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The standard atmosphere was originally defined as the pressure exerted by a 760 mm column of mercury at 0 °C (32 °F) and standard gravity (g n = 9.806 65 m/s 2). [2] It was used as a reference condition for physical and chemical properties, and the definition of the centigrade temperature scale set 100 °C as the boiling point of water at this pressure.
The tun (Old English: tunne, Latin: tunellus, Middle Latin: tunna) is an English unit of liquid volume (not weight), used for measuring wine, oil or honey. It is typically a large vat or vessel, most often holding 252 wine gallons, but occasionally other sizes (e.g. 256, 240 and 208 gallons) were also used. [1]
A hogshead of brandy was approximately equal to 56–61 gallons (0.255–0.277 m 3). [ citation needed ] Eventually, a hogshead of wine came to be 52.5 imperial gallons (238.669725 L ) (63 US gallons), while a hogshead of beer or ale came to be 54 gallons (249.5421 L with the pre-1824 beer and ale gallon, or 245.48886 L with the imperial gallon).
The Imperial gallon was defined with yet another set of temperature and pressure values (62 °F (17 °C) and 30.0 inHg (102 kPa)). To convert a number of wine gallons to the equivalent number of Imperial gallons, multiply by 0.832674, but to convert a number of Imperial gallons to the equivalent number of wine gallons, multiply by 1.20095.
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth.The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa), which is equivalent to 1,013.25 millibars, [1] 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. [2]
The tun (Old English: tunne, Latin: tunellus, Medieval Latin: tunna) is an English unit of liquid volume (not weight), used for measuring wine, [1] oil or honey. Typically a large vat or vessel, most often holding 252 wine gallons, but occasionally other sizes (e.g. 256, 240 and 208 gallons) were also used. [2]
The pressure is always considered (in brewing) to be 1 standard atmosphere (1,013.25 hPa) and the temperature is usually 20 °C (68 °F) for both sample and water but in some parts of the world different temperatures may be used and there are hydrometers sold calibrated to, for example, 16 °C (60 °F).
The quarter of wine was a gallon larger than a hogshead: [15] since the wine gallon was considered to be 231 cubic inches, [17] the measure was 242.27 litres. The ale gallon was 282 cubic inches, [18] meaning the quarter of ale was 295.75 litres. Cardarelli also says it can vary from 17 to 30 imperial gallons for liquor. [19]