164 PROCEEDINGS OF THE AMERICAN ACADEMY. 



The strongly smelling filtrate from this zincic sulphide, now freed from 

 all traces of the most usual metallic impurities, was treated with chlo- 

 rine water to oxidize any iron or manganese which might be present, 

 and precipitated fractionally with pure sodic carbonate. The first 

 fraction of the precipitate containing traces of iron and manganese was 

 thrown away. 



After a thorough washing the second fraction, containing most of the 

 zinc, was dissolved in pure nitric acid, keeping the carbonate in excess. 

 After filtration, the addition of a little ammonic carbonate, and another 

 filtration, the greater part of the zinc present was precipitated by means 

 of ammonic carbonate. When it had been subjected to a thorough wash- 

 ing the basic zincic carbonate was ignited in a double platinum crucible 

 over an alcohol lamp. The oxide thus obtained was washed repeat- 

 edly with water, for often an impurity which is held by a wet precipitate 

 may be washed out when the precipitate has been partially decomposed 

 or disintegrated by heat. Artus * has observed that the sodic carbo- 

 nate occluded in the quantitative precipitation of zinc may be easily 

 removed in this way, and the present experience showed that occluded 

 zinc chloride could be waslied away with equal ease. The zinc oxide 

 thus obtained was almost white, with a very faint tinge of yellow ; 

 upon solution in nitric acid it gave absolutely no opalescence with 

 argentic nitrate. Its method of preparation made the presence of 

 non-volatile impurities almost impossible, for it was precipitated from 

 a solution containing nothing but zinc, nitric acid, and ammonia. 



Preparation of Hydrohromic Acid. This substance was made by 

 the action of bromine on water in the presence of phosphorus. The 

 bromine was purified by the well known method of Stas,| having been 

 dissolved in a saturated solution of potassic bromide holding zinc oxide 

 in suspension, and distilled from this solution after long standing. The 

 bromine, thus freed from chlorine and iodine, was collected under 

 water and redistilled. Red phosphorus was now purified by very fine 

 pulverization under water and by repeated washing of the powder with 

 pure water. According to Stas this method removes every trace of 

 chlorine which may be held by the substance. Our own experience 

 has not been uniformly favorable in this respect, but upon this occasion 

 and several others both the qualitative tests for the absence of chlorine 

 and the quantitative analysis of the hydrobromic acid made with the 

 assistance of well washed phosphorus were satisfactory. The bromine 



* Berzelius, Jahresbericht, XXIII. 132. 

 t Mem. Acad. Belg., XLIII. Pt. II. 90, 38. 



