Amazon.com description: Product Description: The face of the man sitting at the table watching this unsavory stew was hidden behind a mica and rubber mask, for the fumes which were being given off by the fluid were neither pleasant nor healthy. Save for a shaded light upon the table and the blue glow of the Bunsen lamp, the room was in darkness. Now and again the student would take a glass rod, dip it for an instant into the boiling liquid, and, lifting it, would allow the liquid drop by drop to fall from the rod on to a strip of litmus paper. What he saw was evidently satisfactory, and presently he turned out the Bunsen lamp, walked to the window and opened it, and switched on an electric fan to aid the process of ventilation.