OF MICROSCOPIC OBJECTS. 25 



should, therefore, he taken to sort them, so that the more 

 pelicate ohjects with which the higher powers are to be 

 used may be mounted upon the thinnest, as the light em- 

 ployed in the illumination is then less interfered with. To 

 aid the microscopist in this work, a metal circle may be pro- 

 cured, having a number of different sized openings on the 

 outer edge, by which glass slides can be measured. These 

 openings are numbered, and the slides may be separated 

 according to these numbers; so that when mounting any 

 object there will be no need of a long search for that glass 

 which is best suited to it. 



When fresh from the dealer's hands, these slides are 

 generally covered with dust, &c., which may be removed by 

 well washing in clean rain-water ; but if the impurity is 

 obstinate, a little washing soda may be added, care being 

 taken, however, that every trace of this is removed by sub- 

 sequent waters, otherwise, crystals will afterwards form upon 

 the surface. Sometimes, however, a certain greasiiiess is 

 very obstinate upon the glass. It is then necessary to use 

 a little liquor potassse with a small piece of linen, rubbing 

 the slide with some pressure, and then washing as before to 

 remove all remains. A clean linen cloth should be used to 

 dry the slides, after which they may be laid by for use. 

 Immediately, however, before being used for the reception of 

 objects by any of the following processes, all dust must be 

 removed by rubbing the surface with clean wash-leather or 

 a piece of cambric, and, if needful, breathing upon it, and 

 then using the leather or camhric until perfectly dry. Any 

 small particles left upon the surface may generally be 

 removed by blowing gently upon it, taking care to allow no 

 damp to remain. A very efficient remedy, also, is a mixture 

 of equal parts of sulphuric ether and alcohol, with which 

 the glass must be rubbed by the aid of a tuft of clean 

 cotton-wool until no stain appears after breathing upon it. 

 A strong infusion of nutgalls may be used in the same way, 

 and is preferred by many to all other applications; or, a 

 mixture of equal parts of alcohol, bea^ole, and liquor sodse 



