138 Proceedings of the Royal Irish Academy. 



finite, and diflScult, even to the practised eye, to detect, that the exact 

 point cannot be determined with any degree of certainty. 



The second method consists in obtaining a pure water saturated 

 with air, and then finding the quantity of hyposulphite capable of 

 abstracting the whole of its oxygen. 



This water is obtained by agitating in a large flask about one litre 

 of distilled water with free access of air ; the agitation is continued 

 for about a quarter of an hour. To find the amount of oxygen in a 

 given volume of the water, I made the following formula, from the 

 consideration of the relative quantity of oxygen present in the air,, 

 and its coefiicient of absorption in water : 



P 



V = 0-0262 X a,o X r X — , 



9o 



in which we have 



V - vol. of oxygen in cub. cents, at 0° C. and 760 m.m.s. pres. 



ttfo = coefficient of absorption of oxygen in water at temp. t° C, given 

 by Bunsen's Tables. 



V - volume of water employed, temp. t° C. 



P = barometric pressure in m.m.s. 



The relation between the saturated water and the hyposulphite is 

 foTind in exactly the same way as the method, hereafter described, 

 for the oxygen determination in waters. I found that, although the 

 hyposulphite solution was about the strength recommended, the 

 volume relation between it and the indigo, instead of being one to ten, 

 was equal. As the indigo solution thus appeared ten times too con- 

 centrated, I further diluted it for use. 



The following is an example of standardization by the above 

 method. The apparatus was in every way regulated as described for 

 water estimations : — 



Comparison of Hyposidpliite^ md Indigo. 

 Mean of five experiments gave 



25 cub. cents, indigo = 7 cub. cents, hyposulphite. 



Comparison of Saturated Water and I^^&ulpMte. 

 Mean of five experiments gave 



75 cub. cents, of water = 2'4 cub. cents, hyposulx^hite, 



