16 BULLETIN 1122, U. S. DEPAKTMENT OF AGRICULTUEE. 



Table 5. — Absorption of gels. 



Description of sample. 



Absorption per gram 

 of gel. 



Mala- 

 chite 

 green. 



H2O. 



NH3. 



Silica gel: 



Freshly prepared , 



Commercial product , 



Aluminum hydrate gel: 



Freshly prepared 



Chemical Warfare Service product. . 

 Ferric hydrate gel: 



Freshly prepared 



Chemical Warfare Service product. . 

 Aluminum siUcate gel, freshly prepared 



Peat 



Peat, particles below 1 micron 



Average values 



Gram. 



0. 0348 



.0080 



.0889 

 .0735 



.0920 

 .1160 



Gram. 



0. 8658 



.2015 



.6155 

 .3500 



.3090 

 .3106 



.5334 : 1.0888 

 .2736 1 .2907 

 .0982 .2990 



Gram. 



0.1426 



.0966 



.0525 

 .0596 



.0293 

 .0478 

 .0504 

 .1274 

 .0563 



. 1443 . 4812 



.0736 



The different gels, just as the mineral powders, varied widely in 

 their absorptive capacities for malachite green, water, and ammonia. 

 It is significant that on the whole the absorptions of the gels were 

 much greater than those of minerals ground below 1 micron, and 

 were in a class with those of the ultra clays. The average absorption' 

 of all the gels was somewhat below that of the ultra-clay average for 

 malachite green, but higher for water and ammonia. 



A close agreement between the average absorptions of the gels and 

 ultra clays is, of course, not to be expected, since the ultra clays would 

 not be composed of equal amounts of each of these gels. Moreover, 

 the absorptive capacities of synthetic gels vary greatly, according to 

 what appear slight differences in methods of preparation, and they are 

 also profoundly affected by changes generally described as aging. 

 Differences between the absorptive capacities of our gels and those of 

 the chemical company and the Chemical Warfare Service are doubt- 

 less due to differences in both method of preparation and age of 

 product. 



The absorptive data on colloidal mineral powders and synthetic 

 gels are, on the whole, in harmony with the view that the larger part 

 of the colloidal material in soils is not made up of mineral particles 

 but of substances in a gel-like condition. In itself the absorptive 

 data is not conclusive evidence, but it is confirmatory of similar con- 

 clusions arrived at in other investigations. 



GENERAL DISCUSSION. 



The data accumulated in this work indicate that, as a rule, con- 

 siderably less than 5 per cent of the absorptive capacity of a soil is 

 located in the imaltered mineral particles and that 95 per cent or 

 more of the absorption is due to the colloidal material, it is realized 

 that this distribution of the absorptive capacity of a soil, which was 

 determined for malachite green, water, and ammonia gas, might not 

 hold for all substances, although these three substances differ widely 

 in their chemical and physical properties. 



If 95 per cent or more of the absorption of the whole soil is due 

 to the colloidal constituents, the accuracy of absorptive methods for 



