﻿IX, B, 4 Barber: The Pipette Method 317 



capillary. With a little experience, one can usually tell when a 

 proper point is made by the peculiar feeling described above, but, 

 if desired, the point may be inspected under the low power of 

 the microscope or with a good hand lens. If too little heat is 

 used and the pull made too suddenly, the capillary may part 

 with a snap and the tip may have an opening too large for use. 

 However, if a capillary parts with a snap and is seen to end 

 in a very fine point, it is well to turn up the tip (see paragraph 

 e) and place the pipette in the holder for inspection under 

 the microscope. Sometimes excellent pipettes, with a small 

 polished opening, are obtained when the glass, in a half-molten 

 condition, parts with a gentle snap, c (fig. 6). 



Fig. 6. a. Completed pipette ; h, c, and d, various sorts of points. 



If too much heat is used, the capillary is apt to be drawn 

 into a long, hair-like ending, d (fig. 6). This is especially apt 

 to be the case when the capillary is pulled with the right hand 

 instead of with the forceps. Such points may be made service- 

 able by clipping off the end with sterile scissors or forceps or by 

 placing the end on a slide and cutting off a portion with a scalpel. 

 For the best work, however, the form b (fig. 6) will be found 

 preferable to the others. 



If the learner has continued difficulty in obtaining a suitable 

 point, it is well to try hard glass. The capillaries are drawn 

 out in the blast flame, and may be made of slightly varying 

 diameters. The flame of the microburner should be slightly 

 higher than for soft glass. A number of capillaries may be 



