
CONDITIONS OF LIGHT, ETC. 

supplied as it is consumed all the living creatures suffer and the water 
deteriorates. Fishes transferred to water deficient in or devoid of air are 
speedily suffocated; but, as elsewhere stated, goldfishes are naturally of 
low vitality and their absorption of oxygen is small, compared with 
some other species whose habitat is running water. This is more or less 
characteristic of all stillwater fishes, notably the Carp family. 
It is not chemically pure water that is required, as this does not exist 
in nature. Some saline,carbonaceous,sulphurous and nitrogenous combina- 
tions are always present, acquired from the atmosphere or from organic 
and inorganic or mineral substances by its absorbing and dissolving prop- 
erties. River, brook, pond, spring, well and rain water all have different 
chemical composition due to these causes, and the proportion and nature of 
the substances present in solution vary with each locality. Rain water 
is usually the purest of the natural waters, containing only slight traces 
of ammonia, carbonic acid, and some inorganic particles taken from the air. 
Pond, brook and river waters usually contain mineral salts, inorganic sub- 
stances, and contaminations of vegetal and animal origin. Spring and well 
waters usually contain mineral salts and other constituents in varying 
quantities and some organic contaminations. 
Substances of a purely mineral nature are less injurious in character 
than those due to animal and vegetal decomposition, to sewage and to 
fungi. The presence of nitrates, nitrites, ammonia, and micro-organisms 
always indicate the oxidation and decomposition of organic matter. Inor- 
ganic and mineral substances are objectionable only when present in 
considerable quantity. 
InorGanic SuBsTANCES PREsENT IN Water. The inorganic sub- 
stances are usually the sulphates, carbonates and chlorates of calcium, 
magnesium, sodium and potassium; also iron, silica, traces of phosphoric 
acid, bromine, iodine and other mineral substances. The presence of 
these combinations with the hydrogen and oxygen affects the quality of the 
water and causes a change known as Hardness, which may be either tem- 
porary or permanent dependent upon the nature of the mineral salts 
present. Soft waters are those which contain the least substances in solu- 
tion; temporary hardness is mainly due to the presence of the carbonates of 
lime and magnesium; and permanent hardness is caused by the sulphates, 
nitrates and chlorates of calcium, magnesium, sodium and potassium. 
The carbonates of lime and magnesium which cause temporary hard- 
ness are soluble only in an excess of carbon dioxide (CO,) and are only 
contained in water in which the CO, is present in such quantity as to hold 
it in solution as bicarbonate of lime and magnesium, as will be seen by 
the formulz:— 
