38 DR. R. ANGUS SMITH ON THE EXAMINATION 



own which would guide me to consider it a sufficient test 

 for the total quantity of organic matter. 



Bodies of the third class I was therefore inclined to 

 estimate quantitatively by drying and weighing, after- 

 wards ascertaining the condition of the matter as of most 

 importance. 



Organic matter of the fourth class was estimated by the 

 amount of nitrites in the water^ because their existence 

 showed that the matter was oxidizing but had not had 

 time to complete the action. 



Bodies of the fifth class were estimated from the nitrates, 

 as in that case the action was finished. 



Bodies of the sixth class were reckoned from the absence 

 of bodies of the seventh class, which latter class, again, 

 were considered to exist when they were accompanied 

 by an unusual amount of chlorides, supposing care to 

 be taken to discover that other sources of chlorides did 

 not exist. 



It is not to be expected that any of these divisions 

 should be sharply defined; but the one most difficult to 

 decide upon, to all appearance, is really that which I have 

 found, with proper precautions, scarcely ever to fail me, 

 though it has been used in hundreds of instances, and for 

 many years — namely, the test for animal matter. 



Mr. Wood had written previously to the publication 

 alluded to, and about the same time Prof. W. A. Miller ; 

 but I am not aware that any one endeavoured to distinguish 

 the various conditions of the organic matter. I am, and 

 was^ desirous of showing that organic matter is not neces- 

 sarily hurtful j we speak of it in water as an evil, to be 

 measured by the balance, whilst there is as much difference 

 in the qualities of that found in water as there is between 

 good wholesome meat and putrid flesh. 



I was desirous also of showing the true value of the per- 

 manganate^ which is capable of acting on one, but scarcely 



