30 REPORT—1848. 
the salts which are not precipitated by boiling, tasted even when cooled ex- 
cessively vapid. 
Soda-water with alkaline salts, when boiled, is excessively disagreeable. 
Twenty grains of common salt cause a gallon of water to taste vapid, and two 
grains and a half of saltpetre or nitrate of potash have a still stronger effect. 
The nitrate of lime in the water of towns mixed with the common salt 
gives an extremely nauseous taste to water, and causes it also to taste some- 
what soft, although possessing such a large amount of matter as I have 
mentioned. Acids control this taste; carbonic acid, we have seen, prevents 
vapidness. A few drops of any acid render water pleasanter in a warm day. 
Acidity is strongly allied to coolness of the taste, as general experience 
shows. Acid drops and oranges in hot rooms are used for this reason, and 
vinegar also by travellers in hot climates. A few drops of any acid, vitriol, 
for example, are used by the workmen in chemical works to improve the 
water in warm weather. 
Alkalies cause water to appear soft. Beer which is called hard is acid, 
and becomes soft by adding soda; this is common. 
The salts of lime seem to be the only salts which do not easily render 
water disagreeable. 
I may conclude this paper with a short summary of what I have said about 
water and air. 
Summary.—1. That the pollution of air in crowded rooms is really owing 
to organic matter, not merely carbonic acid. ; 
2. That this may be collected from the lungs or breath, and from crowded 
rooms indifferently. 
8. That it is capable of decomposition, and becomes attached to bodies 
in an apartment, where it probably decomposes, especially when moisture 
assists it. 
4, That this matter has a strong animal smell, first of perspiration, and 
when burnt, of compounds of protein, and that its power of supporting the 
life of animalcules, proves it to contain the usual elements of organized life. 
5. Organic matter of dew contains less nitrogen. 
6. The slightly alkaline state into which soil is put at certain periods of © 
the year, give it a facility for emitting vapours; whilst all vapours of water 
from organic matter contain organic matter. 
7. Water purifies itself from organic matter in various ways: by forming 
nitrates, as in sewers, and in the neighbourhood of cesspools and church- 
yards, under streets, in manured grounds, and other repositories of organi¢ 
animal matter. 
8. This may be done in a laboratory on a small scale, where animal mate 
ter, by means of a sand-filter, may be converted into nitric acid. 
9. In the larger operations of nature the carbon also is oxidized. 
10. Sulphuretted hydrogen is also oxidized on a small scale by a filter, | 
being converted into sulphuric acid. 
11. A filter therefore, as an oxidizing agent, acts in proportion to its 
cubic contents. 
1%. Water falling on the surface of the ground gets rapidly saturated with — 
organic matter; but in passing through the soil gets filtered and the matter 
oxidized, making the porous soil and the air the great agents of purification 
in a country; whilst drainage will act by removing organic impurity as well 
as mere water. 
13. All wells near houses and all wells in towns contain nitrates, which 
may be easily traced to sewers or accumulations and outlets of refuse. 
