84: CHEMICAL PROPERTIES OF MINERALS. 



To ascertain the fusibility of a mineral, the fragment for the 

 platinum forceps should not be larger than the head of a pin, 

 and, if possible, should be tbin and oblong, so "that the extrem- 

 ity may project beyond the platinum. The fusible metals alloy 

 readily with platinum. Hence compounds of lead, arsenic, an- 

 timony, etc., must be guarded against. These compounds are 

 tested on charcoal. The forceps should not be used with the 

 iuxes, but instead either charcoal or the platinum wire or foil. 



The charcoal should be firm and well burnt ; that of soft 

 wood is the best. It is employed especially for the reduction 

 of oxides, in which the presence of carbon is often necessary, 

 and also for observing any substances which may pass off and 

 be deposited on the charcoal around the assay. These coatings 

 are usually oxides of the metals, which are formed by the oxi- 

 dation of the volatile metals as they issue from the reduction 

 flame. 



The platinum wire is employed in order to observe the ac- 

 tion of the fluxes on the mineral, and the colors which the 

 oxides impart to the fluxes when dissolved in them. The wire 

 used is No. 27. This is cut into pieces about three inches long, 

 and the end is bent into a small loop, in which the flux is fused. 

 This makes what is called a bead. When the experiment is 

 complete the beads are removed by uncoiling the loop and draw- 

 ing the wire through the finger nails. After use for awhile the 

 end breaks off, because platinum is acted upon by the soda, and 

 then a new loop has to be made. Dilute sulphuric acid will 

 remove any of the flux that may remain upon it after a trial 

 has been made. 



Glass tube is employed for various purposes. It should be 

 from a line to a fourth of an inch in bore. It is cut into pieces 

 four to six inches long, and used in some cases with both ends 

 open, in others with one end closed. In the closed tube, either 

 heated directly over the Bunsen burner, or with the aid of the 

 blowpipe, volatile substances in the assay are vaporized and 

 condensed in the upper colder part of the tube, where they 

 may be examined by a lens if necessary, or by further heating. 

 The odor given off may also be noted, and the acidity of any 

 fumes bj inserting a small strip of litmus paper in the mouth 

 of the tube. The closed tube is used to observe all the effects 

 that may take place when a substance is heated out of contact 

 with the air. In the open tube the atmosphere passes through 

 the tube in the heating, and so modifies the result. The assay 

 is placed an inch or an iuch and a quarter from the lower end 

 of the tube ; the tube should be held nearly horizontally, to 



