g considerable
pressure by extra driving at the ends of the rows and then skipping
every other tree in order to keep up the pressure, going over the rows
twice, a very satisfactory pressure can be obtained for trees which
are not too large. The argument for this type of machine, and it is
especially applicable on the general farm, is that it can be used for
other spraying on the farm as well as for the apple orchard,
especially for potatoes and small fruits. It is a comparatively cheap
type of power, particularly when it can be used for several purposes.

The compressed air gas sprayer comes next in point of simplicity and
cost for a power sprayer. Its most economic use is found where
orcharding is carried on extensively enough to pay to compress the air
or gas right in the orchard. This is of course impracticable on the
general farm. Therefore the air or gas must be purchased and shipped
to the farm in steel tubes. This often causes delay at critical times
and is rather expensive. Moreover, the gas is open to the objection of
interfering with the lime-sulphur compound by precipitating some of
the sulphur.

The gasoline engine is the most useful and popular type of power for
the orchard sprayer, as well as for general use on the farm. Many
makes are now so perfected that they give little or no trouble. One
and a half or two horsepower are fully sufficient for spraying, but
most farmers prefer from three to five horsepower in order to be able
to use the engine more for other purposes. The latter power is open to
objection for spraying purposes on account of its weight, as
especially in early spring it is very difficult to haul so heavy a rig
over the soft ground. Such an outfit is also rather expensive.
Standard makes of gasoline engines of sufficient power for spraying
cost from $75.00 to $150.00 according to horsepower and efficiency.
For very large trees, for mature orchards, and for all orchards larger
than four or five acres, the gasoline engine is the best source of
power for spraying, particularly where it can be used for other
purposes on the farm.

A double acting or two cylinder pump is most desirable. If there is
plenty of power a triplex or three cylinder pump is still better. The
requirements of a good pump are: sufficient power for the work desired
of it; strong but not too heavy; fewest possible number of parts
consistent with efficiency; brass parts and valves; and a good sized
air chamber. A number o