The proportion of this constituent does not vary much in palatable beer, ranging from about 025 to 04 per cent. The taste alone is a good guide, as beer with less than 02 per cent. of carbon dioxide tastes " flat."

If the beer is in cask, a quantity of 200 to 300 grams is drawn off into a tared flask fitted with a "wash.bottle " arrangement of tubes, both closed with short pieces of rubber tubing carrying pinchcocks. By means of the cocks and an air-pump the pressure of air in the flask is reduced, to facilitate the taking of the sample. After weighing, the flask containing the drawn-off quantity is connected up with an apparatus of soda-lime tubes (or potash bulbs) for absorbing the carbon dioxide, similar to that described for the estimation of methyl alcohol by Thorpe and Holmes's method (p. 189). The pinchcock on the exit tube of the flask is opened very carefully at first to prevent too rapid escape of the carbon dioxide into the absorption tubes; then the flask is gradually heated to gentle boiling, to expel the carbon dioxide from the beer, and finally a current of air freed from carbon dioxide is aspirated through the flask, and the absorption tubes weighed: the increase in weight shows the weight of carbon dioxide in the sample.

If the beer is in bottle, the cork may be pierced with a champagne tap, or with a cork-borer, over the blunt end of which a piece of stout rubber tubing carrying a pinchcock has been passed. The tap, or the tube, as the case may be, is then connected with the absorption train, and the bottle placed in cold water. The tap or cock is opened cautiously, and when the gas has ceased to pass, the water is warmed slowly to about 80°, and kept at this temperature for about half an hour, the bottle being shaken frequently. At the end of this period the bottle is removed, and a current of air freed from carbon dioxide passed as before.

Bottles with screw stoppers may be cooled down in ice-water, and the stopper rapidly replaced by a rubber stopper fitted with a tube and pinchcock, or with a glass tap. Some gas will often escape - but this, after all, is what would happen, and to a greater extent, if the beer were poured out for drinking.

Proportion Of alcohol and "extract." - The experimental data furnished by the determination of the original gravity by the distillation process allow of these quantities being obtained. By referring the specific gravity of the distillate to the ordinary alcohol tables (p. 237), we get the proportion of alcohol.

Deducting 1000 from the specific gravity of the extract, and dividing the remainder by 3.86, the quotient denotes the grams of dry extract in 100 c.c. of the beer.

Further examination of the extract usually resolves itself into a determination of the reducing sugars in terms of maltose ("crude maltose," " apparent maltose "), the dextrinous matters ("apparent dextrin "), the proteids, and the ash.