THE YOUNG SCIENTIST. 
trates this fact, requires no special apparatus and is 
easily performed. Lay a block of ice across the back 
of two chairs, and over it pass a piece of fine iron 
we the ends of which have been twisted together. 
From the wire suspend as great a weight as the wire 
and chairs will support, say 50 to 100 lbs. It is evi- 
dent that since the extent of ice surface on which a fine 
wire will press is small, the pressure jper square inch 
on the ice must be very great. The consequence is 
that just beneath the wire the ice is melted, and the 
wire drops down a little. As soon as the wire falls 
however, the water above it is relieved from pressure 
and immediately freezes. In a short time therefore, 
the wire passes completely through the ice, and 
allows the weight to fall, while the ice is not broken, 
nor is any mark visible where the wire has passed 
through. 
Smoke Rings. 
One of the most beautiful, though perhaps not one 
of the most brilliant experiments in chemistry, is the 
formation of smoke rings by phosphoretted hydrogen. 
In a still room, dimly lighted and with a small au- 
dience, the bright, but short-lived flashes of light and 
the self luminous rings of smoke, gradually widening 
as they ascend, and forming a series, nearly extend- 
ing to the ceiling, are beautiful beyond description. 
Unfortunately however, phosphorus is not a very 
safe article to handle, and unless in careful and skil- 
ful hands, the preparation of phosphoretted hydrogen 
is apt to give rise to ugly accidents. The following 
experiment is without danger, and is very interest- 
Smoke Rings. 
ing and beautiful : Take an ordinary can, such as is 
used for tomatoes, etc., and in the bottom punch a 
clean hole, about one-third of an inch in diameter ; 
over the open end stretch a sheet of paper. This is 
best done by wetting some rough manilla or drawing 
paper, stretching it over the mouth of the can, 
and tying it down as in the figure. When dry, it 
will be perfectly smooth and tight like a drum. 
Throw a little smouldering brown paper into the can 
and it will soon fill it with smoke. If after a few 
seconds the can be held in one hand, and tapped 
31 
with the other, very perfect rings will issue with a 
speed proportionate to the strength of the tap. 
These smoke rings deserve careful study, and we 
will return to them again. 
Varnish for Paintings. — " A good varnish 
can be made as follows : Mastic, six ounces ; 
pure turpentine, one half ounce ; camphor, two 
drachms ; spirits of turpentine, nineteen ounces; 
add first the camphor to the turpentine. The 
mixture is made in a water-bath, and vi^hen the 
solution is effected, add the mastic and the 
spirits of turpentine near the end of the opera- 
tion, then filter through a cotton cloth. The 
varnish should be laid on very carefully. 
Steel Rust. — According to the Chemiker Zeit- 
uiKj, articles of steel which have become rusty 
may be cleansed by brushing with a paste made 
up of thirty parts cyanide of potassium, thirty 
parts curd soap, sixty parts of precipitated 
chalk, and a sufficiency of water. Great care 
is required in preparing and using this poison- 
ous mixture. 
The Camphor Barometer. — This toy, for it is 
little else, has been extensively sold as a reliable 
weather indicator. It was carefully examined years 
ago, however, and its indications were not found to 
be of any value. The reason of this is that the cloud 
which constitutes the "indicator" is formed either 
by pressure or by heat. Moreover the ingredients 
are apt to change with time and exposure, and this 
forms another element of uncertainty. The recipe 
as generally given is as follows : Dissolve two parts 
of gum camphor, one part of saltpetre, and one of 
sal ammoniac in 100 parts of 9'5 per cent alcohol, and 
add enough distilled water to precipitate a small 
portion of the camphor. Place this in a large glass 
tube with the upper end drawn out, so as to leave 
an opening not larger than a pin hole, or the end 
0 the tube may be closed with a good sound 
cork. The instrument is to be fixed in the open 
air, out of direct sunlight. 
Jtensine and Bensol.— These two names are 
often confounded with each, other. The first is usually- 
applied to the product from petroleum, and the second 
to that from coal tar. They differ considerably in their 
properties, and as benzol is extensively used in micro- 
scopy, etc., disappointment has frequently been occa- 
sioned to those who have used benzine instead. 
Eager remarks that petroleum benzine, on dissolving 
iodine, assumes a raspberry red color, while coal -tar 
benzine becomes vidlet. Asphaltum is soluble in coal- 
tar benzine and insoluble in petroleum benzine. 
