FACTS AND OBSERVATIONS. 
615 
Schlossberger to be so delicate a test for the presence of 
sulphur, that its existence in a single hair may be recognised 
by it. The solution is changed blue if only a trace of sulphur 
be present. 
Estimation of Nitric Acid. —M. Reich has found that 
powdered quartz drives off the nitric acid from nitrates, and 
particularly the alkaline nitrates, at a barely perceptible red 
heat. This reaction, he says, may be available in the deter¬ 
mination of nitric acid by difference. The nitrate is merely 
heated with four or six times its Aveight of quartz in fine 
powder. The presence of chlorides and sulphates does not 
affect the process, the nitrates alone becoming decomposed. 
Use of Watery Vapour in the Air. —Besides the 
well-known value of moisture in the atmosphere for the sus¬ 
tenance of the life of vegetables and of man, through the 
processes of evaporation and condensation, which are ex¬ 
ternally going on, and the mutual dependence of the one on 
the other. Professor Tyndall has demonstrated that the vapour 
of the atmosphere has the power of absorbing heat—and if 
of absorbing, of giving it out again—ninety times greater 
than the air which carries it, if so be this latter have its 
power of absorbing radiant heat reduced to unity. Were 
our atmosphere perfectly dry, the extremes of temperature 
would be excessive. The sun w^ould burn us during his 
appearance above our horizon, and when his influence was 
withdrawn the loss of warmth would be violent and rapid. 
The removal of the aqueous vapour from the atmosphere of 
England for a single night, we are told by him, would be 
attended by the destruction of every plant which a freezing 
mixture could kill. Watery vapour, as a great absorber of 
caloric, enables our atmosphere to grow warm, and thus we 
live in an agreeably diffused heat; while on mountain tops, 
W'here the air is very dry and the solar rays strike with com¬ 
paratively undiminished force, severe extremes of heat and 
cold are experienced. To our moist skies, also, says the pro¬ 
fessor, we owe the beautiful complexions of our women, 
which we should be sorry to exchange for the various grada¬ 
tions of orange, tawny, brown, and black, which so-called 
better climates produce. Nor must vapour be supposed to 
have any necessary association with turbid skies. It is when 
undergoing precipitation that it disturbs the deep, clear blue. 
When in solution it improves the colour of the atmosphere, 
and leaves distinct the vision of terrestrial objects and of the 
moon and stars. 
