380 ELEMENTARY CHEMICAL MICROSCOPY 



PHOSPHATES. 



a. To the drop to be tested, add a drop of Nitric Acid. Then 

 apply a drop of Ammonium Molybdate by Method /, page 251. 

 Warm gently. Phosphates yield a yellow precipitate appearing 

 amorphous under the microscope unless a magnification of over 

 200 is employed. A similar reaction will be obtained if silico- 

 molybdates or arseno-molybdates are formed. 



This reaction is of value if arsenic and soluble silicates are 

 absent and as indicating whether much or little phosphate is 

 present. If a heavy precipitate is obtained, apply test b. 



b. To the Ammoniacal Solution add Ammonium Chloride and 

 Magnesium Acetate, proceeding as described under Magnesium, 

 page 305. Arsenates must be absent. 



Note. Phosphates frequently interfere with the detection 

 of certain bases and must be removed before reliable reactions 

 can be obtained; their removal may be accomplished by means 

 of tin in acid solution. Acidify with nitric acid, add a few tiny 

 bits of pure tin-foil and as soon as the reaction has ceased, heat 

 to boiling. Cool and extract the material with dilute nitric 

 acid. 



SILICATES. 



a. Treat the material upon a celluloid object slide with am- 

 monium fluoride, sodium chloride and sulphuric acid. Sodium 

 silicofluoride is formed. See Sodium, page 278. Boron, zirco- 

 nium and titanium must be absent. 



SULPHATES. 



a. To the drop add a trace of Nitric Acid, then a drop of Cal- 

 cium Acetate by Method /, page 251. Characteristic needles or 

 prisms of calcium sulphate result. See Calcium, page 288. 



b. To the drop add a trace of Potassium Chromate, a trace of 

 Nitric Acid and a drop of Silver Nitrate. Characteristic crystals 

 of silver sulphate will be obtained, stained yellow through solid 

 solution of the silver chroma te. See Silver, page 335. 



