1817.) | On the Decomposition of the Earths. 195 
But when oil is substituted as the fluid represented by A B, acci- 
dents of this kind are not likely to happen. 1 have purposely ex- 
ploded the gas in the chamber C upwards of 20 times ; to prove the 
instrument. ‘The o7/, in these trials, was never driven from its 
lace; neither did the combustion of the gas cause it to take fire. 
ncouraged by the security it offered, I have increased the diameter 
of the tube mn, until it now equals 2, of an inch; and the con- 
sequence of this is, that the body of the flame represented by 0p, 
is of magnitude sufficient to act upon 100 grains of platinum, 
which are instantly fused by its intense action; and by dropping 
minute pieces of the metal into the boiling and burning mass, its 
bulk may be increased. Having commenced therefore with stating, 
as a result of the intense heat of the ignited gas, that globules of 
melted platinum were obtained weighing five grains,* you will 
judge of the increased power of the blow-pipe which has enabled 
me to obtain masses of the same metal in fusion weighing from 
100 to 150 grains, and upwards.¢ The combustion of iron, under 
the same circumstances, affords so beautiful a phenomenon, that I 
can recollect no instance of any chemical experiment to be com- 
pared with it; and when the two metals, platinum and iron, are 
fused together in a charcoal crucible, before the ignited gas, their 
joint combustion affords a pleasing and brilliant fire-work. 
But in describing the apparatus as being perfectly secure, there 
are, of course, certain Cautions to be observed. In using tubes 
with such large diameters as | have now mentioned, partial explo- 
sions of the gas within the safety cylinder, C, will more fre- 
quently happen, and the detonations will be more powerful; 
therefore, in these cases, it is always necessary to examine the 
eylinder for the purpose of seeing that the oil has not been forced 
into the reservoir; but remains at its proper level, A, B. If this 
be neglected, the operator will be liable to the consequences 
* See Journal of the Royal Institution, iii, 107. 
+ It was desirable that a careful estimate should be made of the specific 
gravity of platinum, in this pure state, after fusion, and after having sustained 
diminution by combustion for some time, in order that all impurities might be 
driven off. For this purpose we selected a brilliant globule of the metal, weighing 
73 grains; and, having previously extended it as much as possible by hammering, 
that every air bubble might be removed, its specific gravity was ascertained in 
distilled water at a temperature of 63° of Fahrenheit both by Professor Cumming, 
and by me, and found equal to 20°857. 
1 7 
