the Air and Water of Towns. 479 



sider it an accidental impurity, and collected some rain in 

 a porcelain vessel previously carefully cleaned. A smaller 

 amount was obtained, but still from 500 grains of the water a 

 sufficient quantity to make the smell distinct. I know that 

 organic matter has been found in rain-water, but I am not 

 aware that the smell of nitrogenized matter has been distinctly 

 observed. It has been obtained also by boiling down large 

 quantities : I have never found it to fail in evaporating as 

 little as 1000 grs. The amount was generally about '01 of a 

 grain in 1000 grs., but the average cannot be got without 

 trying many seasons and many places. 



1000 grs. collected on the 23rd of November, 1846, in a 

 platinum vessel, after raining thirty hours with little inter- 

 mission, gave with nitrate of silver a precipitate weighing 

 O'll grs. = 0"027 of chlorine, and with a salt of barytes 0-1, 

 equal to 0*0343 grs. of sulphuric acid, besides a perceptible 

 smell of organic matter as before. 



I do not adduce this analysis as of any great importance 

 in showing the amount ; the quantity operated upon is small, 

 and I was desirous, for the sake of the salts, not to expose it 

 to the contact of any vessel which could be acted on ; but I 

 mention it to show, that the quantity is not such as can be 

 only procured by the questionable process of boiling down 

 large quantities in vessels too large to admit of being perfectly 

 cleaned. 



The water is often alkaline — I say often, but I have always 

 found it so; by boiling this is lost, proving, as I think, that 

 there is more carbonate of ammonia set free from the burning 

 of coals than is necessary to saturate the sulphuric acid in 

 the atmosphere. 



The air is often acid, as evidenced by test-papers exposed 

 to it ; and it certainly proves very acid when certain quantities 

 of coal are burnt. 



It would have been well to have examined water from the 

 country falling at the same time, but being persuaded that 

 water so impure would long ago have been examined if it 

 even fell over large districts in such a state, I preferred look- 

 ing to its origin. 



As far as I am aware no examination of unventilated places 

 has given us a good proof that carbonic acid is the greatest 

 agent in making them so actively injurious. I breathed, and 

 had others to breathe, through a bent tube into a large jar, 

 and examined the moisture in the jar. As it always con- 

 tained organic matter in large quantities, I inferred that the 

 same must occur when the [jcrspiration and breath con- 

 dense upon the windows of crowded rooms. 



