last
for several years.

If filtration were required, there would be an extra expenditure for
this, but it will be remarked that as the treated sewage is practically
purified when it leaves the electrical channels, these filters would be
only required for complete clarification, which for most places would
not be a necessity.

The filtering material used could be gradually prepared from the sludge
obtained after electrical treatment, unless it could be more profitably
sold as a manure, and I am not a believer in the value of sewage sludge
in large quantities. This sludge, a waste product, is converted into
_magnetic oxide of iron_, of which I have here two small samples. This
magnetic oxide is a good filtering material, but, like every other
filtering material, it would of course require renewal. There would,
however, always be a supply of the waste product--sewage sludge--on the
spot, and the spent magnetic oxide recarbonized could be used
indefinitely.

The annual cost for dealing with the Salford sewage is estimated at in
round figures L2,500 for coal, labor, maintenance of engines, boilers
and dynamos. To this must be added the consumption of iron and its
replacement, which would have to be written off capital expenditure.

If a colorless effluent were required, absolutely free from suspended
matter, the additional cost is estimated at from L1,200 to L1,500.

* * * * *

LAVENDER AND ITS VARIETIES.

By J. CH. SAWER, F.L.S.

Lavender--technically _Lavandula_. This name is generally considered to
be derived from the word _lavando_, gerund of the verb _lavare_, "to
wash" or "to bathe," and to originate from the ancient Roman custom of
perfuming baths with the flowers of this plant.

The general aspect of the various species which compose this genus of
labiate plants, although presenting very characteristic differences,
merges gradually from one species to another; all are, in their native
habitat, small ligneous undershrubs of from one to two feet in height,
with a thin bark, which detaches itself in scales; the leaves are
linear, persistent, and covered with numerous hairs, which give the
plant a hoary appearance.

The flowers, which are produced on the young shoots, approximate into
terminal simple spikes, which are, in vigorous young plants, branched at
the base and usually naked under the spikes.

As a rule, lavender is a native of the countries bordering on the g