DR, T. S. HUMPIDGE ON THE ATOMIC WEIGHT OF GLUCINUM. 
603 
in a large leaden dish, which is furnished with a leaden lid, and is heated on a 
water-bath for two or three hours. The remaining sulphates are next heated in an 
iron crucible to expel the excess of acid and any traces of silica, then dissolved in warm 
water and the calcium sulphate filtered off. To the filtrate, sufficient potassium sulphate 
is added to form alum with the alumina present, and the solution evaporated down to 
crystallize. The mother-liquor, from which nearly the whole of the alumina has been 
thus removed, is then slowly dropped, best by a separating funnel, into a large excess 
of warm concentrated ammonium carbonate solution, with constant stirring. About 
ten times as much of the salt is necessary as the quantity of glucina supposed to be 
present. The whole is then placed in stoppered bottles, and allowed to stand for four 
or five days, after which no change appears to take place. At the end of this time the 
solution, which contains nearly the whole of the glucina, some alumina, and often not 
inconsiderable quantities of iron, is then filtered, and colourless sodium sulphide added 
as long as ferrous sulphide is thrown down. If the quantity of iron present produces 
only a coloration, but no precipitate, it is well to add a little ferric chloride, and then 
i completely precipitate with sodium sulphide. This is the only method I know of, except 
fusion with acid potassium fluoride, which removes every trace of iron. In the filtered 
solution the ammonium carbonate is now to be decomposed by boiling, but if the 
concentrated solution is heated directly over the flame very violent bumping cannot be 
avoided. A better plan is either to dilute freely with water (to about three times the 
bulk), or else to warm for about two hours over a water-bath, and when most of the 
ammonium carbonate has been decomposed, then to boil over the flame. The final 
traces of the carbonate are removed by acidulating with hydrochloric acid, yielding a 
solution from which ammonia precipitates the hydrate. By repeating the process 
the glucina is obtained nearly pure. Absolutely pure it can only be prepared from 
the double potassium fluoride, K :j G 1F 6 , by fusion with acid potassium fluoride, and 
recrystallizing the double fluoride from hot water. The quantity of the acid fluoride 
required by theory (6:1) should be used, not only 2:1, as recommended by Dr. 
Wolcott Gibbs, who, I believe, first introduced the process. The purified double 
fluoride is then readily decomposed by the requisite quantity of concentrated sulphuric 
acid in a platinum dish, and the hydrate precipitated with ammonia in the usual manner. 
A very good yield may be obtained from beryl by this hydrofluoric acid process, 
provided the mineral is sufficiently finely powdered. Fairly pure compounds of 
glucinum may, however, be now obtained from some continental manufacturing 
chemists, which only require once purifying with ammonium carbonate for all ordinary 
purposes. 
III. Separation of metallic glucinum. 
Metallic glucinum may be obtained either from its double fluoride with potassium 
or from its chloride, of which the latter is decidedly the most suitable compound. 
The double fluoride, K 3 G1F 6 , melts at a low red-heat without decomposition. 
