92 



A. Pedler — On the past and present 



[Xo. 2, 



Professor "VVanklyn says with regard to this method of analysis, that 

 by the aid of the ammonia process, we are now able to divide potable waters 

 into three broad classes : 



(1) Waters which are of " extraordinary organic purity," ^■. e., those 

 which are almost free from any nitrogenous organic matter, and which con- 

 tain less than 05 23arts of albuminoid (or total) ammonia per million of 

 water. 



(2) " Safe waters," which are devoid of any excess of nitrogenous 

 organic imjmrity, and which contain from 0'05 to O'lO parts per million 

 of albuminoid ammonia. 



(3) Waters which are " dirty," i. e. charged with an abnormal quantity 

 of .organic matter, and which contain more than O'lO parts of albuminoid 

 ammonia per million of water. 



The second important consideration is the determination of the 

 amount of chlorine present in the water. Chlorine occurs in potable water 

 in combination with several metals (as chlorides), such as sodium, magnesium, 

 calcium and possibly potassium. The amount of chlorides or of chlorine 

 present in drinking water is in itself of little importance, for as most people 

 are aware, com.mon table salt is simply sodium chloride, and this substance 

 is a necessary ingredient of our food. The water analyst determines the 

 amount of chlorine present in water because the presence of this substance 

 m water is in most instances a clear indication of contamination by sewage 

 in some form or another. 



It will be understood how this is the case when we consider that rain 

 water, which is the source of all water supplies when collected in the open 

 country and at inland stations is practically free from chlorine. Drink- 

 ing water also which is uncontaminated by sewage is comparatively free from 

 this substance, but sewage and urine,* are highly charged with chlorides, of 

 which common salt is probably in largest quantity. If then a given sample of 

 water contains no chlorine or very little, it cannot have been in contact with 

 sewage, but if any considerable amount is present in a water, which is 

 known not to have come from a tidal river or from any geological for- 

 mation where deposits of salt are found, such a water would be viewed 

 with the gravest suspicion, and if this were supported by other 

 evidence, the water would at once be condemned. Unpolluted river and 

 sjoring waters usually contain less than ten parts of chlorine per million 

 of water, average town sewage in England about one hundred and ten 

 parts ; shallow well water may contain any quantity from a mere trace 

 up to 500 parts or even more. The amount of chlorides is scarcely 

 affected by any degree of filtration through soil ; thus the effluent water 

 from land irrigated with sewage contains the same proportion of chlorine 

 * Human lu-ine contains about 5000 parts of chlorine per million of liquid. 



