of 

 the flask. The flask was then raised, and the cork well 

 forced into the neck so as to make a vacuum -tight joint, this 

 being ensured by placing a little mercury in the annular 

 space above the cork. The mercury -pump was then worked 

 until no air could be detected after a lull stroke of the pump, 

 the water in the laboratory flask being kept boiling all the 

 time, and cold water running through the condenser. 



The water to be examined was then drawn into the pump 

 through the second capillary, the volume being noted by 

 means of two marks on the narrow necks of the bulbs, one 

 at 50 cc, and the second at 250 cc. 



A short length of thick-walled rubber tubing, one end of 

 which had been rounded by melting its edges in a Bunsen 

 flame, was slipped over the end of the capillary, and all 



* See also Proceedings Rov. Dubl. Soc. 1890, p. 542. 



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