LABORATORY EXPERIMENTS 537 



"National Method'' 



Bentonite Bauxite 



Insoluble 56.80 5.49 



ALOs 17.01 60.00 



Fe.Os 2.87 1.04 



TiO^ 12 .56 



CaO 4.40 



MgO 4.26 



H,0 14.54 32.68 



Soluble. 



100.00 99.77 



A small amount of sulphuric acid in the ground-waters would dissolve 

 out the constituents listed as soluble in the above analysis, and the waters 

 carrying, these salts in solution, on coming to the surface in a region of 

 acid swamp or surface water containing tannic acid, etcetera, would 

 readily deposit them so as to form the bauxite deposits of the Chatta- 

 nooga section. 



Laboratory experiments made on a sulphuric acid solution of bentonite 

 show that on treatment with tannic acid the alumina is precipitated. 

 The experiment was as follows : 



Samples of bentonite were prepared by treating with 25 per cent sul- 

 phuric acid, boiled 3 to 4 hours with reflux condenser, filtered; filtrate 

 evaporated about to dryness, taken up in water, boiled, and filtered. 



Samples were all made up to 500 cubic centimeters and contained 

 about 1 per cent free sulphuric acid. 



The tannic acid used was "tannic acid — pure,'' from Eimer and 

 Amend, N'ew York. The formula is Ci4HioO;). This is a monobasic 

 organic acid; may also be written H.Ci^HgOg or C13H9O7.COOH. 



Sample number 1 contains sulphuric acid soluble matter from 25 

 grams bentonite plus 5 grams tannic acid (dissolved in a little water) 

 and the whole diluted to 500 cubic centimeters (5 per cent bentonite 

 plus 1 per cent tannic acid). 



Sample number 2 : 5 per cent bentonite plus 0.5 per cent tannic acid. 



Sample nimiber 3 : 5 per cent bentonite plus 0.1 per cent tannic acid. 



Sample number 4 : 2 per cent bentonite plus 1.0 per cent tannic acid. 



Sample number 5 : 2 per cent bentonite plus 0.5 per cent tannic acid. 



Sample number 6 : 2 per cent bentonite plus 0.1 per cent tannic acid. 



Sample number 7 : 1 per cent bentonite plus 1.0 per cent tannic acid. 



Sample number 8: 1 per cent bentonite plus 0.5 per cent tannic acid. 



Sample number 9 : 1 per cent betnonite plus 0.1 per cent tannic acid. 



The above samples were put up in 500-cubic-centimeter flasks, stop- 



