ASHES OF PLANTS. 231 



brown color), separated according to No. 19. From 

 the filtrate, the lime is precipitated by oxalate of am- 

 monia, and the magnesia as phosphate of magnesia- 

 ammonia, by merely adding an excess of ammonia ; 

 the phosphoric acid previously in combination with 

 the lime is calculated from the loss. If manganese be 

 present, it is precipitated together with the phosphate 

 of magnesia-ammonia, to which it imparts a gray or 

 black color after ignition. The separation is effected 

 as in No. 26. 



The solutions from which the phosphates have been 

 precipitated by ammonia, now contain only the alka- 

 lies and the remainder of the phosphoric acid. The 

 latter is precipitated (together with sulphuric acid) by 

 chloride of barium, and the excess of baryta removed 

 by sulphuric acid or by neutral carbonate of am- 

 monia ; the filtrate is evaporated to dryness, the residue 

 ignited, and the alkalies weighed as chlorides or sul- 

 phates. For their separation, see No. 4. The preci- 

 pitate produced by chloride of barium is exhausted 

 with nitric acid, sulphuric acid added to effect the 

 complete separation of the baryta, and the phosphoric 

 acid precipitated from the filtrate, previously mixed 

 with an excess of ammonia, as phosphate of magnesia- 

 ammonia. 



II. Ashes of wood, vegetables, &c. Of those vegetables 

 which yield a large amount of ash, 50 grms. may be 

 taken for examination ; but of the different kinds of 

 wood, which are usually poorer in mineral constituents, 

 and of the Graminacede, the ash of which contains 

 much silica, about 100 grms. should be employed. 

 The substances are carbonized in a platinum crucible, 

 and the mass thrown immediately into a flat porcelain 

 dish, where it generally smoulders for a long time, 

 and is, for the most part, converted into ash. The 

 incineration is completed in the platinum crucible. 



The analysis of these ashes only differs from that 



