and Laboratory Methods. 1291 



tium sulphate are obtained from hot H2SO4 ; more barium is apt to alter the 

 usual crystal form, although the appearance of the crystals separating, still sug- 

 gests the strontium sulphate type. An excess of barium seems to cause the 

 majority of the crystals to assume forms somewhat resembling barium sulphate. 

 In general, crystals of both strontium and barium sulphate can be distinguished 

 in mixtures of these two elements. 



Any lead which may be present will be precipitated in an amorphous condi- 

 tion by the dilute acid. Recrystallized from hot sulphuric acid, the lead sulphate 

 will separate in forms which at first closely resemble those of strontium sulphate 

 and which, later, grow to forms which may be mistaken for barium sulphate. 



Recrystallized from hydrochloric acid there is less danger of confusion. If 

 in doubt, extract the precipitated sulphates with a solution of potassium or sodium 

 hydroxide in which lead sulphate is soluble. 



As in the case of calcium, chlorides of the trivalent metals and salts of boric 

 acid may sometimes interfere with the formation of typical crystals of strontium 

 sulphate. 



£xercises for Practice. 



To a drop of a moderately dilute solution of SrCl2 add dilute H2SO4 and 

 examine at once. 



Recrystallize SrSO^ from HgSO^; and from HCl. 



Try to recrystallize from HCl in the presence of H2SO4. 



Make a mixture of calcium and strontium and add HgSO^. Recrystallize 

 the product from H2SO4 without having removed the calcium. In another por- 

 tion remove the calcium by extracting with boiling water and then recrystallize 

 the residue. 



See also exercises suggested under Barium. 



//. Sfroiitinm Oxalate is precipitated from solutions of salts of Strontium by 

 Oxalic Acid. 



SrCl2 + H2C0O4 = SrC204 . ;/H20 + 2HC1. 



Method. — Proceed as directed under Calcium, Method II. Strontium oxa- 

 late is precipitated at once. The crystals of this salt are similar to those obtained 

 with calcium, but are somewhat larger and crosses are more pronounced ; yet 

 when dealing with mixtures of unknown composi- 

 tion, the difference is scarcely sufficient to permit 

 of strontium being distinguished from calcium. 



The crystal forms of strontium oxalate which 

 are most frequently met with are shown in Fig. 52. 



Remarks. — Either tetragonal or monoclinic 

 crystals are obtained as in the case of calcium. 



The remarks under Calcium (q. v.) apply 

 equally well to strontium. 



It is always advisable to draw off the super- 

 natant solution and add dilute sulphuric acid to Fig. 52. 



