Sodium Thiosulphate is a standard and universal fixing agent. Anhydrous means that all water has been removed from the chemical unlike the "penta" version with 33% water in it and is often referred to as Hypo.
Here are our basic fixer formula for making a basic paper fixier
F-24 ACID FIXER FOR PAPER
Water (100-125º F)…………..………… 750ml ………. 1500 ………. 3000 …………. 6000
Sodium Thiosulfate Anhydrous 152 g 304 g 608 g 1216 g
Sodium Sulfite ………………..……….. 10 g …………. 20 g ……….. 40 g .……….… 80 g
Sodium Metabisulfhate ………….….……….. 25 g ………….. 50 g ……….. 100 g ……..…. 200 g
Water to make ………………..………. 1 Ltr ………….. 2 Ltr ………. 4 Ltr …………. 8 Ltr
Never make your water over 27 degrees in this formula.
Mix in the order shown and use undiluted. Fix paper for 4 minutes. Wash prints in running water for 5-10 minutes.
The molecular formula is: Na2S2O3.xH2O