I don't understand what you're saying about the difference in specific gravity between non iodized table salt (read that "common aquarium salt") and sea salt. By weight, sea salt and table salt contain about the same amount of sodium chloride, nitrogen chlorine or NaCl whichever you prefer.
A refract is not measuring Sg or Salinity. It is measuring the RI (Refractive Index) of the water. That RI is then converted to a Sg or Salinity based on a NaCl or Seawater scale by that RI conversion.
By weight, sea salt and table salt contain about the same amount of sodium chloride, nitrogen chlorine or NaCl whichever you prefer.
No, table salt is almost pure NaCl @ 35 ppt NaCl. It is half of each and NaCl makes up 30 ppt of seawater
You need to read this. It takes 37.4 grams of NaCl to equal 35 grams of 100 % dehydrated NSW to get a NSW salinity of 35 ppt@ 20 C 1 atm
Reef Aquarium Salinity: Homemade Calibration Standards
http://www.reefkeeping.com/issues/2004-06/rhf/index.php
In regard to your question about "Why do research labs have refractometers with automatic compensation for shifts in ambient temperature?" It's nothing to do with the change in refractive index of aqueous solutions.
Yes it does. At lower water temps the RI is changed due to density. D is higher at lower temp, and lower at warmed temp and D changes R.I The ATC thus allows one not have to worry about temp variations within reason. Non- ATC refracts MUST be calibrated at calibrated temp and the sample test water needs to be at that temp unless you have temp correction tables.
I trust steam distilled water (DH20) for calibrating my 33.3 ppt seawater refractometer because it brings the refractometer to zero and costs 58 cents per gallon.
You can't unless it is real lab grade refract. Many of these cheap Chinese refracts have issues with optical quality of the glass. In RO/DI or Tri-D water they can be off as much as 4 ppt. A real lab grade 1.5 ppt off.
You posted this;
http://reefkeeping.com/issues/2006-12/rhf/index.php
Did you read it ? I helped write it
We are not talking about natural seawater; we're talking about aquarium water which tends to get too warm or too cold or have anything else go wrong when we're not looking. I’ll be ready to discuss establishing the conditions of natural seawater when somebody has an aquarium with cubic miles of capacity.
I don't need lessons. I have been testing and studying it for 40 years. Do you know what NSW conditions are ?
Salinity is what the livestock in an aquarium react to and the parts-per-thousand of salt in the water is only one component of salinity.
You have a total misunderstanding what salinity is. Rather than me explain it just read this.
What is Salinity
http://reefkeeping.com/issues/2005-11/rhf/index.php
Also we're only talking about using either non-iodized table salt or not so heavily processed sea salt, not two different species of salts. It's the same salt, all of it, NaCl.
ASW is pretty close to NSW and has about the same NaCl ~ 30 ppt of 35 ppt.
Do you know what a salt is chemically ? NaCl, KCl, CaSO4, MgSO4, CaCO3, MgCl MgSO4, etc, etc are all salts. It is when an Cation like Ca++ attaches to a Anion like CO3-- by a Ionic bound = CaCO3 or Ca:CO3, where " : " equals the ionic bond, a positive and negative attraction like iron to a magnet.
"mock sea water"
It is a salt mix which does not have to be the same as NSW that still yields the same Sg, RI, conductivity and Salinity of NSW.
You have a very poor understanding of seawater chemistry. You may want to look at the sticky's I have posted here on the RF Chemistry forum that I moderate.
Reef Chemistry Discussion with Boomer
http://www.reeffrontiers.com/forums/forumdisplay.php?f=72