560 
POPULAE SCIENCE EEVIEW. 
may be safely taken bave been given. The following ma}'' 
be regarded as an approximation to safe quantities. It may 
be said that a gallon of water should not contain of 
Carbonate of Lmie more than 
Sulphate of Lime „ 
Salts of Magnesia „ 
Chloride of Sodium „ 
Carbonate of Soda „ 
Sulphate of Soda „ 
These are the ordinary constituents of water_, but water 
from special circumstances may be rendered impure by very 
small quantities of other constituents. A water with very 
small quantities of iodide or bromide of sodium, the salts 
of h*on, lead, copper, arsenic, or antimony, might soon be- 
come very injurious to health. The presence of large quanti- 
ties of gases has also been objected to. Ordinary drinking water 
contains in the gallon about six cubic inches of nitrogen, of 
oxygen, and 5 to 7 of carbonic acid. These may be absent 
or in much larger extent without being injurious. There is 
one thing that should be recollected with regard to these 
gases, and that is, that they render the water sparkling to 
the eye and fresh to the taste, and that they are entirely got 
rid of by boiling. 
It is almost impossible for persons who have not had a chemical 
education, to analyse water with that degree of accuracy that 
would enable them to judge of any particular ingredient there 
is in water. Nevertheless, I think it quite possible for 
intelligent people so to test water as to come to a tolerably 
correct conclusion with regard to its purity. Most persons 
use their senses before drinking water. Thus its colour and 
transparency may be at once detected by the eye. So accus- 
tomed are we to the true colour of water, that we at once 
detect any departure from its natural appearance. Blue water, 
greenwater, yellow water, are immediately detected and regarded 
as unnatural. The transparency of water is also recognised 
as a natural and necessary property. Indeed, water should 
be at once rejected, unless its turbidity is known to depend upon 
some uninjurious agent. The taste of water is still more 
generally known. Any departure from the insipidity of water 
is usually detected. Such departure should be noted, and any 
strange tasting water should be rejected. The sense of taste 
is essentially connected with that of smell, and sometimes the 
exercise of taste and smell may tend to the '’detection of impu- 
rities in water. Even the sense of touch may be employed in 
the investigation of water, as the action of hard water, or 
20 grains. 
3 
3 
20 
20 
5 
jj 
V 
JJ 
