278 



USE OF THE MICROSCOPE 



A very good artificial light for use with the microscope can 

 be obtained with a Welsbach gas mantle and a balloon flask 

 filled with a light solution of ammoniacal copper sulphate 

 (Fig. 149). Dissolve a very small crystal of copper sulphate 

 in enough water to fill the flask and add ammonia a little at 

 a time until the solution loses all opalescence and becomes 

 perfectly clear blue. Adjust the light and the blue condenser 

 in front of the microscope until an image of the mantle, about 

 natural size, falls on the mirror. Looking through the micro- 



FiG. 149. — Method of illuminating compound microscope with gas lamp. C, Balloon flask- 

 filled with ammonio-sulphate of copper; G. Welsbach mantle. 



scope the light should appear white; if yellow, add more cop- 

 per sulphate; if blue, dilute the solution. This light cannot 

 be excelled and makes one independent of the weather condi- 

 tions or the time of day. 



Drawing to Scale from the Microscope. — There are two 

 ways of drawing from the microscope to a scale that can be 

 accurately determined; one is by the use of an eyepiece mi- 

 crometer, that is, an eyepiece containing a glass disc with a 

 fine scale etched on it. For purposes of drawing, a disc ruled 

 off in very small squares is preferable (Fig. 150). In using 

 this we need to know how large with a given objective an object 

 would be that just fills out the space across one of these squares 



