10 ELEMENTARY CHEMICAL MICROSCOPY 



When abrasives are employed (as, for example, in metallo- 

 graphic work) even in adjoining rooms, all lenses should first be 

 blown upon (but not breathed upon) and then dusted off with 

 a very soft camel's hair brush before wiping with lens paper, 

 otherwise serious scratching of the glass will sooner or later result. 



Dust on the back lens combination of the objective is often 

 responsible for great loss of definition and greatly reduces the 

 resolving power of an objective. Dust on the rear lens may 

 easily be seen by removing the ocular, illuminating the objec- 

 tive to its full capacity and looking into the microscope tube. 

 Often a screen of ground glass placed in front of the microscope 

 mirror renders the dust particles more clearly discernible. 



After using an immersion objective immediately wipe off the 

 immersion fluid with lens paper, then if the fluid is oil, wipe the 

 lens with lens paper moistened with xylene, and finally wipe 

 dry. Never use alcohol in cleaning objectives or any part of 

 the microscope. Never allow an objective to remain moistened 

 with any fluid whatsoever a moment longer than absolutely 

 necessary. 



When focusing a microscope upon a preparation, first turn the 

 body tube down by means of the coarse adjustment until the 

 objective is closer to the preparation than is indicated by 

 the equivalent focus of the objective, watching carefully with 

 the head to one side to see that the front lens is not forced 

 against the slide. Look into the microscope and slowly raise 

 the tube by the coarse adjustment until the object is almost 

 in focus; complete the adjustment by means of the fine adjust- 

 ment. Never focus down while looking into the instrument. 

 Failure to observe this simple rule is apt to lead to serious loss 

 and considerable expense. 



Never change from one objective to another without first 

 making sure that the body tube has been raised sufficiently to 

 allow the new objective to be slipped into place without injury 

 to the preparation on the stage or to the objective. 



Never handle objectives or oculars or, in fact, any parts of 

 the microscope with dirty, greasy, or wet fingers, or when the 

 hands are so cold as to incur danger of dropping the apparatus. 



