Hydrometer Scales

Close examination of these equations, shows that accurate calibration of the hydrometer with several different liquids allows a precise graduation of the immersed height directly in specific gravity units, or hydrometer scales (e.g., Baum, Twaddell, API, etc.). 

For more hydrometer scales see Cardarelli, F. (2005) Encyclopaedia of Scientific Units, Weights and Measures. Their SI equivalences and Origins. Springer, New York, 872 pages 

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In the most commonly used method (ASTM D1298 IP 160), the sample is brought to the prescribed temperature and transferred to a cylinder at approximately the same temperature. The appropriate hydrometer is lowered into the sample and allowed to settle, and after temperature equilibrium has been reached, the hydrometer scale is read and the temperature of the sample is noted. 

Baume hydrometer scale phys chem A calibration scale for liquids that is reducible to specific gravity by the following formulas for liquids heavier than water, specific gravity = H5 a- — n) at 60°F for liquids lighter than water, specific gravity = 140 a- (130 + n) at 60°F n is the reading on the Baume scale, in degrees Baume Baume is abbreviated Be. bo ma hT dram-ad-ar, skal )... 

Antoine Baum , 1728-1804. French pharmacist and chemist. Author of a Chymie expenmentale et raisonnee in which he discussed chemical apparatus, chemical affinity, fire, air, earth, water, sulfur, gypsum, alum, clay, niter, gunpowder, borax, arsenic, glass, porcelain, and the common acids, alkalies, metals, and ores used m 1773. His hydrometer scale is still used. He was one of the first chemists to investigate platinum... 

In the petroleum industry the specific gravity of petroleum products is usually reported in terms of a hydrometer scale called °API. The equation for the API scale is... 

The API gravity (ASTM D-287, IP 192) is also used for lubricating oil and is based on a hydrometer scale that may be readily converted to a relative density basis by use of tables or formulae (Chapter 2) ... 

In tho Tralles hydrometer scale there is no reference to proof of any denomination aud... 

Table 20.1. Hydrometer scales Scale Liquids heavier than water...

When the hydrometer has come to rest, floating freely away from the wiUls of the cylinder (Note 4), estimate the hydrometer scale reading to the nearest 0.(XX)1 relative... 

Immediately after observing the hydrometer scale value, again cautiously stir the sample with the thermometer keeping the mercury thread fully immersed. Record the temperature of the sample to the nearest 0.2 C (O.S F) (Note 6). Should this temperature differ from the previous reading by more than 0.5 C (1 F), repeat the hydrometer test and then thermometer observations until the temperature becomes stable within O.S C (1 F). 

Note 7—Hydrometer scale readings at temperatures other than calibration temperatures (1S C or 60 F) should not be considered as more than scale readings since the hydrometer bulb changes with temperature. 

When a value is obtained with a hydrometer scaled in one of the units described herein and a result is requited in... 

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