Power of Soils to absorb Bfanure. 



133 



silicate of alumina and ammonia cannot be decomposed bj any 

 neutral salt of the other alkalies. 



I may mention here a circumstance, which at the time appeared 

 very curious, but is now readily accounted for. In the early in- 

 vestigation on filtration of manures, an experiment was made of 

 passing flax-water through a bed of white clay. As usual, a 

 great absorption of the different bases occurred, but the result 

 differed somewhat from those which had preceded it. I give the 

 account of it as it was reported in my first paper (vol. xi., p. 369) : 

 — " It will be observed that the quantities of lime and sulphuric 

 acid in the resulting, are (v/ithin errors of experiment) the same as 

 in the original, liquid. The quantity of chlorine is also as nearly 

 as possible the same in both liquids, but in the original flax-water 

 part of it was in combination with potassium, which, after treat- 

 ment with clay, has been replaced by sodium. We have here 

 two results which were unexpected — the first, that the quantity of 

 lime should not be increased, which seems opposed to the prin- 

 ciple before laid down, that lime replaces in the liquid the potash 

 and magnesia previously combined with sulphuric and muriatic 

 acids ; the second peculiarity is the existence in the resulting 

 solution of much more soda than existed in the flax- water itself. 

 This soda can only have been derived from the clay, which we 

 find from the analysis contains this alkali in considerable quan- 

 tity. It would seem, therefore, that in the present instance soda, 

 and not lime, had acted the part of the substituting base. It is 

 useless at this stage of the investigation to attempt to reconcile 

 these apparent inconsistencies." 



These apparent inconsistencies can, however, now be satis- 

 factorily reconciled ; for it is plain that wherever a sufficient 

 quantity of any base high in the above list exists in a soil, the 

 substitution will be confined principally or entirely to it — the 

 white clay in question contained a large quantity of soda silicate, 

 which necessarily took an active part in the absorption of the 

 ingredients of the flax water. 



Nothing indeed could more clearly prove the advantage of the 

 course which has been pursued, namely, that of instituting an 

 examination of these compounds in the abstract form rather than 

 confining the inquiry to the soils themselves. Incidentally also 

 we find in this circumstance a very strong ground of belief that 

 the substances now formed and studied out of the soil are really 

 those that in it are the active cause of the absorptive property, 

 since the results so closely correspond with what they should be, 

 according to the explanation proposed. 



In glancing again at this list, it will be seen that all the silicates, 

 without exception, are capable of absorbing ammonia. This is 

 very important, inasmuch as it exhibits so very certain a provision 



