22 



GLASS APPARATUS IN COMMON USE 



have "greasy" surfaces, upon which water gathers in 

 minute drops and effectually prevents the spreading 

 of thin, even films. 



Microscopical Slides. The slides in general use are 

 those known as " three by one" slips (measuring 3 

 inches by i inch, or 76 by 26 mm.), and should be 

 of good white crown glass, with ground edges. 



New slides should be allowed to remain in alcohol 

 acidulated with 5 per cent, hydrochloric acid for some 

 hours, rinsed in running water, roughly drained on a 

 towel, dried, and finally polished with a selvyt cloth. 



FIG. 23. Slides and cover-slips, actual size. 



If only a few slides are required for immediate use 

 a good plan is to rub the surface with jeweler's emery 

 paper (Hubert's oo). A piece of hard wood ;6X26X 

 26 mm. with a piece of this emery paper gummed 

 tightly around it is an exceedingly useful article on 

 the microscope bench. 



Cover=slips. The most useful sizes are the 19 mm. 

 squares for ordinary cover-glass film preparations, and 

 38 by 19 mm. rectangles for blood films and serial sec- 

 tions; both varieties must be of "No. i" thickness, 

 which varies between 0.15 and 0.22 mm., that they 

 may be available for use with the high-power immer- 

 sion lenses. 



Cover-slips should be cleaned in the following man- 

 ner: 



i. Drop the cover-slips one by one into an enamelled 

 iron pot or tall glass beaker, containing a 10 per cent, 

 solution of chromic acid. 



