There is always, however, more or less water vapor escaping with the alcohol and consequently it is impossible to secure absolute alcohol without after-treatment, although in the modern still a very high grade is often recovered in the first distillation. In this connection the strength of alcohol is usually determined by referring it to "proof," which is an old English system used before modern methods of testing spirits were available. In its original application, gunpowder was moistened with the spirit and the mixture subjected to the flame of a match. When just enough alcohol was present to set fire to the powder, it was said to be "proof spirit." If not enough alcohol was present to accomplish this, it was said to be "under proof," and when the gunpowder was lighted easily by it, it was said to be "over proof." By an act of the English Parliament, the term "proof spirit" was fixed as one which contains exactly 12/13 of an equal volume of water (distilled) at 51° F., which represents 57.1 per cent of alcohol by volume, or 49.3 per cent by weight. The simplest method of determining the percentage of alcohol is by the use of a gravity spindle for liquids lighter than water, and by referring to the accompanying table for this purpose, the percentage of alcohol may be ascertained. Table for calculating the percentage of alcohol. [5] =================================================================================================== |Specific gravity| |Specific gravity| |Specific gravity| |Specific gravity | at-- | | at-- | | at-- | | at-- Volume.|----------------|Volume.|----------------|Volume.|----------------|Volume.|---------------- | 15.56° 25° | | 15.56° 25° | | 15.56° 25° | | 15.56° 25° | 15.56 15.56 | | 15.56 15.56 | | 15.56 15.56 | | 15.56 15.56 --------------------------------------------------------------------------------------------------- | | | | | | | P. ct.| | P. ct.| | P. ct.| | P. ct.| 1 | 0.9985 0.9970 | 26 | 0.9698 0.9655 | 51 | 0.9323 0.9246 | 76 | 0.8745 0.8665 2 | .9970 .9953 | 27 | .9691 .9646 | 52 | .9303 .9225 | 77 | .8721 .8641 3 | .9956 .9938 | 28 | .9678 .9631 | 53 | .9283 .9205 | 78 | .8696 .8616 4 | .9942 .9922 | 29 | .9665 .9617 | 54 | .9262 .9184 | 79 | .8664 .8583 5 | .9930 .9909 | 30 | .9652 .9603 | 55 | .9242 .9164 | 80 | .8639 .8558 6 | .9914 .9893 | 31 | .9643 .9594 | 56 | .9221 .9143 | 81 | .8611 .8530 7 | .9898 .9876 | 32 | .9631 .9582 | 57 | .9200 .9122 | 82 | .8581 .8500