THE ASH CONSTITUENTS OF PLANTS. 213 



during the operation; but the manipulation of it is somewhat difficult, 

 special care being- necessary in collecting- the products of combustion, 

 and, as Berthelot^ states, it })urns only small amounts at a time. Fur- 

 thermore, the apparatus is quite expensive, and necessitates a supply 

 of compressed oxyg-en. The same applies to the modihed apparatus 

 constructed by Mahler and l\v von Hempel and Atwater.*^ 



Grouven^ destroj^ed organic matter by combustion in superheated 

 steam in iron tubes. In this method the sulphur occurring in plants 

 in such compounds as protein, etc., is not oxidized to sulphuric acid, 

 as in the usual process of burning, but is obtained as sulphuretted 

 hydrogen. 



It sometimes happens that the incineration occupies a long time, 

 even in the Shuttleworth and Tucker forms of apparatus exceeding the 

 2 hours which is usualh^ sufficient; for example, when large quantities of 

 fusible salts and especiall}^ alkaline phosphates are present. In such 

 cases the carbon particles are occluded from the action of oxygen of 

 the air; but in burning in an open platinum dish this occurs to a much 

 greater extent, so that the incineration may sometimes require 10 or 12 

 hours and even longer. In such cases the danger from loss of alkaline 

 salts is naturall}' great, increasing as the temperature is raised. 



In order to prevent the enveloping of particles of carbon, due to the 

 fusing of salts, these salts ma}'^ be removed prior to the combustion. 

 In the method of Fresenius,* mentioned above, the charred substance 

 is extracted with water or acetic acid,^ the insoluble portion collected 

 on a filter, dried, and incinerated, and the soluble portion then added, 

 evaporated, and gently incinerated. (See also Reichardt.") This opera- 

 tion requires both time and pains. 



The fusing of the salts may also result in the formation of silicates 

 which are difficult to decompose with hydrocloric acid, as in the case 

 of straw which contains much silicic acid, and is an important point to 

 be observed, as Shuttleworth^ has pointed out. In such case the por- 

 tion of the ash insoluble in hydrochloric acid must be treated with 

 hydrofluoric acid, and the bases contained in that portion estimated 

 separately. 



ADMIXTURES TO FACILITATE INCINERATION. 



To overcome the difficulties of incineration, attempts have been made 

 for manj' years to discover some substance to be added to the mass 



'Ann.Chim. etPhys., 6.ser., 6 (1885), p. 546. 

 • ^ U. S. Dept. Agr., Office of Experiment Stations Bui. 21, p. 123. 

 ='Ztschr. Analyt. Chem., 22 (1883), p. 439. 

 *Jour. Prakt. Chem., 70 (1857), p. 85. 



^Stildeler in Wohler's Mineralanalyse in Beispielen, 1861, 2. ed., p. 188. 

 «Areh. Pliarm.,73 (1853), p. 258. 

 'Jour. LandAV.,47 (1899), p. 173. 



