116 
On the Cheiidcal Properties of Soils. 
It is worthy of notice that the sterile sandy soil absorbed as 
much ammonia as tlic calcareous clay, and even rather more than 
the heavy clay soil, thus proving that the property of absorbing 
ammonia is not confined to clay soils, but that it is shared by 
light sandy soils. 
It has been too generally assumed that sandy soils do not possess 
the power of retaining any ammonia ; but the preceding experi- 
ments show unmistakably tliat this opinion is not founded on 
fact. If soluble manuring matters were indeed vci-y readily washed 
out of sandy soils, it is certain top-dressing with nitrate of 
soda, or sulphate of ammonia and other soluble manures, in nine 
cases out of ten, would produce little or no effect upon them ; 
for these top-dressings are usually applied at a period of the year 
when rain falls in abundance, and every facility is afforded 
for the removal of these soluble matters. Experience, how- 
ever, teaches us that such top-dressings are particularly valu- 
able on sandy soils, which could not be the case if these did not 
possess a power ascribed by many persons solely to clay soils. 
Although it is no doubt the case that heavy rains wash into the 
drains useful manuring matters, and that clay soils possess in a 
higher degree the power of retaining fertilizing substances than 
sandy soils, nevertheless we need not, on the approach of a 
heavy thunderstorm, be apprehensive that all the sulphate of 
ammonia or guano which may have been applied to some light 
sandy land only a few days ago, will be entirely washed away. 
Again it may be noticed that the soil taken from the pasture, 
which abounds in vegetable matter, absorbed the least ammonia. 
The question naturally arises. Is the cause of this difference 
due to the presence of organic matter, or to any other pecu- 
liarity in this soil ? I am unable to answer this question 
at present, but think it possible that the presence of a large 
quantity of organic acids in a soil may be unfavourable to the 
retention of ammonia. Future and extended experiments are 
needed to confirm or refute this supposition. In tlie mean time 
I may direct attention to the well-known fact, that on certain old 
pasture land ammoniacal manures produce little effect, whereas 
these manures generally increase the produce of grass in a re- 
markable manner. In all specimens of soil taken from old 
pastures, upon which ammoniacal manures have little or no 
effect, I find a large excess of organic matter. It is just possible 
that this excess of organic matter prevents the retention of 
ammonia by the soil ; but I have no opinion at present as to the 
precise mode in which this is effected. 
I would also notice specially that the soil employed in the third 
experiment was the same heavy clay soil which Mr. Mechi 
kindly sent to me for experimental purposes, and with respect to 
