This section is from the book "The Tinman's Manual And Builder's And Mechanic's Handbook", by Isaac Ridler Butt. Also available from Amazon: The Tinman's Manual And Builder's And Mechanic's Handbook.
In taking the dimensions of a Cask it must be carefully observed: 1st, That the bung-hole be in the middle of the cask; 2d, That the bung-stave, and the stave opposite to the bung-hole, are both regular and even within; 3d, That the heads of the Cask are equal, and truly circular; if so, the distance between the inside of the chime to the outside of the opposite stave will be the head diameter within the Cask, very near.
If the measure of the Cask is taken outside, with callipers, from head to head, then a deduction must be made of from 1 to 2 inches for the thickness of the heads, according to the size of the Cask.
1 If the staves of the Cask, between the hung and the head, are considerably curved, (the shape of a Pipe), multiply the difference between the bung and head, by .7.
2 If the staves be of a medium curve, (the shape of a Molasses Hogshead), multiply the difference by .65.
3. If the staves curve very little, (less than a Molasses Hogshead), multiply the difference by .6.
4. If the staves are nearly straight, (almost a Cylinder), multiply the difference by .55.
5. Add the product, in each case, to the head-diameter; the sum will be a mean diameter, and thus the Cask is reduced to a cylinder.
6. Multiply the mean diameter by itself, and then by the length, and multiply if for Wine gallons, by .0034. The difference of dividing by 294 (the usual method), and multiplying by .0034 (the most expeditious method), is less than 500ths of a gallon in 100 gallons.
Supposing the Head-Diameter of a Cask to be 24 inches, the Bung-Diameter 32 inches, and the Length of Cask 40 inches; What is the content in Wine Gallons? 1st variety.
carry up Square, 876.16
Ans. 119 galls. 1 pint.
To obtain the contents of a similar Cask in Ale Gallons, multiply 35046.40 by .002785, and we get 97.6042, (or 97 gallons 5 pints.)