126 ELEMENTARY CHEMICAL MICROSCOPY 



Watch Glasses. When volumes of liquid greater than can 

 be handled upon object slides become necessary, small watch 

 glasses 10 millimeters and 25 millimeters in diameter will be found 

 convenient. Only the deep type of watch glass should be 

 employed; for example, a 25 millimeter watch glass should be 

 from 3 to 5 millimeters deep. Instead of 10 millimeter shallow 

 watch glasses, object slides with a depression ground into them 

 will be found better and more convenient. 



Watch glasses are useful for covering preparations, for making 

 tiny moist chambers, for microdesiccators, for distilling and 

 subliming, and for evaporating solutions to small bulk. 



Most small watch glasses are made 

 from soft non-resistant glass, a fact 

 which should be borne in mind when 

 using them. 



Still larger volumes of liquid than 

 can be accommodated in small watch 

 glasses are best concentrated in small 

 FIG. 71. Best Form of Glass evaporators of transparent quartz or 



or Quartz Evaporator for T , /T ^. N Tr ,, vi. .a 4. 



Microchemical Work. J ena S lasS ( Fl - ?') those With flat 



bottoms are chosen they may be placed 



upon the stage of the microscope and any crystals, deposits, etc., 

 examined with low powers as well as if the material were trans- 

 ferred to a glass object slide. 



Gas Lamps for Microchemical Work. The form of " mi- 

 crochemical burner" commonly referred to in the older manuals 

 on the microscope and microscopic methods is shown in Fig. 

 72. This burner answers admirably for all purposes involving 

 only moderate heating of very small amounts of material. 

 Since, however, microchemical methods often require a prelimi- 

 nary handling of several grams or cubic centimeters of substance, 

 the burner shown in Fig. 73 will be found to afford a wider range 

 of usefulness. It also occupies less space upon the work table. 

 It consists of an ordinary Bunsen burner provided with a side 

 tube for a " reserve" or " pilot" flame. In the form illustrated, 

 the tiny flame B (reserve flame) employed for microchemical 

 work is furnished by a small brass tube inside the Bunsen tube. 



