TETRAHEDRITE. 93 



figure. The perpendicular limb of the bulb-tube almost 

 touches the mixture of acids in the receiver, but does 



13. 



not dip into it, because the liquor might in that case 

 recede into the bulb-tube, the chlorine being rapidly 

 absorbed. The conducting-tube, inserted through the 

 second neck, expands at its upper portion into a bulb, 

 and is cut off below in an oblique direction ; it enters 

 the liquid -so far, that this can be pressed up into the 

 bulb only, and must then flow back again. To this 

 tube a second one is attached, which is bent at a right 

 angle, and conducts the excess of chlorine into alcohol, 

 or milk of lime. 



It is advisable not to connect the bulb-tube, contain- 

 ing the mineral, with the chlorine apparatus, until 

 most of the atmospheric air has been expelled from it. 



The complete decomposition of tetrahedrite takes 

 place even at the ordinary temperature, with strong 

 evolution of heat. When the bulb has nearly cooled 

 again, it is heated gently by a very small flame, in 

 order to separate the volatile products from the non- 

 volatile, and to drive the former into the second bulb. 

 It is scarcely possible to drive off all the sesquichloride 

 of iron ; the heating is therefore discontinued as soon 

 as vapors of this compound only appear to be evolved. 



