STUDIES ON FEKMENTATION. 357 



act on a known volume of pure water saturated with oxygen 

 at a certain temperature. The tables of solubility of oxygen in 

 water give the exact volume of oxygen on which the measured 

 volume of hydrosulphite used has acted. According to Bunsen, 

 about one minute's brisk shaking in a closed bottle, with excess 

 of air, will be sufficient to effect the maximum saturation of 

 the water at the temperature at which we operate. 

 For experiments on wort we require : — 



1. A 2-litre (3i pints) flask, A, containing saturated hydro- 

 sulphite of soda,* of such strength that 2"5 c.c. will be sufficient 

 to absorb almost all the oxygen in 50 c.c. of water saturated 

 with air at the ordinary temperature (that is, 1 volume of hypo- 

 sulphite must equal 20 volumes of water). 



2. A 2-litre flask, B, containing a solution of indigo-carmine, 

 50 c.c. of which will be decolourized by about 20 c.c. of the 

 hydrosulphite. This solution contains about 20 grammes (30'7 

 grains) of commercial indigo-carmine per litre (1'76 pints). 



3. An apparatus, C, for the production of hydrogen. 



4. An experimental apparatus composed of a burette, D, 

 graduated in tenths of a cubic centimetre, and a three-necked 

 Wollf's bottle, E. 



5. A flask, F, holding about 100 c.c. provided with a straight 

 tube divided into tenths of a cubic centimetre, and containing a 



* M. Schlitzenberger ajiplies the term saturated to a solution of hydro- 

 sulph-ite prepared thus, or very nearly so : a current of sulphurous acid 

 is passed through a solution of commercial bisulphite of soda, to excess ; 

 100 c.c. (3^ fl. oz.) of this solution and 30 grammes (46 grains) of zinc 

 filings are put into a small flask, so as to completely fill it ; the bottle is 

 corked up and the mixture is shaken briskly for about a quarter of an hour. 

 Lastly, the contents of this flask are poured into a large 2-litre flask, 

 with water and containing milk of lime, prepared by mixing 100 grammes 

 (3"2 troy oz.) of quicklime in the water just before it is used. The whole 

 is shaken briskly for some minutes and then left to settle. The super- 

 natant liquid soon becomes bright. This is the hydrosulphite; but in 

 this state it is too concentrated ; and should be syphoned into another 

 2-litre flask half full of water. In the alkaline condition this salt 

 absorbs gaseous oxygen much less rapidly than in the acid, so that the 

 liquids will retain their strength much longer, if they are kept in well- 

 corked bottles. 



