, 
Ladberaiory Ocewrrences. 46% 
thought prudent to repeat the experiment again, as the third 
iube contained a much larger quantity of the preparation. 
This pyrophorus had been observed to be unusually good, 
and when breathed upon in the air, kindled in many places 
at the same time, witha slight explosion. ‘The tubes, stop- 
ped with particular care, had stood within eight or ten feet of 
the fire, in the laboratory, and could not possibly have im- 
bibed moisture. The explosions doubtless resulted from the 
friction and pressure of the ramrod ; and they show us the 
necessity of care in regard to a substance, against which the 
books, we believe, give us no caution. 
It may be proper to mention that the pyrophorus was, in 
this case, prepared from a recipe furnished to me by Dr. 
Hare ; it wasas follows. ‘Take lampblack three, calcined 
alum four, and pearlashes eight parts—mix them thoroughly, 
and heat them well in aniron tube toa bright cherry red for 
one hour. © 
This pyrophorus rarely fails. When well prepared and 
poured out upon a glass plate and especially when breathed 
upon, it kindles with a series of small explosions, a little like 
those produced by throwing potassium upon water. There 
is even some danger to the face and eyes from the number 
and rapid succession of these little explosions, and one is for- 
cibly impressed with the idea that they must be owing to pot- 
assium. Since the discovery of this brilliant substance, there 
has been little doubt, that it is developed in greater or 
smaller quantities, during the formation of pyrophorus. The 
above process seems peculiarly adapted to the production of 
anunusual quantity of potassium, since there 1s in the mix- 
ture a large quantity of the alkali, and also of carbon, which, 
it is now known, is admirably adapted to the decomposition 
of potash. Ifa burning coal happen to drop into a silver 
crucible containing ignited caustic potash, there is a rapid 
succession of explosions, and the liberated potassium and 
potassuretted hydrogen burn with a brilliant flame and the 
fumes of regenerated caustic alkali are extremely conspicu- 
ous. Indeedit has long been known that charcoal will, by 
intense ignition, evolve potassium from potash. Curadeau 
first called our attention to this fact, and more recently Pro- 
fessor Brunner has shown that this process, skilfully con- 
ducted, is even preferable to any other. 
[See Bib. Univ. Jan, 1823, quoted in this Jotrnal yol. 
VIL. p. 372.] 
