Glass Working Cutting, Grinding, and Drilling 75 



to be ground away slightly projecting below the bottom edge 

 of the block. The lower surface of the block must be kept 



FIG. 62. 



FIG. 63. 



perfectly parallel to the emery cloth, during the grinding, which 

 is accomplished by a circular motion. It is not necessary to 

 do one sheet at a time, the whole four, if of equal size, may be 

 ground at once by superimposing over the first plate. 



Having been ground satisfactorily, the edges may be 

 cemented together with any of the cements recommended in 

 Section IV. if only water is to be held, Chatterton's compound, 

 "treacle glue," or "chromate glue," may be used. If only 

 organic liquids are to be used, acetic acid cement is probably 

 the best, though this latter requires fine grinding, and is seen 

 at its best when cementing perfectly smooth or polished sur- 

 faces. When the edges have been smeared with cement they 



j I 



FIG. 64. Lantern cell, made from sheet glass, the actual cell being 

 ground by a wet emery wheel from a piece of plate glass. 



are pressed together, and held in place by a few wrappings with 

 string or fine wire until the cement has fully set. 



