722 
CHAPTERS FOR STUDENTS. 
compared with others of the established methods, show favourably for the 
former. The bark is to be finely powdered, and mixed with quicklime. 100 
grains of bark to 250 of lime form a convenient quantity to operate upon ; 
ithe mixture is damped with water, and then dried. The dry mass is then 
thoroughly exhausted with boiling 90 per cent, alcohol, and the solution fil¬ 
tered. To the filtered liquid a little dilute sulphuric acid is added, and the 
precipitated sulphate of lime filtered off; the greater part of the spirit may 
be distilled or evaporated away, and then evaporated nearly to dryness by the 
aid of a water-bath. A little water is added, the liquid filtered, and caustic 
soda added. The white precipitate of the alkaloids thus obtained, is collected 
in a weighed filter, dried thoroughly, and then Aveighed. 
To separate the bases from each other, the precipitate is digested in a flask 
with ether, the ethereal solution decanted, and the residue washed with ether. 
The ethereal-solution, united with the washings, is evaporated to dryness,^ 
and dissolved in a dilute sulphuric acid of known strength ; the solution, if 
necessary, is filtered and precipitated with a titrated solution of soda, in 
quantity sufficient to neutralize the sulphuric acid added. The residual 
alkaloid, insoluble in the ether, is treated in the same manner. The bases 
procured are in a state of considerable purity. 
CHAPTERS TOR STUDENTS. 
BY WILLIAM A. TILDEN, B.SC. LOND., 
DEMONSTRATOR OF PRACTICAL CHEMISTRY TO THE PHARMACEUTICAL SOCIETY. 
HEAT ( continued ). 
13. For the measurement of temperatures within moderate limits (from 
about — 30° to 600° F.), the mercurial thermometer is by far the best. Spirit 
of wine is employed to charge the thermometer when the temperatures to be 
observed are very low, alcohol never solidifying at any temperature hitherto 
producible. The expansion of air or other gas is made the measure of very 
high temperatures. But mercury presents peculiar advantages, one of which 
is that it does not adhere to the tube; another, that it gives its indications 
quickly. This is chiefly dependent upon the fact, that it has a low “ specific 
heat.” 
14. To understand the meaning of this phrase, such experiments as the 
following must be carefully thought over. 
a. If equal weights of water and mercury are successively placed over the 
same lamp, and the time occupied by each in passing from the temperature 
of the air (say 50° F.) to some higher point (say 150° F.) noted, it will be 
found that the mercury acquires that temperature in about ~ of the time 
occupied by the water. 
b. If the mercury and water are now allowed to cool down again to the 
starting-point, being both deposited in some place where they may be subjected 
to exactly the same external influences, the mercury will cool doAvn again in 
about -/q of the time occupied by the water. 
c. If water at 150°, and mercury at 50°,—equal weights,—be shaken up 
together till the temperature of the two is the same, it will be found that 
they both indicate by the thermometer between 146° and 147° ; the water 
will have lost about 32°, and the mercury will have gained about 96°, or 30 
times 3*2. 
If water had been substituted for mercury in the last experiment, the 
temperature of the mixture would, of course, have been halfway between the 
two, or 100°. 
