812 = 546 Ivfixicncc of Chemical Discoveries on 
applied in spring, in accordance with sound scientific principle: 
which teach that nitrate of soda in solution is not retained b 
soils. 
Use of lime and The investigations on the absorption of potash bj variou 
soils have also thrown a new light on the special use ( 
lime and marl on poor sandy soils. Every farmer knows ho^ 
essential lime is for the healthy growth of every kind t 
agricultural produce. On soils destitute of lime, most crop; 
especially green crops, are subject to disease, and consc 
quently roots fail altogether on such land, even if it has bee 
liberally manured with good farmyard manure or guano. Up t 
a certain stage, corn and roots grown under such condition 
appear to thrive well, but as the season advances they sustaii 
a check, and at harvest-time yield a miserable return. The 
remedy for such failures, which are not at all uncommon ii 
localities where poor sandy soils prevail, is a good dose of linn 
or marl, and then, and only then, farmyard manure or guan( 
may be applied to the greatest advantage. Marl or lime alom 
does not suffice for meeting all the requirements of our culti 
vated crops on such poor soils ; and though calcareous mineral 
supply a most necessary element of plant food, and, by actin< 
on the latent stores of food in the soil, produce at first a mos: 
strikingly favourable effect upon vegetation, they soon fail ti 
do this if repeated too often, to the exclusion of other fertllisin' 
matters. On the other hand, the most liberal application oi 
farmyard manure of the best quality never produces so bene- 
ficial and lasting an effect on poor sandy soils as when thej 
have been previously well marled or limed. There are som( 
soils which swallow up manure with, so to speak, an insatiabk 
appetite, without ever feeling the better for the manure — thej 
are appropriately called very hungry. On all such' soils mucl; 
manure is wasted, or the most is not made of it, if previously tc 
the application of farmyard manure, guano, &c., the land has nol 
received a good dose of lime. 
My filtration experiments point out the reason why marl oi 
lime is peculiarly valuable on poor sands. ^ 
Value of lime In passing a solution of sulphate of potash through a pool 
soi!r°^ * sandy soil, I found a weighable quantity of sulphate of ammonia 
in the filtrate, which was not the case when the same solution 
was passed through a marly soil. 
The power of soils to retain ammonia is generally assumed to 
be greater than their power of retaining potash. Here, how- 
ever, an instance is presented to us in which a salt of potash, by 
acting on the ammoniacal combination in a soil, overcomes the 
supposed superior affinity of ammonia. Contrary to all expecta- 
tion, ammonia, in combination with sulphuric acid evidently 
