CHAPTER I 

 PRELIMINARY EXAMINATION 



Much, time may be saved in the determination of unknown 

 substances if a preliminary examination be carried out. 



Physical Characters 



A. If a fluid, note (1) the colour, (2) transparency. (3) odour, (4) 

 viscosity, (5) specific gravity, and (6) reaction. If a deposit be 

 present or if the fluid be opaque, an examination with the micro- 

 scope should be carried out. 



B. If a solid, note (1) the colour, (2) form amorphous, crystal- 

 line, fibrous, etc., (3) consistence tough, elastic, hard, soft, etc., 

 (4) odour, (5) solubility in various media : (a) cold, (6) hot (1) 

 water, (2) 5 per cent, sodium chloride solution, (3) dilute sodium 

 hydrate, (4) dilute mineral acid (HC1), (5) alcohol, (6) ether (take 

 care no free flame is near). 



Chemical Characters 



Burn a portion of the substance, or residue after evaporation of a 

 fluid, on a piece of platinum foil. Note (1) changes in substance, 

 (2) odour, (3) ash, if any. 



Test for the presence of nitrogen, sulphur and phosphorus. 



Into a small hard glass test tube, or a small length of hard glass 

 tubing fused at one end, place a very small portion of the finely- 

 powdered substance to be tested, then add fragments of clean 

 metallic sodium amounting in all to the size of a pea, and another 

 small portion of the substance. Heat at first gently, then strongly 

 until the glass is bright red in colour. Cool and when nearly cold 

 break into a dry evaporating basin under a piece of wet filter paper. 

 After a few minutes add about 15-20 c.c. water, heat to boiling, 

 then filter. Test nitrate. 



Nitrogen. To 5 c.c. add a few drops of 0-5 per cent, ferrous 

 sulphate and one or two drops 0-5 per cent, ferric chloride. Boil, 

 then cool and acidify with concentrated HC1. If nitrogen be 

 present a blue solution containing particles of Prussian blue is 

 obtained. 



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