52 DR. R. ANGUS SMITH ON THE EXAMINATION 



of silica, leading me to tliink that, by our usual modes of 

 estimating that substance, we were apt to make the amount 

 too small. I believe this acid to be the origin of that 

 bitterness which I have so often observed on the hills ; and 

 even in the very brilliant water from the hills, the two 

 processes have been going on at the same time — the forma- 

 tion of carbonic acid and the formation of the liquid acid. 



Apparently there are times, perhaps flood-times, when 

 the water does not become oxidized so much as usual ; and 

 then we find the bitterness as a result in a greater degree. 

 Although I had observed this for many years, I had not 

 known that the effects might be hurtful to those who 

 drank the waters. I met this year, accidentally, at Oban, 

 Professor Frankland, who told me of some gentlemen 

 whom he had met, who were very much inconvenienced by 

 the use of such water, and who actually took supplies of 

 other water with them to Inverness, at which place they 

 had found the river to cause diarrhoea. I am not aware 

 that that disease is more frequent at Inverness than else- 

 where ; but the water, or at least the substance in it, to 

 which I allude, seems to be unwholesome to those who 

 have not been accustomed to use it. 



Taking this view of the case, water collected in the 

 mountains is very different from that which has run down 

 into the plains. The age of the water also is a matter of 

 importance, and if kept long in deep reservoirs or in shal- 

 low reservoirs. 



If in shallow reservoirs, the water may be uniform 

 throughout ; if in deep reservoirs, the oxygen may never 

 be able to permeate to the bottom. At a depth of twenty 

 feet I have found more than twice as much organic matter 

 than was to be found on the surface. 



Water that comes down very rapidly may never be able, 

 in a practical period, to have the organic matter tho- 

 roughly oxidized. Water which purls down rather slowly. 



