ACCOUNTS, MEMORANDA AND TABLES. 165 



is for discounts and interest. Table IX (p. 192), which 

 shows the circumference and area of circles from i to 100 

 diameter, is continually in demand. A gasholder is 40 feet 

 diameter and 16 feet high required the content. The 

 area of a circle 40 feet diameter is shown to be 1,256*64, 

 and this quantity multiplied by 16 gives the content of 

 the holder. A run of foul main is 15 inches diameter by 

 90 feet long, required the superficial or cooling surface. 

 The circumference of a circle whose diameter is 15 is 

 47*124, and this, multiplied by the length in inches will 

 give the surface in square inches. The figures can be used 

 for any desired unit ; but if, as in the foregoing, there are 

 two different units, such as length in feet and diameter in 

 inches, both must be reduced to the lowest unit, viz., 

 inches. A tar well is 1 2 feet in diameter, what is the con- 

 tent per foot depth ? The area of a circle having a dia- 

 meter of 12 is 113*1, and this multiplied by 6*25 (approx- 

 imately the number of gallons in a cubic foot) gives the 

 content, in gallons, per foot depth. A quantity of one 

 dimension, such as length, is stated in lineal measure. A 

 quantity of two dimensions, such as area, in square 

 measure, and one of three dimensions, such as the content 

 of a gasholder or tank, in cube measure. 



Tables X and XI (pp. 193-4) are examples of another 

 kind of information. The specific gravity, or the strength 

 by hydrometer, being known, the percentage of pure sub- 

 stance is indicated. A sample of commercial oil of vitriol 

 is found to be reasonably pure and to indicate 147* on 

 the hydrometer. It contains 80 per cent, pure sulphuric 

 acid. A solution of sulphate of ammonia indicates 68*2 

 Twaddel. According to Table XI, the percentage of pure 

 sulphate present is 59. The use of Table XII (p. 195) is 

 described on page 97. 



