1292 Journal of Applied Microscopy 



the precipitate. If no crystals of calcium sulphate appear, add more acid, heat 

 until white fumes appear, cool and examine the preparation for crystals of 

 strontium sulphate (see Method I). 



Exercises for Practice. 



See exercises suggested under Barium. 



///. With Sodium Tartrate solutions of salts of Strontium yield difficultly solu- 

 ble Stroutium Tartrate. 



SrCla + HNaC^H^Og = SrC^H^Og . 4H2O + NaCl + HCl. 



Method. — Proceed as directed under Calcium, Method III. Strontium tar- 

 trate is isomorphous with calcium tartrate and is not to be distinguished from the 

 latter (see Fig. 47). There is, perhaps, a tendency on the part of the strontium 

 compound to form shorter and stouter prisms and thin plate-like crystals in 

 greater abundance than is the case with the calcium salt. 



Remarks. — See remarks under Calcium. It is not possible to distinguish 

 between calcium and strontium by this test. 



Behrens suggests the addition of magnesium acetate and acetic acid to the 

 mixture thought to contain both elements, before introducing the reagent. This, 

 he states, retards the reaction and prevents the normal development of the cal- 

 cium salt while the strontium tartrate grows to its usual size. Such a modifica- 

 tion of the test requires considerable experience in order that just the proper 

 conditions shall be obtained ; for this reason the modification is seldom success- 

 ful in the hands of a beginner. 



The test is useless in the presence of barium and many other elements ; the 

 most important of these being lead, iron and aluminum as chlorides, and boron 

 as borates. 



IV. Ammonium Dichromate in alkaline solution precipitates Strontium Chromate. 

 2SrCU + (NH j2Cr207 -|- 2NH4OH = 2SrCr04 + 4NH4CI + H2O. 



Method. — To a dilute neutral or very slightly acid 



xV S^ solution of the substance to be tested add a fragment 



^fi^/y of ammonium dichromate (or potassium dichromate). 



jg, A No precipitate should result if only strontium is present. 



i^<^^ Should a precipitate result, draw off the clear liquid 



^ ^'tf after all the reagent has dissolved; then add to it a 



^ *J?^ ^ small drop of ammonium hydroxide. Strontium chro- 



•^^ *<>^^^^^^ mate immediately separates in tiny yellow globulites or 



11,1 dumb-bell-like forms. Near the circumference of the 



" *" drop short rods appear later (Fig. 53). Warming 



gently, hastens the separation. 



Remarks. — Unless care is taken to employ a sufficiently dilute solution, the 



precipitate obtained will consist of such minute granular masses as to appear to 



be amorphous. 



The addition of sodium acetate in excess will also cause the precipitation of 

 strontium chromate. 



