Medical Normal Saline (0.9% Saline) contains 9 g of salt dissolved in 1000ml of water.
Hence a litre of NS should weigh 1.009 kg.
Hence its specific gravity should be 1.009, but it’s only 1.0046. (I've measured it, and verified it on-line. It is apparently, a fact.) I thought I understood SG, it’s a simple concept but I am missing something.
EDIT: after more reading, I learned that dissolving NaCl in water results in a reduction in the original volume. So my question now becomes: We're dissolving NaCl in pure water at a temperature where 1.000kg mass of water has a volume of 1.000 litres. By my (erroneous) reasoning: Say the volume decreases by 1 ml, giving a final volume of 0.999 litres. So the density of the solution would be 1.009 kg/ 0.999 l = 1.010 kg/l Giving an SG of 1.010 (because water has a density of 1.000 kg/l, as above) If the volume didn't change, it would be 1.009, but it increases because of the reduction in volume. BUT: The known, published SG of 0.9% w/v NaCl solution is 1.0046. Can anyone explain why, please? or at least, why the SG is below 1.009, when it should be greater?