------------------------------------------------------------------------
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]
‘Some Gentlemen at Oxford in 1685 determined the weight of a cubic foot of spring water, or 1728 solid inches, to be 1000 ounces averdepois.’—Kelly, _Metrology_, 1816.
For this reason the custodians of the metric system have abandoned the cubic decimetre of water as the basis of measures either of capacity or of weight. The kilogramme is now, like our pound, a certain metal standard, and the litre is a measure containing, more or less exactly, a kilogramme of water. A perfect litre standard contains 1000 grammes of water at 39·2°; but 1·1 gramme less at 62°, 2 grammes less at 70°, and 3·3 grammes less at 80°, a very frequent summer temperature. For exact correspondence of measure with weight, corrections are always required whether on the imperial or on the metric system.
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.