THE TROPICAL 
AGRICULTURIST. [July i, 1881, 
decay of further portions, and thus assists in bringing 
them into a form available for plant food. But if the 
lime has been long exposed to the air before spreading 
upon the land, this valuable property is entirely 
lost. 
On the other hand, it is not wise to spread the lime 
before it has become hydrated, as, supposing there are 
compounds of ammonia in the soil, the lime seizes upon 
the acids of these compounds and sets free the ammo- 
nia, which rapidly escapes into the air ; besides, instead 
of causing the decomposition of organic matter in a 
favourable manner, it would take away its water, dry 
it up, and tend to carbonise it and render it useless. 
The lime should really be shot in heaps in convenient 
places, and slacked in the same way as the bricklayer 
slacks his litne for making mortar ; and as soon as it 
has been mixed up -with sufficient water it should be 
covered up with earth, to keep the carbonic acid of 
the atmosphere away from it, After allowing it time 
to slack, it should be quickly spread upon 
the land, and harrowed in immediately. It should 
not be ploughed in, as it is well known that 
lime rapidly sinks into the soil, so that it 
only requires a superficial covering of earth, just suffici- 
ent to keep the air form readily reaching it. Lime 
applied in this way also assists in decomposing the 
rocky materials existing in soils, thereby liberating 
the alkalies and aiding the formation of nitre, which 
is of such well-known value as manure. In this form 
also, it neutralises free acids, and also renders land 
light and porous — sometimes, in fact, too porous for 
wheat and other crops requiring compact soils for their 
perfect development. In cases of this kind, the roller 
will generally be a sufficient remedy, as it is only the 
mechanical action of the lime, and not its chemical 
composition, that has caused the difficulty. Indeed, 
it is impossible to injure heavy land by the applica- 
tion of lime in any quantity, provided it is properly 
slacked and applied in its hydrated form. With lighter 
soils it is different, and if too much lime in its 
caustic form be applied to these, it quickly decomposes 
the small available quantity of organic matter which 
such soils contain, and uses it up in one short season. 
No doubt it whips up the immediate crop, but it does 
so at the expense of the future. To soils of this 
kind, sulphate may be applied as a source of lime in 
large quantities, without the slightest fear of injury, 
and, indeed, with the most beneficial results ; but of 
this I will speak later on. With regard to the limes 
manufactured from chalk, it is believed by farmers 
that those made from the lower grey chalk give better 
results than the purer and whiter limes from the upper 
beds, and many who have had long agricultural ex- 
perience willingly give a much higher price for the 
grey than the white. It might seem strange at first 
sight that a lime containing alumina and other impurities 
should be more esteemed for agricultural purposes than 
the purer article but it is no doubt these thatreally 
enhance its value. Professor Way discovered that the 
fertility of soils largely depended upon the presence 
of certain forms of double silicates of lime and alumina, 
potash and alumina, and ammonia and alumina ; and 
it is rnore than probable that these clay-containing 
grey limes hold their silica in the form of a double 
silicate of lime and alumina, and possibly that very 
form of double silicate Professor Way found to be so 
valuable. The value of this double silicate of lime 
depends upon its property of passing into the double 
silicates of potash and ammonia in presence of these 
bases respectively, and so forming compounds easily 
soluble in the carbonic acid contained in rain water, 
and in the weak organic acids with which they come 
in contact. 
Before leaving the consideration of this simple form 
of lime, it may be well to mention that if it is mixed 
with perfectly fresh dang no harm will happen ; but 
if decomposition has commenced ammonia has been 
formed, and, no matter what from it may have taken 
— whether carbonate, humate, ulmate, &c. — the lime 
will inevitably seize upon the acid, and set the 
ammonia free to escape into the atmosphere. 
Phosphate of lime, such as is found in bones, copro- 
lites, and other natural substances, is composed of lime 
168 parts and dry phosphoric acid 142 parts, by weight. 
In this form it is a perfectly insoluble substance, the 
bone production being, however, more readily changed 
to a soluble form than the mineral. When the dairy 
pastures, especially of Cheshire, became exhausted 
through furnishing for a length of time the phosphites 
to build up the bones of the young stock raised on them, 
and also those carried away by the milk which was 
sold for human consumption, it was discovered that 
an application of bones, either fermented or ground more 
or less finely, produced excellent results, often entirely 
renovating land which had become almost useless. 
These effects, however, were produced slowly, as bones 
in their natural form cannot act as plant food. Whether 
they are heaped with earthy matter, or whether as 
bone dust they are applied to the soil, the subsequent 
action in either case is similar. The organic portion 
is fermented and decomposed, and the phosphate of lime 
is acted upon in the following manner. Carbonic acid 
is perhaps the most obliging acid known. It is turned 
out of its combination with all basic substances by the 
direct application of any other acid under the eun ; but 
in the case under consideration it has a slow but effective 
revenge. It has such an affinity for lime that, under 
such conditions as it finds in the soil or compost heap, 
it gradually takes away one-third of the lime from the 
insoluble phosphate, forming with it chalk, and leaving 
the remaining two-thirds behind. These two-thirds are 
now in combination with the original quantity of phos- 
phoric acid together with some water which has also 
been admitted, and the substance now formed is bi- 
caleic phosphate of lime, its composition by weight 
being as follows : Lime, 112 ; phosphoric acid, 142 ; 
and water, 18 Here, it will be seen, the carbonic acid 
has taken away 56 parts of the lime to form chalk, 
whilst 18 parts of water have replaced the 56 parts of 
lime taken away. The new body is fairly soluble, and 
is probably the very best form of phosphate of lime 
to add to the land. It is able to furnish plant food 
slowly but surely ; it is sufficiently soluble, but 
it is not rapidly used up, and it feeds the plant 
through all stages of its growth. Agriculturists 
were perfectly satisfied with fermented and ground 
bones, until it was discovered and made known 
by Liebig that, if bones wore subjected to treatment 
. with sulphuric acid, a much more soluble, and, it was. 
supposed, better manure, was obtained. 
This discovery was immediately utilised by a well- 
known manure manufacturer, and so great 'was his 
success that other large makers sprung into exisience 
one after another, until the industry has now become 
of enormous dimensions. Now many hundreds of 
thousands of tous of pyrites are imported annually, 
for the manufacture of the sulphuric acid* required to 
make this manure. These are shipped to the Thames 
or the Tyne, &c, where the manure maker burns 
out the sulphur and oxidises it to sulphuric acid, 
after which the copper is extracted, and the residue 
then passed on into other hands for the manufacture 
of iron. The principle involved in the production of 
superphosphate is as follows. After the gelatine has 
been extracted from the bones, they are treated w ith 
sulphuric acid, in proportion of 1961b. of pure acid to 
3101b. of bone phosphate. As before stated, this 
bone phosphate is composed by weight of 168 parts 
ol lime, and 142 parts of dry phosphoric acid. 
The sulphuric acid now acts in precisely the same 
way that the carbonic acid in the soil acted under 
the older system, but it does exactly twice the work 
of the latter, and does it rapidly, instead of by a 
tedious process. Instead of taking away 56 parts of 
