314 Hydrostatics. 



0,83 and water 1 ; we have in this case 



S = 0,83, S' = 1, and S" = 0,93, 

 which gives, 



S' S" = 0,07, S" S = 0,1, 



and by substitution, 



6:6':: 0,07 : 0,10 ; 



that is, the proportion by measure of pure spirit to that of water, 

 is as 7 to 10. In what is called proof spirit, it is required that 

 the constituent parts of water and spirit, should be equal, which 

 gives a specific gravity of 0,925, and the degree above or below 

 proof is usually denoted by the number of gallons of water to be 

 added to or taken from 100 gallons of the liquor in question, to 

 bring it to the required standard or proof. 



But more expeditious methods have been devised for deter- 

 mining the proportion of alcohol in spirits. It is evident that if 

 a great variety of mixtures of known proportions were prepared, 

 and hollow glass balls or beads were so adapted to each in res- 

 pect to specific gravity, as just to remain suspended in any part 

 of the fluid ; by marking the known proportion of alcohol and 

 spirits in each case on the respective balls, similar unknown 

 mixtures might be readily examined as to their proportion of 

 alcohol. It would only be necessary to make trial of different 

 balls until one was found which would tend neither to rise nor 

 sink when immersed in the fluid. But instead of a large number 

 of such balls, a single one with a long graduated stem and move- 

 able weights, as represented in figure 211 might be employed to 

 the same purpose. The ball itself should be of such a specific 

 gravity as just to sink to the commencement of the graduation on 

 the stem when suspended in alcohol, and the weights to be at- 

 tached should be such as to cause the ball and some part of the 

 stem to sink in any mixture of less specific gravity than pure 

 water. Then the weight together with the divisions of the stem, 

 which serve to subdivide the difference between two weights, 

 would indicate, like the separate balls, the specific gravity of the 



