API system of density measurement - WHY?

[DynamoDiabolo]

Does anyone know the reason behind the API system of density measurement? I though it might be because it's additive for if two oils are being mixed together, but does anyone know for sure?

 

[jsummerfield]

The way that you speak of density, I gather that you are addressing the API gravity measurements with increasing numbers for lighter densities, correct?

John

 

[Guidoo]

Is this what you are looking for? Following was copied from

http://www.chevron.com:

"The United States petroleum industry often uses API gravity instead of relative density. The following equation relates API gravity, in degrees API (°API), to relative density.

141.5
°API = ––––––––––––- – 131.5
RD (60 / 60°F)


While API gravity measurements may be made on liquids at temperatures other than 60°F, the results are always converted to the values at 60°F, the standard temperature.
API gravity is an arbitrary scale developed by the American Petroleum Institute in the early years of the petroleum industry. Density had been used as a primary indicator of quality for liquid products. However the higher value products have lower densities. The API gravity scale was constructed so that API gravity increases inversely to density; therefore, higher value products have higher API gravities. And while the densities of most petroleum products are less than one, the API gravity scale also was constructed so that most values are between 10 and 70."