46 DR. R. ANGUS SMITH ON THE EXAMINATION 



capable of entering into active and unwholesome forms, 

 or had been ready to break up into instantaneous putre- 

 faction, or had been preserved, like a mummy, in carbolic 

 acid for a thousand years. 



From this observation regarding the ammonia, we are 

 clearly led to beware, in our schemes of irrigation by 

 sewage-water, that the land shall be overflowed before the 

 ammonia is thoroughly formed, or else, if the ammonia is 

 formed, that it shall not be subjected to loss by long ex- 

 posure to evaporation. 



We see, also, that nature provides here for the complete 

 obliteration of organic matter. It ceases altogether to be 

 found in the water. It may be traced, either as such or 

 as ammonia and carbonic acid, long after the bubbles of 

 carburetted hydrogen have ceased to appear, until at last 

 it dwindles down to an amount which is rather difficult to 

 remove from water, and which, so far as we know, may be 

 utterly disregarded. 



In the passage of organic matter we may observe, from 

 figures soon to be quoted, that the volatile and organic 

 matter diminished from 9*33 grains per gallon down to 

 5*04, even when there was an increase of fixed matter, and 

 that the decomposing matter in solution diminished still 

 more rapidly, in the ratio of 283 to 17. 



The organic matter having left the water, we may next 

 inquire whether any trace of its existence remains behind. 

 That trace we do find in the increased amount of alkalies, 

 sulphates, and chlorides. 



The alkalies and alkaline salts, but especially common 

 salt, are prominent. The whole of the common salt which 

 has been used as food, without the slightest loss, is found 

 in water, when vegetation has not removed it. The sulpliur 

 has become partly oxidized, leaving sulphates, whilst some 

 may have left in company with hydrogen. Phosphates 

 have been increased for a time ; but they rapidly fall, taking 



