92 TETRAHEPRITE. 



absent, and generally they may replace each other in 

 the different kinds in varying quantities. 



The analysis is best effected by gently heating the 

 mineral in dried chlorine gas, when sulphur, arsenic, 

 antimony, mercury, and a portion of the iron are vola- 

 tilized in the form of chlorides, and copper, silver, zinc, 

 and part of the iron remain behind, likewise converted 

 iuto chlorides. 



The above figure shows the construction of the ap- 

 paratus to be used in such analyses. The chlorine gas, 

 for the purpose of drying it, is first passed through a 

 small cylinder containing concentrated sulphuric acid, 

 and thence through the chloride-of-calcium-tube, which 

 is fixed upon a wooden stand. 



The mineral, finely divided, is weighed in the bulb- 

 tube. The latter is best provided with two bulbs, in 

 order to collect the greater portion of the sublimate in 

 the second bulb, and thus to prevent the tube from 

 being stopped up. 



The end of the tube bent downwards is connected 

 by means of a good cork or a caoutchouc tube, with 

 the three-bulb-tube or receiver, hi which the volatile 

 products are to be condensed. The other end of the 

 latter is provided with a small conducting tube, through 

 which the excess of chlorine passes into a small flask 

 containing alcohol, or milk of lime. 



In order to prevent the precipitation of antimony, 

 the three-bulb receiver is not filled with pure water, 

 but with a mixture of dilute hydrochloric and tartaric 

 acids, whenever that substance is present ; the liquid 

 should fill about of the two upper bulbs, which will 

 require about 50 grins. In this arrangement the liquid 

 cannot rise above a certain point in either limb, but 

 must flow back again whenever it has been raised to a 

 certain height. 



If such a bulb-receiver be not at hand, a flask with 

 two necks may be used, as shown in the annexed 



