THE ASH CONSTITUENTS OF PLANTS. 209 



fore, it has been recommended by Baimiert, Councler/ and von 

 Schroder and Reu^s^ to employ an alcohol lamp in exact determinations 

 of the sulphur content of plants, as, for example, in studyino- the injury 

 to forest trees caused ])y the sulphur in the gases given off by smelters. 

 In such cases the Berzelius alcohol lamp or one of similar construction 

 should be employed. 



AVhen the incineration is carried on in a platinum dish care should 

 be taken to bring the glowing substance into contact with the air, either 

 by frequent stirring, or by suspending a glass tube, for example an 

 ordinary lamp chimney, above the dish to increase the draft. ^ There 

 is always a danger, too, that the substance in the bottom of the dish 

 may be heated tjoo high, while the top poi-tion will not be heated enough, 

 and thus the incineration be uneven. In order that the upper portions 

 of the substance may be properl}^ incinerated the heat must be applied 

 from above, and this is accomplished most simply by la^'ing a platinum 

 cover loosely over the dish, which holds the heat in and reflects it upon 

 the substance.* This is accomplished in the method of the Association 

 of Official Agricultural Chemists^ by the use of a nuiffle. 



If care is not exercised and a too high degree of heat is applied, inac- 

 curacies may follow, due to the volatilization of the alkalis as well as 

 some of the phosphoric " and sulphuric acids, or other errors, as the 

 fusing together of the ash inclosing carbon and the formation of sili- 

 cates which are difficult to decompose. 



To avoid the volatilization of sulphuric acid or sulphur in other fo-ms 

 various methods have been employed. For example, W. Mayer ' found 

 0.464 per cent of SO3 in wheat when incinerated with potash and salt- 

 peter, and only 0.04 to 0.06 per cent when incinerated in the ordinary 

 manner. Ulbricht^ treated clover leaves by heating in nitric acid and 

 drj^ing and then incinerating with saltpeter and potassium carbonate. 

 With this treatment 1.476 per cent of SO3 was found, while a portion 



» Landw. Vers. Stat., 27 (1882) , p. 376. 



^ Die Bescliiidigung der Vegetation durch Ranch. Berlin, 1883, ji. 133. 



' F. Schulze in Fresenius' Anleitung zur quantitativen Analyse. 6. ed., vol. 2, p. 639. 



* Schloesing, Contribution a I'etude de la chimie agricole, p. 225, in Fremy's Ency- 

 clopedie chiniique, vol. 10. Paris, 1885. 



^U. S. Dept. Agr., Division of Chemistry Bui. 46. 



*Erdinann (Ann. Chem. u. Pharm., 54 (1845), p. 353) and Strecker (Ann. Chem. 

 u. Pharm., 73 (1850), p. 346) have called attention to this point; while according to 

 Lechartier (Compt. Rend. Acad. Sci. Paris, 109 (1889), p. 727) scarcely any phos- 

 phoric acid volatilizes, though some sulphuric acid may be driven off. See also 

 Weber (Ann. Phys. u. Chem. [Poggendorff ] , 81 (1850), p. 402). 



^Ann. Chem. u. Pharm., 101 (1857), pp. 129-154. 



8 Landw. Vers. Stat., 3 (1861), p. 249. 



