46 
ingredients used in precipitation—alum, blood, clay. The whole 
precipitant is made up about as follows, viz :— 
Alc as= ae) lo. CUROO pants 
Bilowde ane 2 Beal 1S Laws 
laa RG? eas) 2.00 Hea 
Manganate of Potash . LON es 
Burnt Ghigo AMT eP CNA 4y 
Chloride of Sodium oa, Ghee OMS 
Animal Charcoal.g 7.3.5 15) %; 
Vegetable Charcoal ... 20 ,, 
Magnesian Limestone... NN. 
The animal and vegetable charcoal do not need to be used 
together, one only will answer all purposes. The animal charcoal, 
blood, and clay are dissolved together in sufficient liquid (gener- 
ally sewage) and flow through a small channel which discharges 
into the sewer a little above the tanks, which are three in number. 
The alum is dissolved in a separate vat in sufficient liquid (sewage) 
and discharges (by another channel) into the sewer a few feet 
below the point of discharge of the first channel. The whole 
ingredients flow with the sewage through a mixing channel, and 
discharge into the first of the three tanks, in which the greatest 
precipitation takes place, on the next or middle and so on into 
the third tank. The effluent is not filtered, but flows directly 
into a stream. It is almost colourless, having only a faint yellow 
tinge, in great contrast to the dark sewage seen on approaching 
the works. There is no bad smell arising from these works. 
The sludge is dried, ground, packed in bags, and sold as ‘‘ Native 
guano,” at 70s. per ton at the works. It is said to possess a high 
value as a fertiliser. 
The lime process is the oldest method of purifying sewage by 
precipitation before the public. It is in use in our own town in 
its best known form, viz :—General Scott’s process, which is as 
follows :—‘‘ A small proportion of lime is mixed with sufficient 
liquid (water or sewage), and is pumped through a small pipe to 
a point above the tanks, where it enters the sewer and flows 
with the sewage down what is known as a “salmon ladder; ” in 
this the lime and sewage are mixed and through it are conveyed 
to the tanks which are in two sets of three. In these tanks 
precipitation takes place, the effluent, which is fairly clear, being 
turned into (in Burnley) the Pendle water. The sludge is pumped 
into small settling tanks, in which it stands for about seven days 
(longer in wet weather), it is afterwards passed through a pug- 
mill, then spread on a large drying floor in cakes. These, when 
quite dry are placed in a kiln along with about an equal quantity 
of coke, and are burnt to a clinker, which is ground into cement, 
and which will bear a tensile strain of from 250 to 350 lbs. to 
