216 EXPERIMENT STATION RECORD. 



preferred to deduct one-fifth of the ash; and, because of this uncer- 

 tainty, Albert! and Hempel advocate their method of combustion with 

 a known amount of quartz sand, as mentioned above. Hehner ^ has 

 also proposed the addition of sulphuric acid in the combustion of 

 gl3'cerine, using the factor 0.8. 



It is apparent that ash prepared with the addition of sulphuric acid 

 can not be emploj^ed for the later estimation of that acid, or for chlorin, 

 and probably not for phosphoric acid, 



CRUDE ASH — PURE ASH. 



The substance secured by the described methods, whether or not 

 with the addition of some material to assist the incineration, is not 

 the true or pure ash, but is regarded as crude ash. This crude ash is 

 of variable composition, but may contain any residue of carbon which 

 escaped combustion, particles of "sand" from .the soil which adhered 

 to the substance, and more or less carbon dioxid, combined with the 

 alkali bases when other acids, especially phosphoric, are not present in 

 sufficient quantit}^ Carbonic acid is driven otf from calcium carbonate 

 by intense heating, and also from alkali carbonates when fused with 

 silicic acid. To obtain an ash free from carbonic acid Stutzer and 

 Isbert ^ moistened the ash with nitric acid and then glowed again. This 

 is not always applicable, as the chlorin is also partly or wholly vola- 

 tilized. As the carbonic acid in the ash is a variable and uncertain 

 quantity, it is best to estimate the amount present and deduct it from 

 the crude ash. 



The pure ash may be stated to be the crude ash, less the carbon 

 dioxid, unconsumed carbon, and sand. 



DETERMINATION OF CARBON DIOXID. 



The carbon dioxid is usually determined by collecting the liberated 

 gas in a weighed potash bulb. The very complete and satisfactory 

 apparatus described by Fresenius is familiar to all. As this is some- 

 what complicated the writer employs in his laboratory an apparatus 

 similar in part to one described by Vogel,* and which has proved to be 

 very efficient. Shuttleworth avoided transferring the ash from the 

 crucible of his apparatus (p. 211) to a special carbonic acid apparatus 

 by using the crucible itself as a generator, with the stirrer (e) and 

 upper part of the lid {a and <:^) removed. For this purpose he made 

 the joint between the lid and the crucible tight by one or two wide rub- 

 ber bands, and placed a rubber stopper carrying the acid funnel and 

 the evolution tube in the larger opening (h) of the cover. Tucker also 



1 Ztsehr. Analyt. Chem., 28 (1889), p. 363; Jour. Soc. Chem. Ind., 8 (1889), No. 1. 

 ^Ztschr. Physiol. Chem., 12 (1888), p. 78; Ztsehr. Analyt. Chem., 29 (1890), p. 433. 

 'Die Versuchsstation der deutschen Landwirtschaftsgesellschaft. Berlin, 1896, 

 p. 17. 



