78 Laboratory Arts 



Moderate pressure only should be used, and wherever 

 possible, the glass should be drilled halfway through from 

 opposite sides, as fracture frequently occurs 

 through the sudden puncture of the second 

 surface, when the drill is apt to press too 

 suddenly upon the sides of the conical 

 hole it is drilling, and so fracture the glass. 

 The drill must be kept moistened with 

 camphorated turpentine, and must be in- 

 FIG. 69. spected from time to time, and ground 



up to sharp edges when necessary upon 

 a fine wet grindstone, or an oilstone. 



Holes through glass tubing may be drilled similarly ; in fact, 

 spectrometer cells are sometimes made from glass tubing 

 about i" diameter, this being ground to the required angle, 

 and two pieces of patent plate cemented in position, a hole 

 drilled in the top of the tube providing the necessary expansion 

 and filling orifice, see Fig. 66. 



"China drills," in the hands of the beginner, appear 

 to be a little heavy, and frequently the glass breaks. The 

 drills should be held as lightly as is consistent with cutting, 

 and with practice it will be found that the drilling of glass 

 is very little more difficult than that of china. In some cases, 

 however, a file sharpened as directed, and twisted between 

 the fingers and thumb, will work its way through the glass 

 quite easily, and be under control to a greater extent than 

 the drill could be, very little pressure being required, and 

 the risk of breaking being therefore much smaller. 



Small cells may be made by taking a piece of plate glass, 

 and grinding it out by means of an emery wheel, moistened 

 with camphorated turpentine, and cementing on each face 

 a piece of patent plate, or even, for rough work, sheet glass 

 such as is used in photographic plates, or microscope slips, see 

 Fig. 64. 



In this case the cement should be the acetic acid-gelatine 

 one. 



Plate glass may be filed into shape for a cell, but it is 

 rather laborious. The file should be constantly moistened 



