176 BOAED OF AGRICULTURE. [Pub. Doc, 



decide which. Take ammonia, as another example. Con- 

 sider how few substances there are in nature which do not 

 contain either ammonia or the elements which form it. Rain 

 water collected before it reaches the earth contains a dis- 

 tinct amount of it ; nearly all organic substances contain 

 either it or its elements, — nitrogen and hydrogen. Would 

 we, therefore, be justified in rejecting uncontaminated rain 

 water because it contains ammonia? Certainly not, for we 

 know its source and origin. What is it, then, which renders 

 us suspicious of ammonia in water? It is not its quantity, 

 for even in sewage it seldom reaches more than 1.6 parts in 

 10,000, and we know that therapeutically we can give it, 

 combined with a carbonate, in the quantity of drachms. It 

 is evident, therefore, that it is not ammonia which we fear, 

 but it is the undoubted indication which the presence of 

 ammonia affords us of organic contamination. We cannot 

 isolate faeces, urine or putrid organic substances in water in 

 the form in w T hich they entered, for they have become dis- 

 solved or suspended ; their elements have undergone change ; 

 the nitrogen has broken up or combined with hydrogen, and 

 thus formed ammonia. In ammonia, therefore, we have our 

 index of the amount of organic nitrogenous substances in 

 drinking water, and in speaking of ammonia we are actually 

 speaking of organic nitrogenous matter. 



We have named chlorine also as a substance to. be sought 

 for. Now, chlorine in the form of gas, or dissolved in 

 water, is certainly a powerful germicide, and consequently 

 it might be argued that in the very small proportion in 

 which it is found it would be beneficial rather than other- 

 wise. But the chemist shows us clearly that the chlorine 

 does not exist in drinking water in a free state, but in com- 

 bination with other elements which render it of less value 

 as a germicide, but, on the other hand, make it a most 

 valuable aid in detecting impurity ; for the chlorine found 

 there comes only from two sources, viz., chlorides of the 

 metals, potassium, calcium or sodium, or chlorides of the 

 same bases contained in organic substances. It is certain 

 that chlorine derived from the chloride of sodium of inor- 

 ganic substances is quite harmless, and it has been sug- 

 gested that thirty to forty grains per gallon might be added. 



