l\>li;i MI. NTS AM) CHEMICAL Tl.STS. 557 



solution ha- drained otV, tin- solid- are \\a-lnd l.y dropping distilled 

 \\ater from the \v;i.-h bottle :iroimd the edire of the paper; :r 

 drains, repeat several tune-, when the-olid- may IK- con-id. 'red prac- 

 tically free ot salt- carried in solution, at least free enough for 

 qualitative tests. 



Closed tubes or matrasses are made from hard glass tubing 6 mm. 

 inside diameter. The tube is cut in I-'* cm. lengths ; the>e are heated 

 in the middle in the Hunsen burner flame until the glass softens, 

 constantly turning the tube; draw apart quickly until the two ends 

 part. Reheat the end that has been drawn out, while soft cut off 

 the extremity with an old pair of scissors, then fuse in the flame 

 until rounded. They should be cooled slowly or annealed to pre- 

 vent cracking when they are reheated while in use. 



The closed tube is used to heat substances out of contact with the 

 oxygen of the air, therefore there is little or no oxidation. Sub- 

 stain <- to be heated 

 should be in small frag- 

 ments or coarse powder, Flo 533 ._ Matra8g Holdcr . 

 and simply dropped to 



the bottom. The tube, held in the matrass holder, Fig. 533, is 

 heated with the 0. F. gently at first, finally increasing the heat 

 until the walls of the tube are fused. During the heating the 

 following phenomena are looked for. 



a. Water. Some minerals contain water of crystallization or 

 Mater of constitution ; the first is driven off at a comparatively low 

 temperature, the latter at a much higher temperature. This 

 water will collect in little drops or as a mistlike coat on the cold 

 walls of the upper end of the tube. It is needless to say that care 

 must always be taken that the open end is always cold 

 enough to condense the water. Heat a small piece of calamine 

 (Zn,SiO,.H 2 O). 



b. Sublimates are solids condensed on the cold walls of the tube, 

 formed of vapors driven from the mineral being heated. They 

 may be white or colored. Heat some arsenopyrite (FeSAs), 

 gently at first, when a bright red sublimate of sulphide of arsenic 

 will form, becoming brownish red as it collects. On continued 

 heating crystals of metallic arsenic will form a little below the 

 sulphide, finally forming a complete band or metallic mirror of 

 arsenic. 



c. Odors caused by escaping gases and acid fumes. 



d. Charring. The substance blackens and usually emits a 



