Note 171 — Chapter VII · New Process for the Manufacture of Beer.

M. Schützenberger applies the term saturated to a solution of hydrosulphite 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. (3-½ 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 supernatant 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.