346 Absorption of Potash by Soils of knoicn Composition. 
localities where poor sandy soils prevail, is a good dose of lime 
or marl, and then, and only then, farmyard manure or guano 
may be applied to the greatest advantage. Marl or lime alone 
does not suffice for meeting all the requirements of our cultivated 
crops on such poor sands, and though calcareous minerals 
supply a most necessary element of plant-food, and by acting on 
the latent stores of food in the soil, produce at first a most strik- 
ingly favourable effect upon vegetation, they soon fail to produce 
the desired effect if repeated too often, to the exclusion of other 
fertilizing matters. On the other hand, the most liberal applica- 
tion of farmyard manure of the best quality never produces so 
beneficial and lasting an effect on poor sandy soils as when they 
have been previously well marled or limed. On such land no 
doubt the proverb holds good : — 
" Lime and marl without manure 
Only make the farmer poor." 
But at the same time I have a strong impression that on such 
land manure, without lime or marl, does not help much towards 
paying the rent. There are some soils which swallow up 
manure, with, so to speak, no satiable appetite, without ever 
feeling the better for the manure ; they are appropriately called 
very hungry. On all such soils I have no hesitation in saying 
much manure is wasted, or the most is not made of it, if previously 
to the application of farmyard-manure, guano, &c., the land has 
not received a good dose of marl or lime. 
My recent filtration experiments point out the reason why marl 
or lime is peculiarly valuable on poor sands. It is not merely 
by supplying in a direct manner a deficient element of nutrition 
that lime acts so beneficially on such soils, 'but because it pre- 
serves in the soil the more valuable fertilizing matters, which, 
like salts of potash or ammonia, rapidly filter through sandy 
soils, unless a sufficient quantity of marl or lime has been pre- 
viously applied to the land. By these means the bases of the 
more valuable saline soluble constituents of rotten dung or of 
guano are retained in the soil, whilst the acids filter through it 
in combination with lime, a constituent which is, comparatively 
speaking, inexpensive. 
4th Series. — Experiments with a Solution of Chloride 
of Potassium. 
Experiment No. 1. — On Calcareous Soil. 
3500 grains of calcareous soil * were mixed with a solution 
of 52 91 grains of pure chloride of potassium in 4 decigallons 
For analysis see p. 334. 
