1 HE weights and measures required by the chemift are few and Ample, but they fhould beaccurate, and their relative values well defined.
For the meafure of weight, the Troy pound of 12 ounces, or 5760 grains, is the integeralmoft always preferred, being that which admits of a minuter iubdivifion, and whofe cor-refpondences with meafures of capacity are more accurately defined ; though there are ftill fomeflight differences in this refpect which it were to be wiihed were removed by authority. Thefubdivifions of the Troy ounce employed by chemifls are fometimes t’nofe of Apothecaries weight,that is, the ounce into 8 drams, the dram into 3 fcruples, and the fcruple into 20 grains, or morecommonly, Amply into drams and grains ; or fometimes the ounce is divided into 20 penny-weights, and the pennyweight into 24 grains. Often the grain is the only integer employed,and fets of weights are ufied of the different hundreds, tens, and units. The averdupois poundis however fometimes adopted, being the ftandard of moil things bought and fold in common life.It is equal to 7000 grains J roy, and is divided into 16 ounces, and the ounce legally into 16drams, but the latter divifion is never ufed by chemifls, being liable to be miftaken for the Troydram, which weighs more than tadee as much.
For meafures of capacity, chemills employ both the ounce meafure (or bulk occupied by theounce, or any proportion of it, of difliiled water at 6o°) and the cubic inch. For larger quantitiesboth the Wine Pirrt of 28 875 cubic inches, and the Ale Pint, of 35.25 cubic inches are ufed.Two pints make a Quart, and four quarts make a Gallon.
The correfpondence between meatures of weight and capacity is found by the weight of acubic inch of water. In this however a flight difference exiffs, ir, authorities apparently equallyworthy of confidence, which depends partly on the extreme difficulty of conftructing inftrumentsof perfect accuracy, and partly on fome flight difcrepancy between the ftandards themielves.The extent of this difference is about half a grain in 253. We have adopted in the followingTables the eftimations given by Sir G. Shuckburgh Evelyn, in the 88th vol. of the PhilofoplncalTransactions, corrected in a fubfequent paper by Mr. Fletcher, in the 4th vol. of the Philoio-phical Journal. On this calculation the cubic inch of difliiled water at 6o°. therm, and 29.j bar.weighs 252.506 grains Troy.
Hence we have the following equations.
1 ounce Troy of water at 69 0 occupies1 Wine pint of water weighs - - -
1 Ale Pint of water weighs - - -I lb. Troy of water occupies - - -
I ib. Averdupois of water occupies -
Cubic inch.
- - - -
- 1.900945
grs. Troy.
lb. Troy.
lb. Averdu.
7291.11075
— 1.26581783
=r 1.0415872.
grs. Troy.
lb. Troy.
lb. Averdu.
8900.8365
= i- 545 28 4
= 1.271548
Wine pint.
Ale pint.
. 790003X
= Mr-i 0 ' 1
Wine pint.
Ale pint.
.960073
— .7864429
3 Z 2