94 TETRAHEDRITE. 



The chlorine gas is to be passed through in a gentle 

 current only, especially towards the last, when the sub- 

 limation is effected, because otherwise the vapors of 

 the volatile products may pass unabsorbed through 

 the receiver. 



When the tube has become clear between the bulbs, 

 and the apparatus has cooled, it is cut through between 

 the bulbs by means of a file and a red-hot coal, and 

 the end with the bulb containing the sublimate is co- 

 vered with a short glass tube, sealed at one end and 

 moistened with water on the inside. The tubes are 

 allowed to remain connected in this manner for at least 

 twenty-four hours, in order to cause the sublimate 

 gradually to attract moisture and to prevent its becom- 

 ing hot and thus occasioning loss on being afterwards 

 dissolved in water, as would otherwise be the case. It 

 is then.dissolved in a little water, to which some hy- 

 drochloric and tartaric acids have been added, the tube 

 is carefully rinsed, and the rinsings added to the solu- 

 tion in the receiver. Should the liquid be cloudy, in 

 consequence of a separation of antimonious acid, a 

 gentle heat must be applied, in order to redissolve the 

 latter. In case of sulphur having separated in an un- 

 oxidized state, it must be filtered off. 



I. ANALYSIS OF THE FIXED EESIDUE. The bulb 

 containing it is placed in a beaker with dilute hydro- 

 chloric acid, and digested until the contents are dis- 

 solved, with the exception of the chloride of silver. 

 This is filtered off and treated as in No. 1. Should 

 chloride of lead be present, as is the case in the analysis 

 of bournonite, it must be dissolved by using a larger 

 quantity of water. In this case the contents of the 

 bulb have to be heated very cautiously, that the chlo- 

 ride of lead may not volatilize. 



A slow current of sulphuretted hydrogen is then 

 passed through the solution until it is completely satu- 



