280 



ELEMENTARY CHEMICAL MICROSCOPY 



the latter down at a suitable point. As soon as the proper 

 volume of liquid has been drawn off, still holding the slide 

 inclined, a piece of filter or folded lens paper is drawn through the 

 channel, between the two drops at C, Fig. 146, and the prepara- 

 tion immediately heated gently over the micro-flame at this 

 same point. The result of this heating is the separation of the 

 two drops by a dry space ; thus there is no danger of the decanted 

 liquid flowing back when the slide is again placed in a horizontal 

 position. 



Eig. 146. Decanting a Drop of Liquid from a Precipitate. 



When the clear decanted liquid is not wanted for analysis and 

 only the sediment, or precipitate, in the original drop is to be 

 utilized, the decanted portion and connecting stream are both 

 wiped off the slide with filter paper while the slide is inclined and 

 the preparation heated gently below the wiped-off drop to pre- 

 vent any farther spreading. 



In cases where the sediment in the drop persists in flowing with 

 the liquid being drawn off, and where heating is not objection- 

 able, the slide is tipped so as to cause all the liquid to again flow 

 back into the original source and the drop is evaporated to dry- 

 ness at a low temperature, exceptional care being taken to pre- 

 vent heating the residue after evaporation. This step will 

 usually cause the sediment to cling to the glass and to aggluti- 

 nate. A drop of water or the proper liquid is then carefully 

 added, the preparation allowed to stand a few seconds to permit 

 the soluble compounds to pass into solution and the solution 

 then decanted as above described. Usually a clear liquid may 

 now be obtained without difficulty. 



