8 



GLASS APPARATUS IN COMMON USE 



These instruments are expensive and should be reserved 

 solely for standardising the pipettes in ordinary use, and 

 for calibrating small pipettes manufactured in the 

 laboratory. Such a set should comprise, at least, 

 pipettes delivering 10 c.c., 5 c.c., 2.5 c.c., 2 c.c., i c.c., 

 0.5 c.c., 0.25 c.c., 0.2 c.c., o.i c.c., 0.05 c. c., and o.oi c.c., 

 respectively. 



In the immediately following sections are described 

 small' pieces of glass apparatus which should be prepared 

 in the laboratory from glass tubing of various sizes. 

 In their preparation three articles are essential; first 

 a three-square hard-steel file or preferably a glass- work- 

 er's knife of hard Thuringian steel for cutting glass tubes 

 etc. ; next a blowpipe flame, for although much can be 

 done with the ordinary Bunsen burner, a blowpipe 

 flame makes for rapid work; and lastly a bat's- wing 

 burner. 



i . The glass-cutting knife. This article is sold in two 

 forms, a bench knife (Fig. u) and a pocket knife. The 

 former is provided with a blade some 8 cm. in length 



FIG. u. Glass-cutting knife, a. handle, b. double edged blade. 

 c. shaft, d. locking nut. e. spanner for nut. 



and having two cutting edges. The cutting edge when 

 examined in a strong light is seen to be composed of small 

 closely set teeth, similar to those in a saw. The knife 

 should be kept sharp by frequent strappings on a 

 sandstone hone. The pocket form, about 6-cm. long 



