34 AX INVESTIGATIOX OF THE " CHROMATE METHOD " 



minutes. 5 mg. gave a precipitate almost at once. Boiling 

 temperature m'sls used. 



STROXTIUM CHROMATE 



Precipitating reagent, 15cc K2Cr04. Total volume of 

 solution, 200cc. 



In neutral solution 200 mg. of strontium gave a very 

 slight deposit in beaker in ten minutes. 400 mg. gave a 

 heavy precipitate in a few moments. In solution containing 

 acetic acid, 500 mg. failed to give a precipitate over night. 



CALCIUM CHROMATE 



Conditions same as in precipation of 'strontium chromate. 



In neutral solution 500 mg. of calcium gave a barely 

 perceptible precipitate in fifteen minutes, while in acid solu- 

 tion none formed at all. 



The barium chromate when suddenly thrown down is 

 very fine and scarcelj- crystalline, but boiling for a few 

 minutes causes it to crystallize. Under the conditions of 

 ordinary work there is little risk of obtaining a precipitate 

 of strontium chromate, while the barium is almost completely 

 removed. 



STRONTIUM SULPHATE 



Precipitating reagent, lOcc (NH4)2 SO4. 



2 mg. failed to give a precipitate on boiling while 2.5 mg. 

 gave a scarcely perceptible one. 4 mg. gave very slight 

 precipitate on standing. lOmg. gave a precipitate in a few 

 moments. The experiments were repeated with both neutral 

 and acetic acid solutions, with practically identical results. 



CALCIUM SULPHATE 



Precipitating reagents, 2cc acetic acid, lOcc (NH4)2S04. 

 Temperature, 70°C. 



200 mg. gave heavy feathery precipitate at once. 

 100 mg. gave small precipitate in one minute, which 

 rapidly increased in size. 



