332 Dissolved Oxygen in Raln-ivater 



Humboldt and Gay-Lvissac^ found that the gas from aerated dis- 

 tilled water contained 32-9 per cent, of oxygen compared with 31-0 per 

 cent, in rain-water. Gerardin^ in two papers records figures which are 

 mostly below saturation. Reichard^ gives a series of analyses made at 

 Jena of which only one sample taken in January, at 4° C, is saturated 

 with oxygen. At the other extreme a sample in July, at 24° C, is only 

 62 per cent, saturated. 



The rain was collected at Rothamsted in two large glass funnels 

 10 inches diameter, the tubes reaching to the bottoms of two narrow- 

 mouthed bottles of about one litre capacity. They were supported in a 

 stand so that the rims of the funnels were 2 feet 6 inches above ground 

 level. At first the two collectors were used in duphcate to check the 

 results obtained, but as the figures for the two samples were invariably 

 identical, a layer of liquid paraffin was subsequently placed in one 

 bottle sufficient to cover the end of the funnel tube and protect the 

 surface of the rain as it collected from contact with the air. 



No determinations of dissolved oxygen were made on rainfalls 

 under 0-30 inch, as the size of the funnels was too small to yield the 

 necessary amount of sample. The bottles were of course emptied after 

 any rain and both these and the funnels were frequently cleaned. 



Table I. Dissolved Oxygen in mixtures of 1 per cent. Belfast Sewage 



with Tap-water and Sea-water kept in full stoppered bottles. 



Dissolved oxygen in c.c. per litre at n.t.p. Temperatures in ° F. 



When mixed After 5 days After 14 days After 42 days 

 at at at at 



60° 70° 80° 60° 70° ^0° 60° 70° ^° 60° 70° 80° 

 Tap-water mixture ; 



Oxygen (gasometric) 6-2 60 5-4 50 41 3-0 4-2 4-2 0-9 2-9 71 0-2 



Oxygen (Winkler)... 6-6 5-9 5-5 50 40 30 40 4-2 0-9 2-9 T-4 0-1 



Sea-water mixture : 



Oxygen (gasometric) 5-5 5-1 4-7 3-9 3-5 2-7 3-3 3-2 1-6 2-7 2-5 0-2 



Oxygen (Winkler)... 5-7 5-4 5-0 4-0 3-6 2-8 3-2 3-1 1-5 2-5 2-3 0-1 



Winkler's* method was used for estimating the dissolved oxygen. 



The author has had many years' experience of this method and has 



always found it entirely satisfactory. When properly carried out it 



gives results in close agreement with the best gasometric determina- 



, tions. Table I gives some comparative estimations made by Prof. Letts 



^ "Memoire sur rEudiometrie," Journal de Physique, 1805 



2 Compt. Rend. 75, 1872, p. 1713, and 81, 1875, p. 989. 



3 Archiv Pharm. 1875, 206; m, vol. vi, p. 193. 

 * Berichte, vol. xxx, pp. 2, 843 (1888). 



