deprive it of as much carbonic acid as possible, then take the specific gravity at 15°5, and boil a third of the beer away in an open beaker. To make up the boiled beer to exactly the original quality again, take the specific gravity, and calculate as described at p. 379. (2.) The carbonic acid which the beer holds dissolved is most readily estimated by placing 100 cc. (or any convenient quantity) in a flask in connection with the Fox-Lane mercury pump described at p. 72; collecting the gases, and estimating the carbon dioxide in the usual way by absorbing it by caustic potash, and measuring the volume of gas before and after absorption. Another method is as follows:-A flask provided with a caoutchouc stopper, and carrying a tube twice bent at right angles, is connected with a smaller flask, containing strong ammonia water, into which the tube dips. This second flask must also carry a caoutchouc stopper, which should be doubly perforated, the one hole for the tube already mentioned, the other provided with a short, wide tube, packed with glass wool moistened with ammonia water. The beer must first be gently warmed and ultimately boiled, when the whole of the carbonic acid is absorbed by the ammonia. A sufficient quantity of a solution of calcium chloride is now added, the liquid boiled until all free ammonia is expelled, and the calcium carbonate thrown on a filter and washed. Lastly, the washed calcium carbonate is dissolved in either standard or decinormal acid, according to the quantity, a little cochineal solution is added, and the acid titrated back. 2 cc. of decinormal acid equal 10 mgrms. of carbonate of lime, or 44 mgrms. of CO2. This simple process is applicable to all liquids from which carbonic anhydride can be expelled by boiling. (3.) Volatile and Fixed Acids.-The acetic acid is obtained by distilling the beer nearly to dryness, and estimating the acidity of the filtrate by decinormal solution of soda.. Should the residue in the flask or retort be still acid, a little water should be added, and the distillation again continued to dryness; any acid now remaining is certain to be a fixed acid, probably lactic. It may be estimated by titration, and returned as lactic. The equivalent of anhydrous lactic acid is 90; hence 1 cc. of d. n. soda 9 mgrms. of lactic acid. Should it be specially necessary to determine the percentage of lactic acid, a sufficient quantity of beersay 300 cc.-is taken, evaporated to a small bulk, diluted with water, filtered, and mixed with a little sulphuric acid; pure carbonate of baryta is now added, and the whole warmed on the water-bath for some time. The liquid is then freed from the precipitate of sulphate of baryta by filtration, and the pre cipitate well washed with hot water. This filtrate is evaporated to a syrup, and treated, when cold, in a tube or separatingfunnel with a mixture of one part of sulphuric acid, one of water, one of alcohol, and ten of ether; the ethereal layer is separated in the usual way, and evaporated. The lactic acid thus obtained is still impure, and it is best to dissolve in water, saturate with freshly-precipitated carbonate of zinc, and estimate as zinc lactate, the latter containing 54:49 per cent. of anhydrous lactic acid. In most cases, however, the error will not be great, if the total acidity of the beer is taken directly without distillation, and returned as acetic acid. (4.) The Malt Extract.-The extract of beer can be determined by evaporating down a carefully measured quantity, and weighing the dry residue. In order to do this with any approach to accuracy, the smallest possible quantity should be taken-5 cc. or 5 grms. is quite sufficient. This small quantity, spread out as a thin film on the bottom of a tolerably capacious platinum dish, can be thoroughly dried over the water-bath in two or three hours, while if such quantities as 25 cc., 50 cc., or 100 cc. are taken, to get the extract completely dry is very tedious, and usually requires a higher temperature than 100°. It is, however, found in practice much more convenient to dispense with this drying altogether, the alcohol and carbonic acid being driven off, as before described, the beer made up to its first bulk, the specific gravity taken, and the amount of malt extract determined by the aid of the following tables. If the beer has been distilled, the residue in the retort or flask can be made up to the original bulk, brought to the proper temperature, and treated as just described. The alcoholic strength, the acetic acid, and the amount of malt extract being known, the analyst can now give a fairly approximate estimate of the amount of malt originally used in the brewing of the beer. To do this it is necessary to calculate the "original gravity" of the beer. The specific gravity of the alcoholic distillate (or, if an indirect process has been used, the specific gravity of the alcoholic strength) subtracted from 1000, gives a number called the "spirit indication." The degrees of gravity lost are then ascertained by the aid of the following tables, using the first if the beer has been distilled, and the second if the evaporating process has been used. The degrees of gravity thus found are added to the specific gravity of the boiled beer, and the number thus obtained is called "the original gravity of the wort." On reference to Table XL., the amount of malt extract is determined, which corresponds to this original gravity. TABLE XL-SPECIFIC GRAVITY AND STRENGTH OF MALT EXTRACT. Specific Malt Specifle Malt Specific Malt Specific Malt Gravity. Extract. Gravity. Extract. Gravity. Extract. Gravity. Extract. |