1894.] MICROSCOPICAL JOURNAL. 347 



of color as though they were partially discolored, so that 

 it makes a much brighter slide when mounted in castor- 

 oil. In mounting, let the first drop of oil run to waste, 

 and drop sufficient oil on to well cover the preparation. 

 As the crystals are far from flat, it will take several 

 drops of the oil to fill the space occupied by the cover- 

 glass. Before covering with the glass, put the prepa- 

 ration away for a day under a bell-glass to allow the air- 

 bubbles to escape ; and, before mounting look at the 

 slide under the microscope to make sure that is worth 

 being completed. 



When you have some thickness of oil contained between 

 the slide and the cover, it is necessary to be very careful 

 not to remove any of the oil by the brush in cleaning the 

 edges. A good plan is to tack one side with a small 

 drop of lac-varnish, and let it dry before proceeding to 

 ring the slide. The cover resting on the tops of the 

 crystals is almost sure to be displaced by the brush, 

 when you try to trim a ring on the turn-table without 

 this precaution. By getting a small spot on one side and 

 drying it, it gives a sufiicient hold to the cover to pre- 

 vent it slipping under the pressure of the varnish brush. 

 This can also be effected by putting a small conical pis- 

 tol bullet on the glass co\^er after it is centered on the 

 turn-table, the weight preventing the cover being shifted 

 by the brush. 



This makes a very good slide and nearly every one 

 will crystallize uniformly and with well-defined and clear 

 crystals. The crystals are much better if allowed to dry 

 spontaneously than if dried ofi" on the hot-plate; although, 

 of course, the size of the crystals vary according to the 

 heat of weather in which the slide is prepared, in cold 

 weather the crystals being larger. 



OXALATE OF CHROMIUM AND POTASH. 



This salt gives a very brilliant slide and is also di- 



