The Disappearance of the Troy Pound
In 1841 a Royal Commission on Weights and Measures recommended the abolition of the Troy pound as ‘wholly useless,’ retaining its ounce provisionally for the use of bullion merchants, pending ‘the removal of the troy scale.’ This recommendation was not carried out until 1878, when the Troy pound disappeared, except of course in almanacks and books for the instruction of youth—but the Troy ounce still survives at the mint, and consequently in the bullion market; and it is virtually forced on druggists in spite of the Medical Council. Troy weight was abolished by the Pharmacopœia Committee in 1864, Imperial weight being alone recognised; yet the Board of Trade keeps up the Apothecaries’ ounce of 480 grains. Troy weight has fallen; but, like many other superstitions, it dies hard.
CHAPTER X
THE CUBIC FOOT AND THE TON REGISTER
The cubic foot and the cubic inch are the usual measures of solidity. The cubic yard is used as a measure of masonry, earthwork, or reservoirs of water.
The cubic foot has many points of concordance with weights and with measures of capacity, and is the basis of ship and cargo measurement.
The definition of the Imperial gallon as 277·274 cubic inches, the volume of 10 lb. of water at 62°, a pound of water measuring 27·7274 cubic inches, led to attempts to determine accurately the weight of a cubic inch and of a cubic foot of water. These experiments are interesting in consequence of the recognition, in 1685,[[29]] that the cubic foot of water weighed approximately 1000 ounces, and of the probability that this weight of water in Roman ounces, = 437 grains, was the source of our Imperial system. It has already been shown how difficult it is either to construct accurately a measure containing a certain weight of water or conversely to determine the weight of water in a standard measure.[[30]]
The statute definition of the cubic inch of water as = 252·458 grains at 62° corresponds to 62·326 lb., or 997·21 ounces, for the cubic foot. Reduction of these weights to the standard of maximum density of water at 39·2° increases the weight of the cubic inch by 0·29 grain, and of the cubic foot by 1·1 ounce, making it = 62·4 lb. or 998·3 ounces. An Order in Council of 1889 gives 252·286 grains as the weight of the cubic inch of water. But the exact weight is uncertain, and the 1824 statute definition seems to be as accurate as the more recent determinations, all different.
It may be taken that the cubic foot of water weighs very approximately—
| at 62° | in air | 997·2 | ounces | |||
| at 39·2° | in air | 998·3 | „ | (+ 0·9 | ounce | ) |
| at 39·2° | in vacuo | 999·6 | „ | (+ 2·4 | „ | ) |