[Footnote: Abstract of paper read before Section C (Chemical Science),
British Association meeting, York.]
By PROFESSOR W. CHANDLER ROBERTS, F.R.S., and T. WRIGHTSON.
The authors described their experiments on the fluid density of metals
made in continuation of those submitted to Section B at the Swansea
meeting of the Association. Some time since one of the authors gave an
account of the results of experiments made to determine the density of
metallic silver, and of certain alloys of silver and copper when in a
molten state. The method adopted was that devised by Mr. R. Mallet, and
the details were as follows: A conical vessel of best thin Lowmoor plate
(1 millimeter thick), about 16 centimeters in height, and having an
internal volume of about 540 cubic centimeters, was weighed, first
empty, and subsequently when filled with distilled water at a known
temperature. The necessary data were thus afforded for accurately
determining its capacity at the temperature of the air. Molten silver
was then poured into it, the temperature at the time of pouring being
ascertained by the calorimetric method. The precautions, as regards
filling, pointed out by Mr. Mallet, were adopted; and as soon as the
metal was quite cold, the cone with its contents was again weighed.
Experiments were also made on the density of fluid bismuth; and two
distinctive determinations gave the following results:
10.005 )
) mean 10.039.
10.072 )
The invention of the oncosimeter, which was described by one of the
authors in the "Journal of the Iron and Steel Institute" (No. II.,
1879, p. 418), appeared to afford an opportunity for resuming the
investigation on a new basis, more especially as the delicacy of the
instrument had already been proved by experiments on a considerable
scale for determining the density of fluid cast iron. The following is
the principle on which this instrument acts:
If a spherical ball of any metal be plunged below the surface of a
molten bath of the same or another metal, the cold ball will displace
its own volume of molten metal. If the densities of the cold and molten
metal be the same, there will be equilibrium, and no floating or sinking
effect will be exhibited. If the density of the cold be greater than
that of the molten metal, there will be a sinking effect, and if less a
floating effect when first immersed. As the temperature of the submerged
ball rises, the volume of the displaced liquid will increase or decrease
according as the ball expands or contracts. In order to register these
changes the ball is hung on a spiral spring, and the slightest change in
buoyancy causes an elongation or contraction of this spring which can
be read off on a scale of ounces, and is recorded by a pencil on a
revolving drum. A diagram is thus traced out, the ordinates of which
represent increments of volume, or, in other words, of weight of fluid
displaced--the zero line, or line corresponding to a ball in a liquid of
equal density, being previously traced out by revolving the drum without
attaching the ball of metal itself to the spring, but with all other
auxiliary attachments. By means of a simple adjustment the ball is kept
constantly depressed to the same extent below the surface of the liquid;
and the ordinate of this pencil line, measuring from the line of
equilibrium, thus gives an exact measure of the floating or sinking
effect at every stage of temperature, from the cold solid to the state
when the ball begins to melt.
If the weight and specific gravity of the ball be taken when cold,
there are obtained, with the ordinate on the diagram at the moment of
immersion, sufficient data for determining the density of the fluid
metal; for