Thursday, June 26, 2008

Specific Gravity is a measure of the density of a liquid relative to water. Specific gravity measurements are essential to many industries. Wine makers use specific gravity to monitor the fermentation process. These measurements would be taken with a refractometer or hydrometer and be in units of degrees Brix or Baume (Be). Brewers also use refractometers and hydrometers to monitor the change in sugar content of the fermenting wort. Sugar is not the only dissolved solid that is measured by specific gravity. Salt content or salinity is also measured this way. If you have a salt water fish tank at home you probably use a refractometer to determine the saline level. A refractometer measures refractive index. Refractive index is a measure of the speed of light through a substance relative to the speed of light in air. When water has dissolved solids such as salt or sugar this changes the refractive index. Both refractive index and specific gravity are dependent on the temperature of the sample. Specific gravity is also important in the petroleum industry. The petroleum industry uses API gravity (American Petroleum Institute) and ASTM Hydrometers to measure the density of crude oil and petroleum products. HB Instrument Co. manufactures Specific Gravity, Brix , Baume, and API Hydrometers. Kessler produces Baume (Be) hydrometer/thermometers and Nalge Nunc produces polycarbonate salt and specific gravity hydrometers. Reichert and Mettler Toledo are manufacturers of refractometers. So the next time you bid $150.00/barrel on that 1,000,000 barrels of sweet light crude, be sure you have your API hydrometer handy to check the quality.