THE METHODS OF MICROCHEMICAL QUALITATIVE ANALYSIS 315 



In a similar manner traces of moisture (or water of hydration 

 in tiny crystals) can easily be recognized by placing a minute 

 quantity of dry powdered fuchsine in a capillary tube and causing 

 the moist air to pass over it by heating. The change from the 

 greenish black powder to crimson droplets is very striking. 



Numerous other examples might be given. 



EXPERIMENTS. 



a. Place in the crucible of the apparatus, Fig. 153, two or three fibers of 

 asbestos, drop upon them a single drop of bromine (in the hood). Invert over 

 the crucible a drop of a solution of a sulphide. Lower the clamp and warm 

 gently in the hood, until the crucible is filled with bromine vapors. Allow to stand 

 for about five minutes. During this period test a portion of the unoxidized ma- 

 terial for sulphates as below. Lift off the object slide from the crucible, turn it 

 drop side up and evaporate to dryness; add a drop of water to the cool residue, 

 then a tiny drop of HN0 3 . Decant if not clear, and finally test for sulphates by 

 adding a drop of Ca(C 2 H 3 2 )2- (Method /.) CaS0 4 • 2H2O separates in the form 

 of radiating tufts or X's of monoclinic needles or thin prisms. 



b. Place in the glass crucible a dilute solution of KCN. Cover it with an 

 object slide, carrying a small drop of AgN0 3 upon its under side. Raise the slide 

 just enough to permit dropping in several small grains of primary sodium car- 

 bonate (HNaC0 3 ). Cover tightly at once and allow to stand for five or ten 

 minutes. If, after this interval, no cloudiness is visible, warm the crucible gently. 

 Remove the slide and examine it with a \ inch or 8 millimeter objective. AgCN 

 appears as small colorless prisms with obliquely truncated ends. 



XIV. Methods involving fusing the material in a bead of borax, 

 microcosmic salt or other medium. 



Some of the very earliest attempts to employ the microscope 

 for the detection of minute amounts of material were made in 

 conjunction with the blowpipe analysis of minerals. It was 

 found that many substances yielded characteristic crystals 

 when fused in borax beads before the blowpipe at high tem- 

 peratures. 



Although of questionable usefulness in systematic analysis, 

 this method is of sufficient interest to the student to be well 

 worthy of trial and study. 1 



To obtain a loop wind a platinum wire twice around a glass 



1 See Sorby, Chem. News, 19 (1869), 124; Wunder, J. f. prak. Chem., 109 

 (1870), 452; Emerson, Proc. Amer. Acad. Arts and Sci., 6, 476. 



