§ 7. ESTIMATION OF ASH. 7 



because these solvents do not penetrate into the cells, but only- 

 dissolve that which is adhering to the external surfaces of the 

 object. It must be admitted that it is often very difficult to 

 reduce a vegetable substance to an impalpable powder, but the 

 necessity of sparing no trouble in this respect must be most 

 strongly urged. It may sometimes be expedient to dry very 

 hard substances, such as seeds, etc., at 100° to 110° before powder- 

 ing them. Coffee-seeds may thus be reduced to quite a fine 

 powder, especially if triturated in an agate mortar with a known 

 quantity of powdered glass or sharp sand (that has been pre- 

 viously treated with hydrochloric acid). Somewhat hard sub- 

 stances may occasionally be grated upon a fine grater with 

 advantage, and then powdered as above. Tough material, too, 

 and such as is to be examined in the fresh state, may be generally 

 prepared in this way. In working with substances containing 

 much fixed oil it is sometimes expedient to dry the residue 

 after the first extraction with petroleum spirit, etc., powder it 

 again and repeat the extraction. 



§ 7. Estimation of Ash. — With regard to the total ash, which is 

 usually estimated in plant analysis, reference may be made in the 

 majority of cases to the generally known methods of procedure. 

 For vegetable substances that are very difficult to incinerate, it is 

 advisable, after carbonization, to cool, powder as finely as possible, 

 and continue the heating, placing a cylindrical tube vertically 

 above the platinum dish, so as to create a cui'rent of air. Or the 

 incineration may be conducted in a Hempel's jacket with access 

 of air. If easily fusible salts are present and prevent complete 

 incineration, the admixture of about an equal weight of nitrate of 

 ammonium with the cooled mass, and repeated ignition, may render 

 good service. Or the carbonized mass may be mixed with a weighed 

 quantity of oxide of iron, and the incineration continued. ^ 



After weighing the ash the quantity of carbonic acid present in 

 it is to be determined and deducted from the total weight. The 

 carbonic acid is simply a part of the organic matter, the rest 

 of which has been burnt off, and is to be determined in other 

 ways. It is also desirable to test the ash for sand, and finally, 

 if a complete analysis is not required, to estimate at least 

 the total quantity of phosphoric and sulphuric acid and potash. 

 (See also § 82). 



1 Compare also Bornträger, Zeitschr. f. anal. Chemie, B. xvii. p. 440 (1878). 



