1498 Journal of Applied Microscopy 



with a dilute solution of ammonium hydroxide; Mg, Zn, Cd, Ni, Cu are dissolved. 

 To the solution add oxalic acid and acetic acid and from the precipitated 

 oxalates of Zn, Cd, Ni, and Cu, the clear solution is separated by decantation, 

 filtration, or the centrifuge. This solution is evaporated with sulphuric acid and 

 heated to destroy the oxalic acid. The residue is dissolved in acidulated water, 

 treated with sodium hydroxide, the precipitate carefully washed, dissolved in 

 hydrochloric acid and tested for magnesium with sodium phosphate. 



C. Magnesium from Glucinitm. 



To the solution to be tested add ammonium chloride, then carefully, a little 

 at a time, ammonium hydroxide as long as a precipitate results, draw off at once 

 and test the decanted solution with sodium phosphate for magnesium. 



ZINC. 



A. Zinc from Gluciniim, Magnesimn, and Cadmium. 



Ignite, warm gently with sodium hydroxide solution. Zinc and glucinum are 

 dissolved, magnesium and cadmium remain in the residue. Separate the solu- 

 tion, add to it acetic acid and precipitate the glucinum with potassium oxalate 

 (a little zinc is always precipitated with the glucinum). Separate the clear solu- 

 tion, evaporate and destroy the oxalic acid by means of sulphuric acid and heat. 

 Take up the residue with water, acidified if necessary, add ammonium acetate, 

 and test for zinc with sulphocyanate ; the addition of a trace of copper will 

 increase the delicacy of the reaction. Or, instead of testing with sulphocyanate, 

 to the sodium hydroxide solution after the removal of the magnesium and cad- 

 mium, add ammonium carbonate, zinc will separate as the double carbonate of 

 zinc and sodium. 



B. Zinc fr inn Cadmitcm. 



Precipitate with primary sodium carbonate in ammoniacal solution, cadmium 

 separates at once, draw off the supernatant solution and allow to stand for a 

 short time, zinc separates as the double carbonate. Or, acidify the solution to 

 be tested, and to it add powdered metallic magnesium. Zinc and cadmium are 

 precipitated. Wash carefully the finely divided metallic mass; add acetic acid, 

 heat the preparation ; zinc passes into solution with but very little cadmium, 

 decant and test for zinc. The residual metallic cadmium is dissolved in hydro- 

 chloric acid and tested. 



C. Zinc in Complex Afixtures. 



Treat with ammonium hydroxide and hydrogen peroxide. Then with 

 ammonium carbonate. To the decanted solution add oxalic acid and acetic 

 acid. Separate the precipitated oxalates, ignite and extract the zinc with sodium 

 hydroxide. The clear solution containing the zinc is heated with ammonium 

 chloride and tested for zinc with primary sodium carbonate or acidified and 

 tested with sulphocyanate. 



