158 H. 8^ F. J. Warth — On Indian Laterite. 



in the same order as the alumina, whilst the iron increases 

 simultaneously. 



Only in one case, that of No. 13, is there a slight departure from 

 the rule. With the exception of two specimens containing quartz- 

 sand, the quantity of silica is very small. Sample No. 7 contains 

 only 1*14: per cent, of substances other than the oxides of iron and 

 aluminium besides water. The ferric oxide appears to be entirely 

 or nearly entirely anhydrous. If this were not the case we should 

 obtain a regularly increasing series for the molecules of water 

 calculated from the total of the water for one molecule of alumina. 

 Although the table shows that the figures vary, there is no great 

 departure from the average, and, as already remarked, the mean of 

 all the eight specimens implies anhydrous ferric oxide and a mixture 

 of 93 "5 per cent, gibbsite and &-5 per cent, diaspora. 



The identity of these high-level laterites with bauxite is also 

 proved by comparison of their composition with that of other 

 bauxites. Our No. 7 is almost identical with the bauxite from near 

 Giessen with which Dr. Max Bauer compared the specimen from 

 Mahe in the Seychelles. 



Our specimen No. 9 comes very close to an Irish bauxite which 

 has been analysed by Siemens, who found the following, according 

 to Watts' Dictionary of Chemistry : — 



H2O , ... 21-5 



Si02 3-5 



TiOs 2-0 



re263 38-0 



AI2O, 35-0 



100-0 



Treated before the blowpipe, all the specimens of group No. Ill 

 are infusible, the general character of bauxite. Only in the case of 

 No. 10 there were minute fused spots in small number, and No. 12 

 showed also traces of fusion, though they were doubtful. This 

 behaviour of No. 10 and No. 12 is no doubt due to these specimens 

 containing more silica than the others and free quartz-grains. This 

 infusibility serves to distinguish the pure bauxites when mixed with 

 Fe2 O3 from the low-level laterites of the following group, No. IV, 

 which (No. 14 excepted) fused unmistakably. Pure kaolins are 

 also infusible, but if the material is distinctly red from iron the test 

 holds good. 



IV. The fourth group includes low-level laterites arranged in 

 order of free alumina which calculation shows them to contain. 

 The presence of free silica in the form of quartz is proved in 

 all cases, and confirms a principal character of these deposits. 

 Whenever distinct quartz-grains are seen in quantity, some of them 

 being at times rather large, we may be sure that we have a detrital 

 or low-level laterite. Besides the quartz-sand there is, however, 

 generally an even larger proportion of clay.^ This follows from the 



1 On the average 30 per cent, of clay and 20 per cent, of free quartz. 



