FOR MEASURING THE EXPANSION OF SOLIDS. 
267 
a diminished scale, at fig. 3. a is an iron tube about two inches diameter, and 
closed at the bottom : b is a black-lead tube closed at the top, and fitted to 
the mouth of the former by grinding : c is a smaller black-lead tube projecting 
from the side of the latter near its upper end, and likewise fitted to its place 
by grinding. The whole forms a kind of alembic, which may be readily put 
together, and in which mercury may be easily boiled on a common fire, and 
the vapours collected without loss or annoyance to the operator. The register 
was fixed in its place by a wire, so that when mercury was poured into the 
iron bottle it was prevented from floating. The mercury in this experiment 
rose a little above half the length of the register. The whole apparatus was 
then placed upon a fire, and in ten minutes the mercury began to boil : in 
ten minutes more it freely distilled over ; and in ten minutes further the 
apparatus was removed, the register taken out and allowed to cool. The arc- 
measured upon the scale was in this instance 1° 17'- 
The experiment was repeated, merely having the head of the alembic off, 
and suffering the mercury to boil freely in the iron bottle for a quarter of an 
hour. The arc measured was 1° 23'. 
The register was next allowed to float upon the mercury, so that when the 
head of the alembic was adjusted and the mercury made to boil, it was not 
immersed in the metal, but surrounded by its vapour: the reading was 1° 16'. 
A repetition of this arrangement gave 1° 23'. 
In another repetition of the experiment, the time was extended to twenty 
minutes from the first boiling of the mercury ; the reading of the scale was 
1 ° 20 '. 
Again ; the time was reduced to ten minutes, and the measurement was 
1° 23'. 
In the various repetitions of this experiment the mercury freely distilled 
over, and the temperature was such, that every part of the black-lead tubes, in 
which the vapour circulated, would just scorch, but not blacken, a piece of 
writing paper held against them. 
