BAXTER AND STEWART. — PRASEODYMIUM CHLORIDE. 187 



These experiments agree very satisfactorily with those in which the 

 praseodymium and chlorine were actually determined, in indicating 

 beyond question that the insoluble residue is the oxychloride. 



The surprising feature of these results is that the amount of insol- 

 uble matter increases with the period of fusion instead of decreasing 

 or even remaining constant. The obvious conclusion is that some 

 source of oxygen exists in the fusion atmosphere. To be sure, in the 

 first of the experiments for the determination of the insoluble residue 

 a tiny hole was discovered in one of the fused joints of the hydrochloric 

 acid apparatus, and in this experiment the weight of insoluble residue 

 was found to be about ten times as large as in the subsequent experi- 

 ments. Fortunately the defective joint was a comparatively new one, 

 and could have affected only four of the fusions of the salt for analyses. 

 The Analyses involved are Nos. 12, 13, 14, 15, 34, 35, 36 and 37. The 

 hole was excessively small, however, and it is not at all certain that 

 any real difficulty was produced. It seemed possible that the hydro- 

 chloric acid gas might contain air, originating in the reagents used for 

 generating the gas, or possibly from incomplete sweeping out of the 

 purifying train. By passing the hydrochloric acid gas into water 

 under an inverted tube after the apparatus had been thoroughly 

 swept out, we found that it actually did contain a trace of air. We 

 tried in some experiments to avoid the first difficulty by passing the 

 hydrochloric acid gas through a hydrochloric acid solution of cuprous 

 chloride before it entered the drying towers, and in order to avoid the 

 second difficulty the apparatus was swept out even longer than before 

 previous to the fusion of the salt, but neither of these remedies seemed 

 to have any effect upon the formation of the basic salt. Another 

 source of oxygen might be moisture. However, concentrated sul- 

 phuric acid has been found by Morley 27 to be a very effective dry- 

 ing agent. One liter of gas passed over concentrated sulphuric acid 

 retains only . 003 mg. of moisture. In order to make sure that the 

 hydrochloric acid was really as dry as this, the gas was passed for 

 several hours through a U- tube cooled with alcohbl and solid carbon 

 dioxide. A very small amount of white solid was condensed in the 

 tube, presumably a hydrate of hydrochloric acid. But even on the 

 assumption that all of the moisture is removed from the gas by the salt 

 during the fusion, it seems impossible that the residue should have 

 formed wholly from moisture contained by the acid gas. Still another 

 possibility was that the quartz tube was attacked by the acid gas to 

 yield moisture and a chloride of silicon. This point was tested by 



27 Am. J. Sci., 30, 141 (1885). 



