88 TRANSACTIONS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE 
In Xo. 7 there is still a diminution in the free ammonia, and a 
most decided drop in the albumenoid ammonia, sho™g the highly 
beneficial results of filtration. At the same time allo'w me to most 
strongly emphasise the fact that the presence of the amount '015 of 
albumenoid ammonia in ever}' 100,000 parts of the water just before 
filtration, taken along vuth the free ammonia found farther up the 
river, and the nitrogen as nitrates and nitrites just before filtration, is 
a distinct proof of contamination. 
Professor Wankl}'n says that ‘‘if the amount of albumenoid ammo¬ 
nia amounts to ‘002 parts per 100,000 then the water belongs to a class 
of ven'pure water. When the albumenoid ammonia amounts to '005 
parts per 100,000 then the proportion of free ammonia becomes an 
element m the calculation.” hen the free ammonia exceeds 008 
parts per 100,000 it is often due to the fermentation 01 urea into car 
bonate of ammonia, and shows the presence 01 sewage contamination. 
And he says—I should be inclined to look vdth suspicion on a water 
yielding a considerable quantity of free ammonia along ^^dth more 
than -005 parts of albumenoid ammonia per 100,000 parts. Free 
ammonia, however, being absent, or very small, a water should not 
be condenmed unless the albumenoid ammonia reaches something like 
'01 parts per 100,000. Albumenoid ammonia abo'se tnis begins to 
be a ver}’ suspicious sign, and over "015 parts per ioo,coo ought to 
condemn a water absolutely. The absence 01 chlorine, or an amount 
of it which does not exceed i’4 parts per 100,000, is a sign that the 
organic impurity is of vegetable 7‘athcr tlw.n 01 aifimal origin , but it 
would be a mistake to allow water highly contammated ^vith vege¬ 
table matter to be taken for domestic use. Xow, from this table 
you vrill, we think, clearly understand that the water oi the rher at 
Perth before filtration is contaminated, and decidedly objectionable 
for drinking purposes, and hence the absolute necessit} for caretul 
filtration, and vou ■will also be led to inquire whether filtration renders 
the water sufficiently pure at all times to be called a perfectly mnocu- 
ous water for domestic and dietetic purposes. 
4. The amount of lime giAng rise to the hardness in the water is 
very small all the way down to Perth, and this, along with the absence 
of an excessive quantity of organic matter, shows the water to be ad¬ 
mirably adapted for the important mdustries of dyemg and bleaching, 
for which Perth and its tycinity have long been famous. The water 
is also most suitable for washing purposes, and for use m steam 
boilers. This is well shown by comparison with the London water 
supplv, which has about 25 degrees of hardness, and is most unsuit¬ 
able for dyeing or bleaching purposes. 
q. The only other thing to note here is that in our second table, 
the temperature of the air and water is very nearly alike; but, as a 
