1. They are described somewhere in the handbook.

2. What values do they take - 4, 17, 20, 22, 25? If so, these are deg C temperatures. I don't remember details about why there are two sometimes - probably it means that the density was measured compared to the water density and one temp. is for substance, and the second is for water. But I can be wrong.

the problem with that, however, is that sometimes there are not two numbers present, and density is always the same.

They are probably given only if known.

temperature will not change how dense something is

Huh? Water is 0.99913 at 15 deg C and 0.99823 at 20 deg C. Is this 'no change'?

and also, the meaning of the numbers is not present in the explanation of abbreviations in the pretext charts    but thank you so much!!!!!

Check earlier sections - it is probably described before the symbol is used for the first time in whole handbook (perhaps before inorganic section? or some general section about raw materials - I don't have CRC handbook so I can't check, but that's how such handbooks are constructed).

and i'm in chemistry class right now --ps by the way--

thanks!!! --just quoting what my chem teacher says-- maybe we aren't that far!!! --take a chil pill!!!! especially since you're wrong!!! density does not change ok bye

Blasphemy..

Example: water - fill a plastic bottle to the top with water, screw the cap on and put it in the freezer. Wait overnight and see what happens.

That will be phase transition, not volume change due to temperature change.

Whatever you call it - it is volume change due to temperature change..