41 
in appearance and character from those collected in Bristol, that the discrepancy 
has been thought worthy the notice of the Naturalists' Society. 
The salts dissolved in rain-water falling in manufacturing towns are very 
considerable in amount, and become of great importance in the calculations of 
analytical chemistry. The moisture on the earth rises by evaporation into 
the atmosphere at an average of .033 inch every 24 hours. This would 
amount to 120 cubic feet, or 720 gallons from every acre. The vapour retain- 
ing its vesicular form floats in the atmosphere, forming what we call clouds. 
When the atmosphere becomes too light, or cold, or from the presence 
of electricity, the vesicles coalesce, and becoming too heavy for suspension 
fall to the earth as rain. 
At this stage rain-water is very pure, probably the purest kind of natural 
water, only containing traces of Ammonia. Rain, falling in the open 
country, leaves scarcely any residue when evaporated to dryness ; but 
when falling into the midst of a crowded city, the atmosphere of which is 
filled with all inorganic and organic abominations, the result is far otherwise. 
The drops of rain freely dissolve these impurities, and when collected will 
yield them up to the examiner. The greater the purity of the water, the 
greater its solvent powers are known to be. 
The smoke from our factories— bone black, soap, and candle works— the 
combustion of coal from hundreds of chimnies, the effluvia from dwellings, 
the odours we admire and the smells we dislike, all combine to pollute the 
air we breathe. Consequently these impurities are dissolved and brought 
down by every shower of rain in very large quantities. 
The specimens alluded to this evening were both collected on September 
6th; one in North Street, and the other in King Square. The rain was 
what we call "drizzling" and was collected by means of a clean wide glass 
funnel inserted into the mouth of a bottle and afterwards evaporated in a 
warm air apparatus at a very gentle heat. The amount of residue was 
startling, and the difference between the two samples very surprising, 
although the two localities were so short a distance apart. That in North 
Street was very acid to test paper, while that in King Square was decidedly 
alkaline from the presence of Carbonate of Ammonia, and effervesced when 
touched with an acid. 
The following were the analyses calculated in grains per gallon:— 
