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 saIine,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 (CO2) and are only 

 contained in water in which the CO2 is present in such quantity as to hold 

 it in solution as bicarbonate of lime and magnesium, as will be seen by 

 the formulas: — 



172 



