and then 5 10 ml of sterile water added until the opalescense in the solution disappears a yellow gum is produced and sticks to the bottom and sides of the tube the colourless solution is decanted off and evaporated to dryness under vacuum the yellow gum can also be solidified by drying under vacuum the product from the colourless solution is stable to heat and light and non toxic to platelets the solidified yellow gum which gives a very pale yellow solid is sensitive to heat and light and is toxic to platelets differences were found in the spectral absorption patterns of the colourless and yellow forms of sodium aurothiomalate see fig1 as measured in aqueous solutions in 1 cm cells with use of a pye unicam sp8 100 trademark spectrophotometer not only were differences found in the visible spectrum fig1 a but there were also demonstrable differences in the ultraviolet range fig1 b differences were also found in platelet toxicity as measured by the relative ability of the compounds to cause platelet aggregation see fig2 the procedure employed to obtain platelets was as follows 129 ml of blood was obtained by antecubital vein puncture from volunteers volunteers were selected who were on no medications and had taken no medication for two weeks the blood was immediately transferred in equal volumes to 3 plastic centrifuge tubes 5 ml each containing 7 ml of acid citrate dextrose acd anticoagulant solution the whole blood acd mixture was gently but rapidly mixed to prevent clotting the suspension was then centrifuged at 37 u00b0.