Fig. 95. etching glass with acid
A. Etching a sheet of glass with fluor-spar.
B. Etching a thermometer tube with hydrofluoric acid.
The next morning when you take off the glass, scrape off the wax and you will find the name or design etched on it.
To etch the graduations on thermometers, burettes, etc., coat them with wax and scratch the lines and figures on them just as described above—but in this case you can put the hydrofluoric acid on direct as shown at [B], using a splinter of wood for the purpose.
How to Cement Glass.
—To cement glass clean the edges or surfaces to be fixed together with hot water in which you have put a little soda; dry well with a clean cloth and then be careful not to let your fingers touch the cleaned parts.
Brush over the edges or surfaces of the glass with the cement made according to the directions which follow and press and bind the parts together as tightly as possible.
To make the cement dissolve 2 ounces of the best gum arabic in some hot water and then add 1¹⁄₂ ounces of pulverized starch and ¹⁄₂ ounce of sugar and stir until they are dissolved. Heat the mixture in a pot or a tin can which sets in a larger pot or tin of water—or water bath as it is called.
When the starch gets clear take it from the fire, put in a few drops of oil of cloves to keep the cement sweet and let it get cold, when it should be about as thick as cream.