45, CORNHILL, E.G., AND 122, REGENT STREET, W., LONDON. 



179 



FIG. 429. FIG. 429*. 



sink it will determine the selection of the requisite weight to be attached to the 

 lower stem. Again immerse the hydrometer in the spirit, and allow it to float 

 freely and settle, and then keeping the eye in a line with the surface of the spirit, 

 notice the division cut by the surface as seen from below. The number indicated 

 by the stem is added to the numbers of the weight, and the sum of these, together 

 with temperature of the spirit (which should be very carefully noted) will, by 

 reference to a Book of Tables accompanying the instrument, give the required 

 strength per cent, of the spirit under test. 



The strength is expressed in numbers denoting the excess or deficiency per 

 cent, of proof spirit in any sample, and the number itself having its decimal point 

 removed two places to the left, becomes a factor, whereby the gauged contents of 

 a cask of such spirit being multiplied, and the product being added to the gauged 

 contents if over proof, or deducted from it if under proof, the result will be the 

 actual quantity of proof spirit contained in such vessel. 



The commercial term above or below proof is partly derived from the govern- 

 ment having fixed a certain strength of spirit as mentioned above as Proof Spirit 

 by which the strength of all spirit is comparable. It is also said that the term 

 proof is derived from an ancient method of testing the strength of spirit by pouring 

 the sample over gunpowder in a metal cup and then setting fire to the spirit ; if, 

 when the spirit had burnt away, the powder exploded, the spirit was said to be over 

 proof; if , on the other hand, the gunpowder did not ignite, owing to the large 

 portion of water left behind, it was said to be under proof. 



The weakest spirit capable of firing gunpowder by this method was called proof 

 spirit, but it required a spirit of nearly the strength of what is now called rectified 

 spirit to stand this test. 



The Standard Proof Spirit of the excise is defined by law (56 Geo. III. cap. 

 140) to be " that which at a temperature of 51 Fahrenheit's Thermometer, weighs 

 exactly twelve-thirteenth parts of an equal measure of distilled water" 



This will have a specific gravity of '923 at 51 Fahrenheit, or about -920 at 60 

 Fahrenheit. 



The Standard Alcohol of the Excise is spirit of the specific gravity '825 at 60 Q 

 Fahrenheit. By " Spirit 60 degrees over proof " is understood a spirit 100 measures 

 of which added to 60 measures of water will form Standard Proof Spirit, specific 

 gravity '920. 



By " Spirit 10 degrees under proof " is understood a spirit 100 measures of 

 which mixed with 10 measures of standard alcohol, specific gravity '825, will form 

 Standard Proof Spirit. 



NOTE. We are indebted to Professor Bed wood for most of the figures given in connection with 

 Sikes' Hydrometer. The British Pharmacopoeia of 1864 orders that the Specific Gravity of liquids is to be 

 taken at a temperature of 60 degrees by Fahrenheit's Thermometer, and gives the Specific Gravity of 

 absolute Alcohol as 0795, Rectified Spirit (Spiritus Eectificatus) as 0'838. and Proof Spirit ( Spiritus Tenuior) 

 as 0-920, at a temperature of 60 degrees Fahrenheit. 



N 2 



