PROCEEDINGS OF THE PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
135 
Hydrogen could also be prepared by passing steam— 
that was gaseous water—over red hot iron, which united 
with the oxygen and set free the hydrogen. This the 
lecturer showed by means of a “Fletcher’s furnace,” and 
explained that by a similar apparatus oxygen could be got 
from water by passing chlorine along with it through a hot 
tube, when the chlorine united with the hydrogen and 
set free the oxygen. Speaking of the properties of 
hydrogen, the lecturer illustrated its lightness by 
causing a balloon, filled with it, to rise in the air. 
The inflammability of hydrogen was shown by means of a 
jet of that gas; and musical sounds were produced by 
holding tubes of various lengths over the jet—the sound 
being produced by the explosions which took place in the 
the tubes. Although hydrogen was a non-supporter of 
combustion, the lecturer, by various experiments, proved 
that the terms combustible and non-supporter of combus¬ 
tion were only relative, as oxygen, or ordinary air, could 
be made to burn in hydrogen. He next spoke of the pro¬ 
perties of oxygen, and, by experiments, showed that steel 
wire, which did not burn at all in air, burned very bril¬ 
liantly in oxygen. Mr Walker next referred to the im¬ 
purities in water, which, he said were of three kinds— 
gaseous, suspended solid matter, and dissolved solid 
matter. Rain water was the purest kind of water which 
was found upon the earth ; but even rain water was not 
perfectly pure, for, as it fell, it dissolved the gases in the 
air—oxygen, hydrogen,carbonicacid,and minute quantities 
of ammonia. Since, however, hot water dissolved less gas 
than cold, by heating the water it would give off a quantity 
of gas. The insipidity of boiled water was caused by the 
want of dissolved gas. Ammonia, if present, could not be 
got rid of by boiling, but they possessed a very delicate 
test for it in a substance called “ Nessler’s Re-agent,” by 
which as small a quantity as one-two-hundredth of a grain 
of ammonia could be detected in half-a-pint of water. 
Water, as it passed over the surface and percolated through 
the soil, not only carried with it sand and soil, but also 
dissolved the soluble substances of the soil and rocks. 
What was dissolved depended entirely upon the kind of 
rock and soil over which the water flowed. Suspended 
solid matter, he said, might easily be removed by filtra¬ 
tion through sand, charcoal, or porous paper. It was 
evident, however, that dissolved matter could not thus 
be separated. In that case they must distil the water 
_that was, turn it into steam, and then cool the steam, 
when the solid matter would remain behind. By means 
of certain “re-agents” the chemist could discover im¬ 
purities which could scarcely be detected by the ordinary 
observer. Hard water, he said, was one which did not 
at once form a lather with soap. If a little soap solution 
were poured into water which had a small quantity of 
gypsum or sulphate of lime dissolved in it, a curdy sub¬ 
stance was formed in the water, and a lather was not pro¬ 
duced until more soap solution was added. The hardness 
produced by gypsum, and similar substances, was called 
permanent, because it could not be removed by boiling the 
water. If carbonic acid were breathed from the lungs 
through lime-water, the water was turned milky from the 
production of chalk or carbonate of lime, but if more car¬ 
bonic acid were passed through, the water would then be¬ 
come clear again. The reason was that water, charged with 
carbonic acid, would dissolve chalk. If such water were 
heated, the carbonic acid would be expelled from the 
water, and the result would be that the milkiness would 
be reproduced. In the same way water, charged with 
carbonic acid from the air, or from decaying vegetable 
matter, if it passed over a chalky region, dissolved the 
chalk, which was deposited again when the carbonic acid 
was removed, either when the water simply reached the 
open air (as in the production of stalactites and stalag¬ 
mites) or when it was boiled. It was that which caused 
the furring of kettles and boilers. In Perth the water was 
very soft, and these effects were not much noticed, but in 
some places the furring had to be removed periodically by 
the hammer. Mr Walker then glanced briefly at the sub" 
ject of crystallization, in which water played an important 
part. Substances which crystallized, very often contained 
water, as, for example, ordinary washing soda which, when 
it was exposed to the air, lost its water, and became a white 
powder. Different substances crystallized in different 
forms. Hot water generally dissolved more salt than 
cold water did, and if a salt were dissolved in hot water, 
it generally crystallized out when the water cooled. Some 
substances, however, did not crystallize out if they were 
kept undisturbed. Mr Walker illustrated this by show¬ 
ing a solution of alum dissolved in boiling water in a flask, 
which was plugged with cotton wool. The alum did not 
crystallize out on cooling if the air had not free access to 
it, but whenever the plug of cotton wool was removed it 
immediately crystallized to a solid mass. 
LECTURE ON COLOURING MATTERS. 
At 9.15 a large and appreciative audience assembled in 
the Society’s Lecture-Room, when 
Mr Rufus D. Pullar, F.C.S., gave an interesting ad. 
dress (illustrated with numerous experiments) on colour¬ 
ing matters, with special reference to aniline dyes. All 
colouring matters, he said, might be divided into two 
great classes—1st, the natural colouring matters, or those 
