HANDLING SMALL AMOUNTS OF MATERIAL: SOLUBILITY 277 



necessary to remember that directions are reversed in the image 

 formed by the microscope and seen by the worker, but if this is 

 borne in mind there will soon be no difficulty in moving and 

 turning objects while observing them through the microscope. 



If, after a few minutes, there appears to be no change in the 

 appearance or size of the material being tested, warm the drop 

 gently by holding it a second or two about one centimeter above 

 the " reserve " or " pilot " flame of the laboratory burner (see 

 Fig. 87, page 153). This tiny flame should be so regulated by 

 means of the set screw as not to be over 5 millimeters high. Cool 

 the preparation quickly by holding the slip for an instant in con- 

 tact with a smooth metal block placed for this purpose near the 

 burner, or, in the absence of such a cooling device, place the slide 

 on the base of the microscope. Examine the fragment of material 

 to be tested and note any change in its appearance and size. 



To heat a solution to boiling have a large drop at the very 

 corner of a glass slip, tip the slip slightly so that the drop flows 

 toward the corner and hold it so that the tip of the micro- 

 flame (pilot flame) touches the glass just below the upper edge 

 of the inclined drop. Watch closely and as soon as bubbles rise, 

 remove from the flame and cool instantly by bringing in contact 

 with a cool metal surface. It is necessary to work quickly, 

 otherwise the evaporation will be so great that the preparation 

 will become dry. Never place' a hot slide on the stage of the mi- 

 croscope, for the stage may be seriously damaged and the vapors 

 arising will condense upon the objectives injuring them. Since 

 the drop has been placed at the corner of the slide there is no 

 danger of the glass cracking or breaking on heating, an accident 

 that will almost invariably happen if the glass slip is heated at 

 any other point than a corner. If quartz or platinum slips are 

 used, heating at the corner is not essential to prevent breakage, 

 but is more convenient. 



To determine whether any material has passed into solution, 

 decant the liquid from the undissolved material (see Decanting 

 below), and evaporate to dryness very carefully. In evapora- 

 ting drops to dryness, never keep the material over the flame 

 until all the liquid has been driven off. Simply warm the prepa- 



