HALOID COMPOUNDS OF SILVER, MERCURY, LEAD, AND COPPER. 1155 
The following volumes correspond to the temperatures given :— 
Volume at 
99 
99 
99 
99 
99 
99 
99 
3J 
0° C 
100 
200 
223 
256 
284 
309 
319 
400 
500 
melting point (514° C.) solid 
„ „ (514 C.) liquid 
= 1-000000 
=1-004998 
=1-009996 
= 1-011145 
= 1-011804 
= 1-011804 
=1-010805 
=1-010805 
=1-024303 
=1-040968 
= 1-043301 
=1-103307 
The fact that the alloy does not commence to expand again after its phase of con¬ 
traction till a temperature of 324° C. has been attained, necessitated the raising of the 
temperature to an unusual height. The ceresine employed for heating, ignites when 
air has free access to it at 300° C. Moreover, ordinary thermometers which contain a 
vacuum above the mercury cannot be heated above 330° C. as the mercury then com¬ 
mences to boil. But these difficulties were overcome, and the ceresine was even carried 
to a temperature of 340° C. by closely covering the experimental trough with a brass 
plate so as to shut out direct access of air, leaving room only for the thermometer and 
for the working of the levers. Great care was taken to screen the rest of the appa¬ 
ratus by bright metal plates from the effects of radiation. The thermometer difficulty 
was got over by leaving a little air in the tube above the mercury, by which means it 
could be heated to 350° C. with readiness, but, of course, it must be borne in mind that 
the readings at these high temperatures are less reliable than those at lower ranges. 
It was not found to be practicable to work above 340° C., as at such a temperature 
the ceresine is liable at any moment to ignite; moreover it fumes furiously, and begins 
to decompose. The dense acrid vapours are particularly irritating to the lungs and 
eyes. Nevertheless for temperatures up to 340° C., ceresine or a paraffine of high boil¬ 
ing point, is, I believe, the most convenient medium that we possess. 
2. Copper-silver iodide alloy, Cu 3 T 2 .2AgI. 
The percentage of iodide of silver was now augmented to 55 by the addition of 
another molecule.. 
Cu 2 I 2 .2AgI contains;— 
Iodide of copper . . = 44-6934 Copper.= 14‘8624 
Iodide of silver... = 55-3066 Silver.= 25'3939 
Iodine ..... = 59-7437 
1000000 100-0000 
