1330 



Journal of Applied Microscopy 



<:::^ 



When dealing with mixtures of Ca, Sr, and Ba, 

 Behrens suggests the addition of a little acetic acid 

 prior to that of the oxalic acid, then by cautiously 

 neutralizing with magnesium carbonate, one element 

 after another can be caused to separate. This method 

 of procedure requires great care and considerable 

 experience. For this reason it generally fails in the 

 hands of the beginner. 



///. Sulphuric Acid. 



The method of procedure has already been 

 thoroughly discussed. Attention has been called to 

 the fact that from mixtures of the sulphates, Ca can 

 be extracted with hot water; Sr (and Pb) with hot hydrochloric acid; Ba 

 remaining unacted upon. 



Concentration of the water extract will give crystals of calcium sulphate. 

 Evaporation of the hydrochloric acid solution yields crystals of strontium 

 sulphate. 



The residual barium sulphate can be recrystallized from sulphuric acid, or can 

 be converted into barium carbonate, dissolved, and tested. 



l*ig-63. 



With simple mixtures it is often unnecessary to proceed according to the 

 above methods. Combinations of the different tests can be resorted to. For 

 example, Ba can be precipitated in acetic acid solution by means of ammonium 

 dichromate. The clear liquid is decanted, ammonium chloride and potassium 

 ferrocyanide added, and the Ca precipitated and identified. The clear liquid is 

 again separated and tested for Sr with sulphuric acid or potassium sulphate. 

 The precipitated strontium sulphate can then be washed and recrystallized. 



In addition to the above methods, it is possible to effect a fair separation by 

 converting into nitrates, evaporating, and drying carefully. The perfectly dry 

 nitrates can then be extracted with a mixture of absolute alcohol and ether. Ca 

 nitrate is quite soluble, Sr nitrate much less so, while Ba nitrate is practically 

 insoluble. 



The alcohol-ether extract is evaporated to dryness, the residue dissolved in 

 water, and tested for Ca with sulphuric acid, arsenic acid, or potassium ferro- 

 cyanide. The residual nitrates, insoluble in the alcohol, can then be tested for Sr 

 and Ba by the dichromate method, or with stannic chloride and oxalic acid, or 

 ferric chloride, sodium acetate, and oxalic acid ; or oxalic acid in nitric acid 

 solution. 



In all cases the choice of method must be governed by the nature of the sub- 

 stance being examined. The ability to select, at once, the proper method of pro- 

 cedure which will yield the requisite information in the shortest possible time, 

 and without error, is to be acquired only by experience and much practice. 



E. M. Chamot. 

 Cornell University. 



