| dc.description |
THE following striking experiment to show the rapidity of the influence of sulphuric acid in removing the invisible film of moisture that in ordinary circumstances adheres to the surface of glass and deprives it of its quality as an electric insulator, was recently shown to the Natural Philosophy class in the University of Glasgow by Sir William Thomson, and as it may be interesting to some of your readers, I send you an account of it. The apparatus used were a gold-leaf electroscope, and one of the ordinary table insulators long used in this University, of which the following is a description. A A is a hollow cylinder of brass, the lower part of which can be readily detached, replaced, and fixed in position by a bayonet-joint. The cylinder is supported at the top by the glass rod S, which passes through a circular opening in the bottom of the cylinder and is fixed to the sole plate C. In the lower part is placed a circular canal of lead containing a number of pieces of pumice stone p p, which for insulating purposes are moistened with a few drops of strong sulphuric acid. On the previous evening the pumice pp was moistened with a few drops of water, the cylinder closed and left till morning. The experiment was then performed thus The gold leaves of the electroscope were connected with A A by a fine wire and a charge communicated ; the gold leaves at first repelled each other, but almost immediately collapsed. This was repeated once or twice, to show distinctly that there was no insulation. |
