Test for Calcium

Crystal formation is indicative of the presence of calcium. Confirmation requires adding several drops of stock H2SO4 to dissolve the precipitate. Add several milliliters of methanol and heat gently. Precipitate (calcium sulfate) will reappear. 

Interpretation Microscopically, this calcium sulfate appears as elongate fiberlike crystals. 

---

Purified Talc When preparing solution A in the test for Calcium, add 1 M. H2S04. No effervescence produced. 

John A. L. Campbell. Did you test for calcium in analyzing the unknown particle with the electron probe ... 

The mixture is then cooled by surrounding the crock with cold water, and about 1700 g. of cold 50 per cent sulfuric acid is added, until a filtered sample just fails to yield a further precipitate of calcium sulfate upon the further addition of sulfuric acid. The calcium sulfate is filtered off and washed with cold water. A saturated aqueous solution of oxalic acid is cautiously added to the filtrate until a filtered sample gives no test for calcium salts in solution (Note 4). 

The chemical examination of this product is usually limited to a few qualitative tests. A portion is treated with hot dilute hydrochloric acid, and the filtered liquid tested for calcium and sulphuric acid (chalk, gypsum). Another portion is either treated with hot concentrated sulphuric acid or fused with potassium bisulphate when cold the mass is treated with water and the solution tested for aluminium. 

Mars yellow may be distinguished from ochre by qualitative analysis, especially by the tests for calcium sulphate, alumina as such, and zinc oxide. 

Test 2. A 1 in 20 solution responds to the oxalate test for calcium, and to the flame test of sodium. 

Identification A 1 10 aqueous solution gives positive tests for Calcium and for Acetate, Appendix IHA. 

Identification A sample dissolves, with effervescence, in 1 A acetic acid, in 2.7 A hydrochloric acid, and in 1.7 A nitric acid, and the resulting solutions, after boiling, give positive tests for Calcium, Appendix IIIA. 

B. Mix 1 g of sample with 20 mL of water, and add sufficient glacial acetic acid to effect solution. The resulting solution gives positive tests for Calcium, Appendix IIIA. Assay Not less than 95.0% and not more than 100.5% of Ca(OH)2. 

B. A sample gives positive tests for Calcium, Appendix III A. 

A. Mix about 500 mg of sample with 10 mL of 2.7 N hydrochloric acid, filter, and neutralize the filtrate to litmus paper with 6 N ammonium hydroxide. The neutralized filtrate gives positive tests for Calcium, Appendix IIIA. 

A. Heat 1 g of sample with a mixture of 25 mL of water and 5 mL of hydrochloric acid. Fatty acids are liberated, floating as an oily layer on the surface of the liquid. The water layer gives positive tests for Calcium, Appendix IIIA. 

Calcium sulphate dihydrate (microscope) test This is an excellent confirmatory test for calcium in Group IV it involves the use of a microscope (magnification about 110 x). The salts should preferably be present as nitrates. 

Magnesium behaves analogously to calcium, but strontium is not precipitated from concentrated solutions. Thus the ferrocyanide reaction can be used to test for calcium in the alkaline earth group. 

Of these, the calcium salt is notable for its extremely slight solubility in water. This property is utilized to test for calcium in very low concentrations. The reagent is not specific and other metals, with the exception of alkali and ammonium salts, should not be present. Magnesium does not interfere provided its quantity is not more than 10 times the amount of calcium present. In higher concentrations, the magnesium salt is precipitated in the cold on heating, it is soluble. At the same time, for reasons that are not known, the precipitation of the calcium compound is completely prevented. 

---