(_a_) _Alcohol._--In properly distilled liquors, a fairly approximate estimation of their alcoholic strength is effected by the specific gravity determination, which is best made by means of the special gravity bottle. In the case of spirituous liquors which contain extractive matters, it is necessary to first separate the alcohol present by the process of distillation, and then determine the density of the distillate when made up to the volume originally taken. The following table gives the percentages of alcohol by weight and by volume, and of water by volume, for specific gravities at 15°.[117] The percentages of alcohol in the table are calculated for the temperature of 15°. The necessary correction for differences of temperature at which the determination is made is obtained by multiplying the number of degrees above or below 15°, by 0·4, and adding the product to the percentage shown by the table, when the temperature is lower than 15°, and deducting it when it is above. Percentage of alcohol, by weight and by volume, and of water by volume, for specific gravity at 15°; water at same temperature being the unit:-- ---------+------------------------- | PERCENTAGE. +---------+--------------- | By | By | Weight. | Volume. Specific +---------+------+-------- Gravity. | Alc. | Alc. | Water. ---------+---------+------+-------- 1·0000 | 0· | 0 | 100· 0·9985 | 0·80 | 1 | 99·05 0·9970 | 1·60 | 2 | 98·11 0·9956 | 2·40 | 3 | 97·17 0·9942 | 3·20 | 4 | 96·24 0·9928 | 4·00 | 5 | 95·30 0·9915 | 4·81 | 6 | 94·38 0·9902 | 5·61 | 7 | 93·45 0·9890 | 6·43 | 8 | 92·54 0·9878 | 7·24 | 9 | 91·62 0·9867 | 8·06 | 10 | 90·72 0·9855 | 8·87 | 11 | 89·80 0·9844 | 9·69 | 12 | 88·90 0·9833 | 10·51 | 13 | 88·00 0·9822 | 11·33 | 14 | 87·09 0·9812 | 12·15 | 15 | 86·19 0·9801 | 12·98 | 16 | 85·29 0·9791 | 13·80 | 17 | 84·39 0·9781 | 14·63 | 18 | 83·50 0·9771 | 15·46 | 19 | 82·60 0·9761 | 16·29 | 20 | 81·71 0·9751 | 17·12 | 21 | 80·81 0·9741 | 17·96 | 22 | 79·92 0·9731 | 18·79 | 23 | 79·09 0·9721 | 19·63 | 24 | 78·13 0·9711 | 20·47 | 25 | 77·23 0·9700 | 21·31 | 26 | 76·33 0·9690 | 22·16 | 27 | 75·43 0·9679 | 23·00 | 28 | 74·53 0·9668 | 23·85 | 29 | 73·62 0·9657 | 24·70 | 30 | 72·72 0·9645 | 25·56 | 31 | 71·80 0·9633 | 26·41 | 32 | 70·89 0·9620 | 27·27 | 33 | 69·96 0·9607 | 28·14 | 34 | 69·04 0·9595 | 29·01 | 35 | 68·12 0·9582 | 29·88 | 36 | 67·20 0·9568 | 30·75 | 37 | 66·26 0·9553 | 31·63 | 38 | 65·32 0·9538 | 32·52 | 39 | 64·37 0·9522 | 33·40 | 40 | 63·42 0·9506 | 34·30 | 41 | 62·46