DR. T. S. HUMPIDGE ON THE ATOMIC WEIGHT OF GLUCINUM. 
G09 
each side. The wires from those solenoids terminate in four points of German silver 
at the end of the hoard (only one of which, J, is shown in the figure), which when the 
calorimeter is drawn up into its place under the heater come into contact with four 
springs of the same metal (K) connected with the battery and a switch. The board 
on which the calorimeter and its appurtenances are fixed can be moved by strings from 
the position shown in the figure to that exactly under the heater and back again.* 
To obtain accurate readings of the different temperatures, two standard thermo¬ 
meters were first constructed, with a millimeter scale, and calibrated by Gay-Lussac’s 
method, using Mr. F. D. Brown’s excellent little instrument.t These two read 
between about 5° and 105° C., and 1 millim. is about equivalent to 0 o, 2 C. They 
were compared with one another for every half degree between 8° and 20° C., in a 
large bucket of water, kept suitably agitated, and in only one instance differed by 
more than 0 o, 02 from one another. The bent thermometer (T 2 ) was more open, 
and 1 millim. was about equal to 0°T C. It was very carefully compared, by two 
series of experiments, with the two standard thermometers together, and the mean 
temperature taken when they differed from one another. The thermometer T l5 used 
for the heater, read accurately to 0 O- 05 C., was corrected for the boiling point, but not 
calibrated; the correction for the exposed thread was determined experimentally, and 
was found to be 0 o, 03 less than given by the usual formula : — 
C —m (T — t) n. 
The water-equivalent of the thermometer T 3 was calculated, from the weight of 
mercury which it contained, and the weight of glass immersed, to be 0'5 gramme, 
which agreed with experimental results. 
Readings of the temperature to which the substance was heated are thus correct 
to at least 0°T C., and of the calorimeter to 0 o, 01 C. 
The liquid used in the calorimeter is French turpentine, purified and redistilled. 
Taking the specific heat of this liquid as 0'4, and its specific gravity as 0'87, about 
i 28 small calories are requisite to raise the temperature of 80cc. through one degree, 
and only a small weight of the substance is required. Thus, for silver, the quantity 
necessary would be WxV-uh — 6 grammes (circa), and for aluminium iofbs—1 gramme 
(circa) for a fall in temperature of 80° : much smaller weights than are required for 
any other accurate method, except Bunsen’s. With a temperature difference of 
l o, 00, and reading to 0 o, 01, the mean error cannot well be smaller than 1 per cent., 
and with the instrument in its present form, this is, in fact, the limit of error. 
More accurate results might be possible with a still smaller calorimeter, and a still 
more open thermometer. 
One possible objection to the use of turpentine was loss by evaporation during the 
* A battery-power of four quart Bunsen or Groves’ cells is necessary. More convenient than this 
is a bichromate battery so arranged that the zincs can be lowered into the liquid when required, 
t Phil. Mag. [5], xiv., 57. 
