# What fluid weighs 8.32 lbs/gallon?

#### Big O Dave

Maybe I'm off on the wrong track, but as I'm reading oil specs for Castrol Syntec, I'm noticing some kind of linkage between an oil's specific gravity and its pounds per gallon rating. When I divided GC's pounds per gallon rating of 7.05 by its specific gravity of .847, I came up with a pounds per gallon figure of 8.32 for a fluid with a specific gravity of 1.000. I'm just wondering what the reference fluid is that is the 1.000.

#### brianl703

I would think it would be water.

#### bruce381

take specific gravity and multiply by 8.33 (Lbs per gallon of water) Example .847 SG X 8.33 equals 7.05 lbs/per gallon. bruce

#### Matt_S

The definition of specific gravity is the ratio of a substance's density (measured in lbs/gal or g/L) to that of water. That would obviously make water's SG exactly 1.000... ad infinitum. A substance less dense, i.e. lighter, than water would have a SG less than 1. A denser substance would have a SG greater than 1.

#### bulwnkl

quote:
8.33 (Lbs per gallon of water)
What? Do you guys have any idea how badly this screws up the "A pint's a pound the world around" rhyme? What am I supposed to teach my kids now, "A pint's a pound-and-a-24th the world around?" That's just silly! I can't deal with this at all! I say the metric guys used contaminated water for their kilo per litre thing and now everyone's just using that bad reading as the standard!

#### Matt_S

Actually, a kilogram is not defined as the mass of 1 liter of water. It's actually the mass of a reference weight, held in France at the SI headquarters. It's nearly equal to a liter of water, but not exactly, so carry on with your rhyme!

#### XS650

quote:
Originally posted by bulwnkl:
quote:
8.33 (Lbs per gallon of water)
What? Do you guys have any idea how badly this screws up the "A pint's a pound the world around" rhyme? What am I supposed to teach my kids now, "A pint's a pound-and-a-24th the world around?" That's just silly! I can't deal with this at all! I say the metric guys used contaminated water for their kilo per litre thing and now everyone's just using that bad reading as the standard!

Can you work "boiling water" into your little dity? Water is very close to one lb/US Pint at 212F.

#### bulwnkl

Ok, maybe I can work with this. Nobody said at what temp it was 8.33 lbs and nobody said what temp 1 Kilo was 1 Kilo (wait a minute...) so I'm sticking with my rhyme!

#### DriveHard

quote:
Actually, a kilogram is not defined as the mass of 1 liter of water. It's actually the mass of a reference weight, held in France at the SI headquarters. It's nearly equal to a liter of water, but not exactly, so carry on with your rhyme!
I am pretty sure that 1 cc of water weighs exactly 1 gram, and that is what the basis of the measurments are. I will have to do some checking.

#### DriveHard

I guess I used to be right...not anymore. The original unit of mass, the gram, was first defined as the mass of pure water at maximum density that would fill a cube whose edges are each 0.01 m. The unit of mass is now the kilogram, defined as the mass of a platinum-iridium cylinder kept at Sèvres. This is from http://www.maribi.com/conversion/metric_system.asp

#### Matt_S

The definition of the kilogram changed because 1.0L exactly of completely pure water is tough to duplicate. It's also not as precise as it needed to be (water evaporates). Duplicating the mass of a solid reference weight is much easier and more precise. Even now, I understand they're working on a new definition to nail down the mass even more precisely. There would be no reference weight. I don't know much more than that, but one of my college chemistry profs did mention this.