238 METHODS OF ANALYSIS. 



and pass a stream of oxygen through S, the oxygen stream at D being diminished, 

 but not entirely shut off. When the char has gained a proper temperature, the end 

 nearest A takes fire in the oxygen and the mass glows steadily from A toward D. When 

 the carbon is all consumed, stop the oxygen supply at D, diminish that at S, and 

 gradually lower the temperature during ten minutes, then shut off the burners. Stop 

 the oxygen, and allow the tube to cool somewhat, passing in a slow stream of carbon 

 dioxid. The charring should always proceed slowly, using an excess of oxygen. 

 The time required for one combustion is about one hour. When the tube is suffici- 

 ently cool, remove boats, cool in desiccator, and weigh. The total weight less the 

 weight of the boats equals the ash. For complete analysis of ash proceed as under 

 "III. Inorganic Plant Constituents," page 21, (c), (d), et seq. 



Remove the sodium carbonate containing the volatile products from the tube. 

 Extract with hot water and hydrochloric acid, remove silica, and determine sulphuric 

 and phosphoric acids and chlorin as directed under "III. Inorganic Plant Constitu- 

 ents," pages 22 and 23, paragraphs 4, 5, and 6. 



PREPARATION OF ASH WITHOUT THE USE OP CALCIUM ACETATE. OPTIONAL OFFICIAL 



[Page 21 (b)]. 



Before combustion thoroughly clean the material from all foreign matter. Conduct 

 the combustion at a comparatively low temperature, never employing a full ivd 

 heat (because of the danger of volatilizing alkaline chlorids, etc.) nor a .strong draft 

 of air, lest the lighter part of the ash be carried away. Preferably employ a flat 

 platinum dish in a muffle. With substances rich in silica and alkalis it is better 

 first to char the substances, wash with distilled water to remove soluble salts, then 

 dry and incinerate the residue. Evaporate the aqueous extract and add it to the 

 ash. With substances rich in phosphates, c. g., seeds and animal substances, chj 

 the material, remove salts by acetic acid, decant the acetic solution, wash \vit 

 distilled water, and then complete the combustion. Add the acetic solution am 

 washings to the ash, evaporate to dryness, and gently ignite the whole to decomj 

 the acetates. In whatever way obtained, the whole of the ash should be pulveriz 

 and intimately mixed while still warm, and preserved in a tight, dry bottle for analysis 

 If after incineration the ash has absorbed moisture, dry thoroughly at low redm 

 before bottling. 



