July 1, 1897.] S->ipi>lement to the “ Tropical Agriculturist." 
73 
All these crude forms of potash are extensively 
used, and are most suitable for the districts ad- 
jacent to the mines, or to which there exists con- 
venient and cheap transport. Where the cost of 
carriage is considerable, the refined and more con- 
centarted potash salts are more suitable, and if 
account be also taken of the relative expenses of 
cartage and labour, their use is generally found to 
be considerably economical. 
The salts are made of various qualities and are 
chiefly prepared f om carnallit. The method of 
preparation is as follows ; — The carnallit is agi- 
tated with water in large tanks with che result 
that it is decomposed into a magma of finely- 
crystallised muriate of potash and a solution of 
magnesium chloride. The solution retains very 
little muriate of potash at a low temperature, and 
where the proportion of magnesium chloride does 
not exceed three times of the muriate of potash, 
the remainder of the muriate is deposited as 
crystals on further heating and cooling. The fine 
crystals of muriate of potash are further dissolved 
and purified by crystallisation. 
Muriate of potash as sent into the markets and 
used for manure is usually guaranteed to contain 
from 82 to 90 per cent, of muriate, equal to about 
from 50 to 68 per cent, of potash. Two classes of 
sulphate of potash are also sold, viz,, what is 
known as high grade sulphate containing 92 to 98 
per cent, of the sulphate and equal to 50 to 53 of 
potash, and low gade sulphate containing 50 per 
cent, sulphate equal to 27 per cent, potash. 
INSECT PESTS. 
{Continued . ) 
For almost every insect there is a remedy ; the 
question generally is one of applying. There is no 
sovereign remedy for all insects ; for some insects, 
and important ones too, there is no economical 
remedy ; but there are certain general measures 
which if faithfully carried out will largely 
decrease loss from insect attack. The most impor- 
tant of these is clean culture and high culture. 
A great many insect pests lie dormant in culti- 
vated lands at certain seasons finding shelter in 
old stubble, stalk, leaves and other rubbish found 
on the land. Prom such places they come forth 
at other seasons and ready to carry on their des- 
tructive work on vegetation. Obviously, much 
benefit would here result from clean culture. The 
gathering of all rubbish, dead vegetable matter, 
and other refuse, and having it burned or properly 
composed would destroy an immense number of 
these insects. Diseased branches of trees should also 
be burnt and the trunks and branches of standing 
trees kept free of moss, lichens and rough bark, 
beneath which insects or their eggs are harboured. 
Weeds and foreign growth should not be tolerated 
along fences, walls or hedges. Clean culture is 
the stitch in time to save nine. 
High culture is almost equally important in 
warding off insect attack or rather in enabling the 
plant to overcome it. While the plant which is 
weak and sickly through lack of proper cultiva- 
tion or needed fertilizing material in the soil suc- 
cumbs to the attack of insects, the plant which is 
properly cultivated is often able to overcome the 
attack and mature in good condition despite the 
drain upon its vitality. Particularly is this true 
of vegetables. 
Fruit trees kept in vigorous growth may scarce- 
ly appear to be affected by infesting scale insects, 
while trees poorly nourished and uncultivated are 
found losing vitality along its branches when 
attacked to a like extent. Some insects also show 
a decided preference for plants making only a 
feeble growth, and many writers on entomology 
assert that certain insects never attack a plant 
unless it is in an unhealthy condition. The second 
great principle in preventing insect injury is, 
then, keeping the crops well fed and properly cul- 
tivated. 
In addition to the measures already noted, the 
judicious agriculturist will, whenever possible, 
make a judicious rotation of crops to repress 
insect ravages. Many insects, as well as diseases, 
are kept down solely by this means which is eco- 
nomy for other reasons ns well. Such insects 
being capable of subsisting only on a certain plant 
or class of plants, are destroyed by starvation when 
the soil is used for the growth of other plants. 
[In the case of permanent forms of cultivation 
the nearest substitute for a rotation of crops is, ns 
we have previously pointed out in these pages, 
mixed cropping.] 
But many insects cannot be controlled by these 
general methods of culture and need to be dealt 
with by more artificial means. Much attention 
has been paid to such means within the last gene- 
ration, and several very valuable insecticides have 
as a result been brought into common use. It is 
the duty of the agriculturist to be acquainted 
with the best of these insecticides and find out for 
what they are applicable, since an insecticide that 
answers jjerfectly for one insect may be totally 
inadequate for another. 
In general insecticides may be divided into two 
classes : those which kill by contact and those 
which kill by internal poisoning. For the judi- 
cious use of both kinds it is important that we 
should recognise that insects are also divisible into 
tw’o large groups according to their method of 
taking food. One class of insects, which embrace 
locusts, caterpillars and beetles, takes solid food 
hy means of biting jaws, while the other which 
embraces bugs, scale insects, bark lice and the 
like, takes only liquid food imbibed through a 
proboscis. Insects of the first kind can be disposed 
off with tolerable ease by applying poisons such as 
arsenites to their food, while insects of the second 
type are clearly beyond the reach of such poisons. 
Their method of taking food affixes them more or 
less permanently to the surface they are on, and 
through which they suck in their food, so that they 
are vulnerable to ijenetrating insecticides such as 
kerosene emulsion which further close up their 
breathing pores and thus suffocate them. 
SOME CEOP NOTES. 
Onions . — Onions do best upon a light, loamy 
soil, and one that has been kept free from weeds 
by careful cultivation. They can be grown for a 
number of years on the same land if properly fer- 
tilized. Onions thrive well on soils which contain 
much humus, and which is consequently retentive 
of moisture. It is well to have onions preceded 
