| 摘要 |
<p>Motor cars can be secured against theft by etching in the corners of each window the car registration number or other identity letters. This is done by applying a stamp, soaked in hydrofluoric acid. The stamp is pref. made of porous balsa wood to which the acid is applied by a pad. The acid is attracted by the osmosis effect into the wood and is transferred to the glass panes in sharp outlines. Stamps give a cleaner impression than rubber stamps and can be produced at lower cost.</p> |
