68 METHODS OF ANALYSIS. 



(2) METHOD ii. (Dropped by action in 1907.) 



Use 50 mg of zinc oxid to 25 grams of molasses or 50 grams of sugar. 

 Incorporate thoroughly by adding dilute alcohol and mixing ; dry and ignite as 

 above. Deduct the weight of zinc oxid used from the weight of the ash. 



(3) METHOD in. 



Carbonize the mass at a low heat, dissolve the soluble salts with hot water, 

 burn the residual mass as above, add the solution of soluble salts, and evaporate 

 to dryness at 100 C., ignite gently, cool in a desiccator, and weigh. 



(4) METHOD IV. 



Saturate the sample with sulphuric acid, dry, ignite gently, then burn in a 

 muffle at low redness. Deduct one-tenth of the weight of the ash, then calculate 

 the per cent 



(5) METHOD v. 



Thoroughly mix 5 grams of the material with a somewhat larger weight of 

 pure quartz sand in a platinum dish ; ignite in a muffle at a moderate red heat. 



(6) METHOD vi. 



To avoid the correction of one-tenth, as proposed by Scheibler, and one-fifth, 

 as proposed by Girard and Violette, when sugars are burned with sulphuric 

 acid, Boyer suggests incineration with benzoic acid as giving the real quantity 

 of mineral matter without correction. 



Dissolve 25 grams of the benzoic acid in 100 cc of 90 per cent alcohol. Weigh 

 5 grams of the sugar in a capsule and moisten with 1 cc of water. Heat the 

 capsule slowly to caramelize the sugar without carbonizing it; then add 2 cc 

 of the benzoic acid solution and warm the capsule until all the alcohol is 

 evaporated; raise the temperature until the sugar is converted into carbon. 

 The decomposing benzoic acid produces abundant vapors which render the mass 

 extremely porous, especially if a circular motion be imparted to the capsule. 

 The slow heating is continued until all the benzoic acid is volatilized. The 

 carbon obtained is voluminous and of a brilliant black color. The incineration 

 is accomplished in a muffle at a low red heat. The capsule should be weighed 

 quickly when taken from the desiccator, in order to avoid the absorption of 

 water by the alkaline carbonates. Ammonium benzoate may be employed 

 instead of benzoic acid, and the analyst should previously assure himself that 

 neither the acid nor the ammonium salt leaves a residue on incineration. In 

 addition to giving the mineral matter directly, this method permits the deter- 

 mination of its composition also. 



(b) QUANTITATIVE ANALYSIS OF THE ASH. OFFICIAL. 

 Proceed as directed under " III. Inorganic Plant Constituents," page 21. 

 (c) SOLUBLE AND INSOLUBLE ASH. PROVISIONAL. 



Ash the material according to Method I under the determination of ash, 

 page 67, "3. (a) ;" add water to the ash in the platinum dish, heat nearly to 

 boiling, filter through ash-free filter paper, and wash with hot water until the 

 filtrate and washings amount to about GO cc. Return the filter paper and con- 

 tents to the platinum dish, carefully ignite, and weigh. Compute percentages of 

 water-insoluble ash and water-soluble ash. 



