136 Proceedings of the Royal Irish Academy. 



oxygenated liquids.^ As the estimation is made without the removal 

 of the oxygen by boiling, and in the condition in which it exists in 

 the water, such a plan would seem to be more desirable than its ex- 

 pulsion from the liquid, together with the other gases held in solution, 

 and their subsequent determination. 



I now proceed to give the results I have obtained by means of this 

 volumetric process. 



Briefly described, the method consists in adding a known volume 

 of the water under experiment to a solution which is capable of being 

 oxidized (accompanied by a change of colour due to such oxidation) by 

 the oxygen held in solution. The extent to which this has occurred 

 is then determined, by the addition of a powerful reducing agent, 

 which, acting upon the coloiu'ed compound so formed, reduces it to its 

 former condition — the amount necessary being, of course, indicated by 

 the reverse change of colour to that which occurred in the first in- 

 stance. This last solution being standardized in terms of the oxygen 

 it is capable of taking up, from the amount used in the experiment 

 we arrive at the volume of oxygen contained in the volume of water 

 taken. 



The re-agents used I will now describe, with the method, and 

 proportions for their preparation I found most advantageous. 



The reducing agent used is sodium hyposulphite — not the com- 

 monly so-called "hyposulphite," but the sodium salt of the acid 

 H2 SO3 ; its formula as given by Schutzenberger is ISTa H SOo. I 

 prepared this as follows : — A concentrated solution of caustic soda 

 (KaHO), specific gravity 1*4, was taken; sulphurous anhydride (SOo) 

 was passed through it, until the liquid was thoroughly saturated, and 

 smelt strongly of the gas. The yellow liquid (which was kept cool 

 during the process of saturation by immersion in cold water) is sodium 

 bisulphite (NaH SO3) ; it increased slightly in bulk, and was reduced 

 to the specific gravity of about 1'34. 100 grammes (75 cub. cents.) of 

 this solution was then briskly agitated in a flask with 6 grammes of 

 powdered zinc, air being excluded ; an elevation of temperature 

 occurred, the bisulphite being converted partly into the hyposulphite, 

 together with the formation of sodium sulphite and zincic sulphite, 

 according to the following equation : 



3 NaH SO3 + Zn = Na H SOo + ^a. SO3 + Zn SO3 + KO. 



After agitation for about five minutes, the liquid was allowed to cool; 

 400 cub. cents, of water recently boiled were added ; 35 cub. cents, of 

 milk of lime, containing 200 grammes of CaO per litre, were also 

 added, and the mixture allowed tP stand until clear, when it was 

 decanted off into well-stoppered bottles, and kept in the dark. 

 The lime solution not only precipitates the zinc salt, but also 



1 Bulletin de Chemie et Fhifsique, v01.'*k. 



