208 EXPERIMENT STATION RECORD. 



others, has pointed out. This is recognized by handbooks of analyt- 

 ical chemistry, such as Fresenius's, for example, which treat the sub- 

 ject of ash analysis at considerable leng'th. 



PREPARATION OF THE ASH. 



The principle of ash determination is very simple, and while in the 

 case of some materials the incineration is easily made, in the case of 

 many others great difficulties are presented which may cause quite large 

 errors. The following points should be especially noted: (1) The 

 incineration must be complete or nearly so, and no carbon should 

 remain. (2) None of the ash elements should be volatilized, this pre- 

 caution applying especially to potash and soda, phosphoric acid, sul- 

 phuric acid, and chlorin. (3) Further, it should be remembered that 

 elements which occur only in part as highly oxidized inorganic acids 

 but in other forms as well, as, for example, sulphur in proteids or 

 phosphorus as glycerine-phosphoric acid in lecithin, are onl}^ present 

 in the completely incinerated ash in the form of acids (sulphuric and 

 phosphoric acids). 



In case it is desirable to know how much sulphuric acid, as such, is 

 in the original substance before incinerating, it is extracted with dilute 

 hydrochloric or nitric acid in the cold or with slight heat, and the sul- 

 phuric acid precipitated with barium chlorid. ^ 



For the combustion of the organic matter various methods have been 

 described since the time of de Saussure, some simple and others more 

 complicated, only a few of which can be noted. De Saussure^ wrote: 

 "The . . . plants are burned on a large sheet of iron, and the residue 

 incinerated in a crucible at a dark red heat until the carbon particles 

 can not be burned further." He first burned the substance in large 

 quantity on an iron plate to reduce the volume, and then completed 

 the incineration in a crucible (probabl}'^ of clay). This method is 

 practiced at the present day when a large quantitj^ of ash is desired, 

 and when a sufficiently large platinum crucible is not available one of 

 fire clay is used, the charred mass being transferred to a smaller plat- 

 inum crucible for completing the operation. 



The ordinary platinum vessels, both crucibles and dishes, permit the 

 free access of a current of air. The crucible was formerly heated over 

 a charcoal fire or an alcohol lamp. In the incineration over a coal-gas 

 flame or oven, as is now commonly done, there is the danger that some 

 of the sulphur of the gas may be oxidized and unite with the bases of 

 the ash, thereby causing an error in the sulphuric-acid content. There- 



^ J. Konig, Unteruschung landwirthschaftlich und gewerblich wichtiger Stoffe. Ber- 

 lin: P. Parey, 1898, 2. ed., p. 192. 



2 Chemische Untersuchungen iiber die Vegetation von Theodore de Saussure, 1804. 

 Translated by A. Wieler. Leipsic: Engelmann, 1890, pt. 2, p. 80. 



