
CONDITIONS OF LIGHT, ETC, 

CaCo; -- H.-CO, Gace, CO, + H, Ca EPG. yi, 
( Carbonate ) ( Carbon artociah 
of lime PIPE ( Structural formula ) ( Condensed formula ) 
or MgCO, + H,CO, = MgCO, + CO, + H,O = Mg(HCO,). 
aeremee a unoanae 
; ( Structural formula ) ( Condensed formula ) 
The hardness produced by these causes is called temporary because it can 
be removed by boiling the water, the bicarbonates being thereby changed 
into the original simple carbonates by driving off the carbonic acid gas 
and precipitating the carbonates in insoluble form:— 
Ca Ee; — CacO.-- H,O.-- CO; 
( Bica eee) Carbonate ) ( i ater) Carbon ) 
of lime ( of lime . ies 
, 
The sulphates, nitrates and chlorates which cause permanent hardness are 
-not affected by boiling and are retained by the water. 
Water ANALyses. Some years past the author had occasion to 
make a number of analyses of Schuylkill and Croton river waters for 
manufacturing purposes, and collected considerable data which is of 
interest. 
For drinking -and manufacturing purposes the analytical deter- 
minations are usually ten in number, and these are, in their respective 
order, Total Solids, Mineral matter, Organic and Volatile matter, Organic 
Carbon, Ammonia both free and albuminoid, Nitrogen, in any or all 
the forms of nitrates and nitrites, combined nitrogen and organic nitro- 
gen, Chlorine and Metallic salts; also the amount of Oxygen required to 
oxidize the water, usually by the permanganate of potassium color test, the 
degree of hardness, and a microscope examination. ‘These are more than 
are required for the examination of aquarium water. 
It is of interest to note that an analysis of the water of a balanced 
aquarium, which had not been changed for eight months, made for Mr. 
Mark Samuels by Prof. Leeds, should be of such remarkable purity. As 
may be naturally supposed the aquarium water contained the greatest 
proportion of solids, mineral matter, chlorine and the highest degree of 
hardness, due to easy explained causes. Rain water is the lowest in all of 
these constituents, while the very highest are Deep well and Spring waters. 
In point of purity as toammonia, the aquarium water is as low as many 
of the city supply waters; and as to nitrogen, the proportion of nitrites is 
lower than Schuylkill water and the nitrates but two-tenths higher. The 
high percentage of chlorine is to be explained by the probable addition of 
table salt, from time to time, in the aquarium, and from the animal waste. 
All natural waters are chemically impure, though they may be per- 
fectly clear and free from suspended particles. They contain substances 
in solution, due to water being a natural universal solvent, which more 
than any other liquid dissolves and takes up solids, liquids and gaseous 
173 
