452 
POPiJLAK SCIENCE PEYIEW. 
linson contends tliat siipersaturation exists in fact, as well as in appearance, 
and that there is no proof of any molecular change in such solutions, such 
as to lead to the formation of a more soluble salt. 
The Magnetic Polarity of Magnetic Oxide of Iron. — M. Sidot has already 
shown that iron-pyrites may he given magnetic polarity by passing a 
current of hydrosulphuric acid over the magnetic oxide. He now states 
that the direction of the polar axis appears to be in relation to the 
position of matters at the moment of their formation with reference to the 
magnetic axis of the globe. M. Sidot has tested his supposition further 
by examining the behaviour of the oxide of iron, FejO^, examining whether 
it suffered the same physical modifications, being placed in the same con- 
ditions, as magnetic pyrites, and whether the polarity was produced by the 
earth by removing all causes foreign to terrestrial action. When a tube of 
refractory clay is placed parallel to the magnetic needle, in a furnace free 
from iron, and in the tube a platinum boat filled with colcothar, which is 
heated to bright redness in a current of air for an hour, the result, after 
cooling, is a strongly agglomerated grey oxide possessed of magnetic 
polarity. The extremity of the oxide turned towards the north is a south 
pole ; it energetically repulses the pole of a magnetic needle pointing to the 
north of the earth. Magnetic oxide is likewise obtained by calcining col- 
cothar in a platinum crucible. The upper extremity of the mass presents 
a pole opposed to the south pole of the globe, and the lower extremity an 
opposite pole. To obtain masses possessed of greater magnetic polarity a 
different disposition was made. A piece of iron plate, in the form of a tube, 
was suspended in a clay tube, placed vertically in a furnace traversed by a 
very rapid current of air, and heated to bright redness for the time neces- 
sary for the complete oxidation of the iron. Tubes of oxide were thus 
obtained possessed of magnetic polarity, and strongly repulsing the poles of 
the magnetic needle. The polarity is always dependent upon the position 
of the iron plate. The magnet produced in this way was replaced in the 
furnace, reversed, and heated in the same conditions of temperature as 
before for one hour ; after cooling, the poles were found to be reversed ; that 
pole which is formed at the upper extremity is always similar to the north 
pole of the earth. — Foreign Correspondence, Chemical News. 
A simple and useful Form of Aspirator is thus described by Professor 
Leeds, in a recent number of the American Journal of Science ; — A pail con- 
taining water is placed at the edge of the table, and to a stop-cock which 
is attached to the side of the pail near the bottom a tube of two or three feet 
in length is connected, to carry off* the water to a bucket placed on the 
floor below. When the bucket is filled, the stop-cock is turned off for a 
moment, and the water poured back into the pail. To the top of the stop- 
cock tube, which should be made straight and somewhat longer than usual, 
and in front of the stop-cock itself, a short vertical tube is attached, and 
connected by means of india-rubber tubing with the wash-bottle or other 
vessel through which gas is to be drawn. On partially opening the stop- 
cock, the deficiency of water is made up by a large quantity of air or gas, 
which is drawn in through the vertical tube above mentioned. 
Scientific Photometry. — The old sperm candle is known to all who have 
used it to be a most unreliable standard for photometric observation. Mr. W. 
