Experimental and Applied 245 



Note the correlations of lustre and external appearance with 

 minute structure. 



RAPID-COMBUSTION METHOD. Study method of com- 

 bustion with chromic acid in presence of sulphuric acid (Cross and 

 Bevan, J. Chem. Soc. 53, 889). 



Inorganic or Ash Constituents. Burn specimens of pure cellu- 

 lose and raw materials and estimate ash. Note that the ash con- 

 stitutes an inorganic skeleton of the original. Soak a cotton fabric 

 (muslin) in solutions of ammonium chromate, aluminium acetate, 

 or magnesium acetate ; dry and burn. Note that a coherent ash 

 is obtained preserving the structure of the original fabric. A process 

 of this kind is used in making the hoods for the ' incandescent ' 

 gas burners ; oxides of the rare earth-metals being used for the 

 purpose. 



Take an ordinary filter or blotting paper ; estimate the ash, and 

 a second portion digest in dilute hydrofluoric acid in a lead or 

 platinum vessel. Wash off with distilled water, dry, and determine 

 the ash. It will be found to be considerably reduced, owing to the 

 removal of silica and siliceous compounds. The ash in cellulosic 

 raw materials is much higher than in the bleached celluloses ; 

 notably in the straws. The proportion of silica is exceptionally 

 high. It was frequently affirmed in the older text-books that the 

 rigidity of the straws was due to this constituent, but special culti- 

 vations in absence of silica give a straw of normal appearance 

 and rigidity. The structural properties of these stems are there- 

 fore referable to their 'organic' components. 



Hydration and Dehydration. For a wider discussion of hydra- 

 tion and dehydration types as applied to the elucidation of 

 the special chemistry of the carbohydrates, the student should 

 read a paper by Baeyer, ' Ueber die Wasserentziehung und ihre 

 Bedeutung fur das Pflanzenleben u. die Gahrung' (Berl. Ber. 

 1870, 363); or the translation by Armstrong Q. Chem. Soc. [2], 



9, 330. 



The absorption^ osmotic and capillary phenomena resulting 

 from the interaction of cellulose and aqueous solutions should be 

 carefully studied. Much work remains to be done on this subject. 

 The student should acquaint himself with Pfeffer's methods of 

 determining osmotic pressures, and the bearings of the phenomena 

 of osmosis on the theory of solution. 



