in the presence of Calcium and Magnesium. 525 



The experiments of Series G were made in exactly the same 

 manner as those of Series F, except that varying amounts of 

 magnesium chloride were present instead of the calcium salt. 

 The results are uniform and exact, and indicate that barium 

 may be separated from magnesium when the two are present 

 in any proportion. It is probable that if magnesium chloride 

 were present in an amount larger than 3 grm. in 30 cm 3 it 

 would be necessary to make two treatments, as under those 

 circumstances it shows a slight tendency to precipitate. The 

 amount of mixed salts present should always, therefore, be 

 kept below this limit. 



Recapitulation. — Barium chloride is soluble to an extent 

 not exceeding one part in 20,000 in pure concentrated hydro- 

 chloric acid, but the solubility increases very rapidly with the 

 diminution in the strength of the acid. In concentrated hydro- 

 chloric acid containing ether it is soluble to an amount not 

 exceeding one part in about 120,000. To utilize this fact for 

 the separation of barium from calcium and magnesium the 

 chlorides of the earths are dissolved in the least possible amount 

 of boiling water and precipitated by 25 cm 3 of concentrated 

 hydrochloric acid with the addition of 5 cm 3 of absolute ether 

 after cooling. The acid should be added drop by drop at first 

 allowing the precipitate formed to redissolve as long as possible, 

 as the precipitate is thus obtained in a coarse crystalline condi- 

 tion and filters very quickly and is less liable to include foreign 

 matter. After standing a few minutes the precipitate is to 

 be filtered in a Gooch crucible, washed with hydrochloric 

 acid containing about 10 per cent of ether and dried at 

 150°-200° C. The method is accurate and rapid, and pos- 

 sesses the further advantage "when a number of determinations 

 are to be made that the precipitate may be dissolved off of the 

 felt by a little water and, after ignition, the crucible and felt 

 may be used again without re-weighing. A felt upon which half 

 a dozen precipitates were weighed did not change its weight 

 to the extent of one-tenth of a milligram. The fumes of the 

 strong acid cause no inconvenience if the filtration is performed 

 in front of a good flue. A gas flame may be used in the flue 

 without danger from the ether which seems to be firmly held 

 by the hydrochloric acid. A flame was used to increase the 

 draught in all of the experiments given and with entire safety, 

 even when the filtrate contained 50 per cent by volume of 

 ether. 



The author wishes in concluding to acknowledge his indebt- 

 edness to Prof. Gooch for many helpful suggestions freely 

 given in the course of the investigation. 



