The Sanitary Value of the 



that its removal is well nigh impossible, but such matter may gener- 

 ally be disregarded as unimportant from a hygienic point of view. The 

 dissolved constituents consist both of gaseous and solid substances. 

 The former may be the atmospheric gases only and aside from 

 the indications which the quantities of nitrogen and oxygen and 

 the ratio between them are thought by some to afford as to the 

 amounts of organic matter which are undergoing oxidation their 

 quantity is of little importance. Sulphuretted hydrogen and other 

 noxious gases may indeed be present as the result of putrefactive 

 changes or peculiar conditions, and the recognition of such con- 

 stituents may become a matter of importance, not because they are in 

 themselves capable of producing disease iu the quantities which may 

 be present in water, but because their existence throws light upon the 

 chemical changes which are taking place. 



The dissolved solid constituents of potable waters are both inorganic 

 and organic, the latter either of animal or vegetable origin. Up to 

 twenty years ago the ordinary method of quantitative determination 

 was to evaporate a definite quantity of the water to dryness in a plati- 

 num dish, weigh the residue, calculate the percentage of total solids, 

 and then determine the organic or volatile matter by the loss result- 

 ing from the ignition of the total solid residue, due correction being 

 made for the loss of carbonic acid. A complete analysis was then 

 usually made of trte mineral constituents, but as the precise amounts 

 of these are of little importance and as the method described for 

 determining the organic matter afforded no clue to its nature and 

 was too inexact to be of value even in ascertaining the amount with 

 accuracy, it may be readily seen that the results thus obtained were of 

 little or no sanitary value. In speaking of the exact determination of 

 the mineral constituents as unimportant reference wa3 had to the 

 lime, magnesia, iron and other salts usually occurring in all natural 

 waters save rain water, and not to the chlorine, phosphoric acid, 

 nitrates and nitrites which are important but which formerly received 

 less attention than at present. For manufacturing purposes of course 

 a soft water is generally to be preferred. Hard waters, however, act 

 upon lead less than soft ones, while on the other hand they occasion 

 a waste of soap and are not desirable for culinary purposes, but these 

 are incidental questions, and it cannot be said to be proven that the 

 amount of mineral matter in potable water exercises much influence 



hardness is quite sufficient, a water not too hard being generally pre- 

 ferred, though the total solids are likewise determined when a com- 

 plete analysis is made. 



Let us now briefly consider those inorganic constituents which are 

 generally regarded as important from a hygienic standpoint. 



