108 WATER-ABSORPTION AND TRANSPIRATION. 



(6) Place about 10 grammes of ash in a 500 c.c. flask, moisten it with 

 a small quantity of strong nitric acid, then add about 20 c.cs. strong 

 hydrochloric acid and heat on a tripod (or " digest " it for half an hour 

 on a water- or sand-bath at boiling-point). Rinse the contents of the 

 flask into an evaporating basin and heat to dryness. Moisten the 

 residue with strong hydrochloric acid, add about 200 c.cs. of water, and 

 filter. Make the filtrate up to 600 c.cs. with water and divide it into 

 four parts. 



(i) To one part add, in a large test-tube, some barium chloride 

 solution. The finely-divided white precipitate (barium sulphate) in- 

 dicates the presence of sulphur (as sulphuric acid). Verify this by 

 mixing some dry ash with carbonate of soda, heat on charcoal with the 

 reducing blowpipe-flame, and (1) put a few drops of dilute hydrochloric 

 acid on the fused mass (the sulphuretted hydrogen given off is easily 

 recognised by its odour), (2) put a little of the mass on a silver coin 

 and add a drop of dilute acid (a black stain of silver sulphide is 

 formed). These " dry " tests may fail, however, if but little sulphuric 

 acid is present. 



(ii) To some ash-solution in a test-tube add an equal bulk of strong 

 nitric acid, then three or four times its bulk of ammonium molybdate. 

 A yellow precipitate indicates presence of phosphorus (as phosphoric 

 acid). 



(iii) To test for iron, add potassium ferrocyanide : a dark blue pre- 

 cipitate (Prussian blue) is produced. 



(iv) It is necessary to remove the phosphates from the ash solution, 

 as follows. Neutralise with ammonia, then add acetic acid till the 

 solution is distinctly acid again, and then ammonium acetate in excess. 

 Now add ferric chloride till no further buff-coloured precipitate (ferric 

 phosphate) is produced and the solution becomes red (owing to ferric 

 acetate). Boil the solution till it is colourless, filter, and reject the 

 precipitate. 



To the solution thus obtained add ammonium chloride, ammonia, 

 and ammonium carbonate ; a white precipitate indicates the presence 

 of lime. Filter, and to the filtrate add sodium phosphate ; a white 

 precipitate (often formed only after shaking the liquid and letting it 

 stand for some minutes) shows that magnesia is present. 



Filter, evaporate the filtrate to dryness, and test the residue for 

 soda and potash. Add a few drops of platinic chloride to the residue, 

 evaporate again, then add some alcohol ; a yellow crystalline precipi- 

 tate shows that potash is present. Or dip a clean platinum wire into 

 hydrochloric acid and hold it in a Bunsen or spirit-lamp flame until it 

 no longer colours the flame yellow (owing to presence of soda). Then 

 dip the wire, moistened with hydrochloric acid (strong), into the residue 

 and put it in the flame. Potash turns the flame violet, but if the 

 yellow (soda) colour is too strong look at the flame through a thick 

 piece of blue glass : the soda colour is cut off and the reddish-violet 

 potash flame is seen. 



If you are working in a chemical laboratory, you should try to make 

 rough quantitative analyses of the ash of a few plants, using the 

 methods given above, with the help of a book on Quantitative Analysis. 



