FOR SEPARATING THE ALKALINE EARTHS. VICKERY. 35 



90 mg. gave small i:»rcc'ipitate on standing an hour. 

 75 mg. gave no precipitate on standing. 

 Thus, under the conditions of ordinary work, calcium 

 when present in excess of 90 mg. is precipitated along with 

 the strontium. 200 mg. of calcium, and 40cc of (NH4)2S04 

 gave a heavy precipitate on warming, but no solvent action 

 was noticeable on boiling; 40cc more were added and boiled 

 and a slight solvent action took place. On adding 40cc of 

 ammonium chloride to this solution it was observed that 

 the greater part of the precipitate went into solution on 

 boiling for a few moments. As this action appeared import- 

 ant, it was determined to investigate it further. 



To try the effect of the addition of ammonium chloride 

 before precipitating the sulphate, two solutions of 400 mg. 

 of calcium each were prepared. To Xo. 1 were added 

 40cc XH4CI and to each Ice of acetic acid. Both were 

 brought to 70° and lOcc (NH4)2 SO4 added. The effect of 

 the ammonium chloride was very noticeable, for in five 

 minutes only a very few cry.stals had appeared in Xo. 1, 

 and very little deposit had formed on the bottom of the 

 beaker, while in the second beaker the precipitation had 

 been heavy and was nearlj^ complete. Other experiments 

 were tried, and it was found that 80cc of ammonium chloride 

 solution were sufficient to prevent completely the precipita- 

 tion of 200 mg. of calcium, while 50cc failed to do so, as a 

 slight deposit formed on boiling. 160cc were sufficient to 

 hold up 400 mg. of calcium, showing that there should be 

 80cc of ammonium chloride present for each 200 mg. of 

 calcium. It was found that the total volume should be 

 not less than 150cc as a smaller volume rendered the precipi- 

 tation of the calcium more likely. The effect of the am- 

 monium chloride upon the strontium was investigated, and 

 it was found that in the presence of a large excess, 4 mg. gave 

 a precipitate on boiling, while 3mg. gave a very slight tur- 

 bidity. Thus the effect is scarcely appreciable. The amount 



