MODIFIED TECHNIC FOR FIRST-GROUP SEPARATION. REMOVAL OF LARGE AMOUNTS OF MERCUROUS CHLORIDE BY SUBLIMATION EUGENE W. BLANK,ALLENTOWN, PENNSYLVANIA
In the usual methods applied to the analysis of the firstgoup precipitate small amounts of lead cannot he extracted if large amounts of mercurous chloride are present owing to the occlusion of the lead by the latter. Likewise when the quantity of mercury is large and that of silver relatively small, ammonium hydroxide may fail to extract silver chloride owing to the fact that the latter is reduced by the liberated mercury to the metallic state ( I ) , (2), (3). In such cases special procedures must be resorted to. Schoorl ( 4 ) , working with micro quantities, advocated removing the interfering mercurous chloride by sublimation. The disadvantages inherent in a separation by sublimation have been overcome by several modifications in procedure described in this paper. T o a small portion of the washed precipitate containing the chlorides of silver, mercurous mercury and lead add several drops of ammonium hydroxide. If large amounts of mercury are indicated by the intensity of color of the black residue place the remaining precipitate in a small evaporating dish on a sand-bath. Cover the dish with a glass funnel and mount a thermometer in the sand. The sand-bath is heated gently a t first to dry the precipitate. The temperature is then slowly raised to 360°C. over a period of ten to twenty minutes depending upon the volume of sublimate evolved. Silver chloride (m. p. 455'C.) and lead chloride (m. p. 500°C.) remain unchanged by this treatment. Allow the apparatus to cool and analyze the residue in the evaporating dish by the usual procedure ( I ) , (Z), (3), with one modification. It is advisable to extract the lead with hot dilute hydrochloric acid instead of hot water in order to get the lead into solution. This is necessary since part of the lead chloride may have been converted into oxide or basic chloride by the heat treatment. The sublimate may be identified by the general tests applicable to mercurous mercury.
Literature Cited AND CURTMAN, "Qualitative Analysis," The MacmiUan Co., New (1) BASKERVILLE York City, 1917, p. 38. (2) GOOCH AND BROWNING, "Outlines of Qualitative Chemical Analysis," John Wiky and Sons, Inc., N e w York City, 1925, p. 25. ~LL ~ L L "Analytical , Chemisw," John Wiley and Sons. Inc., (3) T ~ E A D AND New York City, 1921, Vol. I, p. 303. ( 4 ) Sc~oonr,Z. anal. Chem., 47, 209 (1908).
