Metal particles in ophthalmic ointments
1. Melt the contents of 10 tubes individually/separately in 60mm petri dishes
2. Cover the dishes and heat at 85 degree celcius for 2 hours; if needed slightly increase the temperature to achieve full fluidity
3. Allow each to cool at room temperature and solidify
4. Invert the Petri dish on the stage of microscope furnishing 30 times magnification and equipped with calibrate eye piece micrometer
5. In addition to usual light source, direct an illuminator from the above at an angle of 45 degree
6. Examine the bottom of the entire Petri dish for metal particles