Composition and Practical Value of Native Guano. 419 
The examination of sewage purified by the ABC and other 
precipitating processes has shown me that, with the exercise of 
a mo<)erate amount of care, the whole of the suspended matter 
may be removed, and the most filthy looking and disagreable 
smelling sewage be rendered clear as water, and so far deodorized 
as to possess but a faint sewage smell. Left in contact with air 
for a short period, the faint sewage smell of the clarified sewage 
entirely disappears, nor does it return, however long the liquid 
may be kept. But if the purified sewage is placed in a 
stoppered bottle, the original foul smell of raw sewage soon 
returns, showing that clarified sewage contains soluble organic 
matters which enter into putrefaction unless they are brought 
into contact with atmospheric oxygen, and thereby converted 
into inodorous and harmless soluble compounds. 
Whilst it appears to me decidedly objectionable to pour large 
quantities of even the most perfectly purified sewage into a 
watercourse running very sluggishly, and containing but little 
water, and consequently an insufficient supply of air to effect 
the oxydation of the soluble organic impurities present in such 
sewage, no fear need, I think, be entertained that the discharge 
of the moderate amount of clarified sewage of a small town into 
a large bulk of quick running water will poison the water, or 
create the least nuisance. 
It is well, however, to bear in mind that neither the ABC 
process, nor any other known precipitating plan, removes in any 
appreciable degree the ammoniacal salts and other soluble saline 
compounds upon which the fertilising value of sewage mainly 
depends, and that, speaking generally, only one-eighth of the 
fertilising value of sewage resides in the suspended impurities 
which are removed by precipitation, and seven-eighths of its value 
is due to the matters held in solution. 
All who are practically acquainted with sewage irrigation are 
fully aware of the obstacles which the suspended matter in raw 
sewage interposes to successful irrigation. Clarification by any 
good precipitating plan, whilst it only removes a small portion 
of fertilising matter from sewa<re, greatly improves its suitability 
for irrigating purposes. Experienced sewage farmers, I believe, 
will bear me out in maintaining that sewage perfectly clarified 
has a greater practical value than it has in a raw state with 
all the suspended filth in it. 
Although sewage purified by the ABC process, or any other 
equally efficacious or better plan, under some conditions, may be 
poured into running water without risk of creating a nuisance or 
spoiling the water for the purposes for which it is adapted, 
it appears to me a great pity to waste this liquid, which is 
more valuable, because better adapted for irrigation purposes, 
