ETCHING ON GLASS. 443 



means of the fluoric acid in the state of gas. 

 Having covered over the glass to be etched with 

 a thin coat of virgin-wax (which is only common 

 bees- wax bleached white,) draw the design upon 

 it, in the same manner as in etching on copper. 

 Then take some Jluoy^ spar, commonly called 

 Derhijshire spar, pound it fine, and put it into a 

 leaden vessel, pouring some sulphuric acid over it. 

 Place the glass with the etched side lowermost 

 over this vessel, two or three inches above it^ 

 Apply a gentle heat to the leaden vessel ; this will 

 cause the acid to act upon the fluor spar, and dis- 

 engage the gas, W'hich will corrode the glass. 

 When it is sufficiently corroded, remove the wax 

 by oil of turpentine. 



This etching may be also performed by raising 

 a margin of bordering-wax all round the glass, 

 in the same manner as on copper, and pouring 

 on the liquid fluoric acid, which acts upon the 

 glass. The method of making this acid was 

 described under the article fluoric acid, in che- 

 mistry. 



A third method of etchino; on fflass is as follows : 

 Having put the wax on the glasSj draw your 

 design, and raise a margin all round it. Then 

 ])ut pounded fluor spar, with some sulphuric 

 acid diluted with Vv'ater, upon the glass. The 

 sulphuric acid will disengage the fluoric, which 

 will be absorbed by the water, and corrode the 

 glass. 



In all the above-mentioned methods, some of the 

 gas is let loose in the apartment, and is exceed- 

 ingly suffocating. To remedy this inconvenience, 

 an apparatus was contrived by the editor of this 

 work, some years ago, and is found to answer 

 perfectly. 



