Volume 74 Item 09: Sir William Macarthur collection of pamphlets relating to viticulture, 1828-1880: No. 010
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The infusion of malt, which is called Wort, is heavier than water according to the quantity of saccharine matter which it holds in solution; the weight or gravity of Wort is therefore a criterion of its value, which, besides being determinable with the greatest ease and expedition, is always sufficiently accurate for the purposes of Commerce or Revenue.
The term Gravity has been by some applied to Worts, as expressive of their excess or difference of weight above the weight of Water; by others, to express the weight of saccharine matter in a Barrel of them; and again by other, to express the excess in their weight above that of an equal bulk of Water in one thousandth parts of the weight of the latter, and these parts are called "Degrees of Gravity"; they are, however, only correctly so when they refer to the weight of pure Water at a fixed heat or Temperature, and these comparative weights of equal measures are then Specific Gravities.
The Specific Gravity of Wort may be obtained, like that of any other liquid, from the weight which a solid body loses by immersion in it, compared with the weight which the solid loses in Water, and is the quotient of the weight lost in the Wort, divided by the weight lost in the Water. The Specific Gravity of liquids is also ascertained by successively filling a small vessel to the same height, and weighing the contents; this vessel is called the Weighing-bottle: but these methods, each requiring the employment of a good Balance, are too tardy and expensive for general adoption.
An Instrument, the reverse of the Weighing-bottle, was therefore introduced, which being made to float at a given point in Water, was, by the addition of Weights at the top of it, made to sink to the same depth in other liquids, and thus always displaced an equal bulk or measure of liquid: this Instrument is named a Gravimeter; and when its weight in Water is called Unity (the accompanying Weights being