1·061 | 14·904 1·062 | 15·139 1·063 | 15·371 1·064 | 15·604 1·065 | 15·837 1·066 | 16·070 1·067 | 16·302 1·068 | 16·534 1·069 | 16·767 1·070 | 17·000 ----------+------------- The sugar contained in beer is best determined by by taking 50 c.c. of the sample, adding 10 c.c. of plumbic basic acetate solution, and making the volume of the mixture up to 300 c.c. with distilled water. After standing for some time the solution is passed through a dry filter. It is then examined by cautiously adding it from a burette to 10 c.c. of Fehling’s solution (diluted with 40 c.c. of distilled water and brought to the boiling-point), until the blue colour of the latter disappears (see p. 111). It should be borne in mind that, while 10 c.c. of Fehling’s solution are reduced by 0·05 gramme of glucose, it requires 0·075 gramme of maltose to effect the same reduction. In order to estimate the dextrine, 10 c.c. of the beer are reduced by evaporation to about 4 c.c., and heated with 1 c.c. of dilute sulphuric acid to 110° by means of an oil-bath in a strong hermetically closed glass tube for five hours. At the completion of this operation the solution is neutralised with sodium hydroxide, diluted, and the total glucose determined by Fehling’s reagent, as just described. The glucose due to the conversion of the dextrine is found by deducting the amount of maltose (expressed in terms of glucose) previously obtained from the total glucose; 10 parts of glucose represent 9 parts of dextrine. The organic acids (acetic and lactic) are estimated as follows:--(_a_) _Acetic acid_, by distilling 100 c.c. of the sample almost to dryness, and titrating the distillate with decinormal soda solution; (_b_) _Lactic acid_, by dissolving the residue remaining after the distillation in water, and either determining its acidity by decinormal soda, or by treating the residue with water and a little sulphuric acid, adding barium carbonate to the mixture, heating in the water-bath and filtering, the precipitate being thoroughly washed with hot water. The filtrate is then concentrated to a syrup by evaporation, and agitated in a test-tube with a mixture of 1 part each of sulphuric acid, alcohol, and water, and 10 parts of ether. After standing at rest for some time, the ethereal solution is separated by means of a pipette and evaporated to dryness in a tared capsule. The residue (impure lactic acid) can be weighed, or it is dissolved in water, the solution treated with zinc carbonate, and the lactic acid determined as zinc lactate, which contains 54·5 per cent. of the anhydrous acid. Phosphoric acid may be estimated in the beer directly by first expelling the carbonic acid, then adding a small quantity of potassium acetate, heating, and titrating with a standard solution of uranium acetate, using potassium ferrocyanide as the indicator. It can also be determined gravimetrically in the ash.