64 DR. R. ANGUS SMITH ON THE EXAMINATION 



^^ In the oxygen column 6 and 3 may be left out. 



" The first and under might be called the first quality of 

 water; from 0*1 to 0*2^ the second; 1 would be the 10th. 



" It is considered better to acidify the water before add- 

 ing the permanganate ; this is done by adding three drops 

 or water- grain measures of sulphuric acid to 1000 grains; 

 ■^some water will demand more; the object is to attain 

 acidity equal to about three drops of sulphuric acid in 

 1000 grains of distilled water. I find Dr. Miller says 50 

 grains of diluted sulphuric acid (1 of acid to 3 of water) 

 added to 8 ounces of water. Acid enables the oxygen to 

 act on more matter and more rapidly ; and the calculations 

 are made on the supposition that acid is used ; the pro- 

 portions from difi*erent waters are not much changed by 

 acid. Alkalies prevent the action, although they may 

 prepare some of the matter to be more readily oxidized : 

 when the colour has been difficult to see, the chameleon 

 has been used with alkali instead of acid, in which case a 

 green colour is obtained, which is more easily recognized 

 in many cases, and serves as a corroboration.^^ 



As an illustration of the mode of examining water so as 

 to obtain the first and the second conditions, if we may 

 so call them, of organic matter, I will quote here a short 

 paper, read at the Philosophical Society of Glasgow, on the 

 water of the river Clyde. I think I there found the proper 

 use of the permanganate of potash. I found at last a very 

 sharp separation between those substances that decompose 

 the permanganate at once and without acid, and those 

 which do so on the addition of acid and after a short time. 

 So decided is this that I consider them as indicating two 

 diff'erent conditions of organic matter. 



^^ I lately adopted a mode of examining water by which 

 is seen, as I believe, the amount of organic matter readily 

 decomposed, and the amount actually decomposed, or the 

 amount of putrid gases resulting from decomposition and 



