USE OF THR BLOWriPE. 



67 



reous spar,) when dropped into either of these acids gives off 

 bubbles of gas, which effect is called effervescence. The 

 same result takes place with some other minerals. The 

 acid used in these tests, should be half water ; and to avoid 

 error, it is best to put a little of it in a test tube, and drop in 

 small fragments of the coarsely powdered mineral. Some- 

 times heat will cause an effervescence, which does not take 

 place with cold acid. Often effervescence arises from some 

 impurity present, which is discontinued before the solution 

 if the mineral in the acid is complete. 



Other minerals, that do not effervesce in the acids, be- 

 come changed to a jelly-like mass. For trials of this kind, 

 the strong acids should generally be used. The powdered 

 mineral is allowed to remain for a while in the acid, and 

 gradually a jelly-like mass is formed. Often heat is required, 

 and in that case, the jelly appears, as the solution cools. 

 The minerals belonging to the zeolite family more especially 

 undergo this change from the action of acids, and it arises 

 from the separation of their silica in a gelatinous state. 



BLOWPIPE. 



To ascertain the effect of heat on minerals, a small instru. 

 ment is used called a blow- 

 pipe. In its simplest form, 

 (fig. 100,) it is merely a bent 

 tube of small size, 8 to 10 

 inches long, terminating at 

 one end in a minute orifice, 

 not larger than a pin hole. 

 It is used to concentrate the 

 flame of a candle or lamp on 

 a mineral, and this is done 

 by blowing through it while 

 the smaller end is just within 

 the flame. 



Figures 101 and 102 are 

 other forms of the blowpipe, 

 containing air chambers (o) 

 to receive the moisture which 

 '" condensed in the tube 



d L. 



100 



101 



102 



rr 



& 







[J 



\ 



d 



[_ 



I 



a 



4=4=5 



What is effervescence, and how produced 1 How should the acid be 

 «sed 1 How are some minerals made to gelatinize ? On what does 

 hip property depend ? What is the object of a blowpipe ? 



