FLA 
FLA 
plates are the two plates on the face of the 
carriage, one on each cheek. Train-plates 
are the two plates on the cheeks, at the 
train of the carriage. Dulidge-plates are 
the six plates on the wheel of a gun-carri- 
age, where the felloes are joined together, 
and serve to strengthen the dulidges. 
PLATFORM, in the military art, an ele- 
vation of earth, on which cannon is placed, 
to fire on the enemy ; such are the mounts 
in the middle of ciirtins. On the ram- 
part there is always a platform, where the 
cannon are mounted. It is made by the 
heaping up of earth on the rampart, or by 
an arrangement of madriers, rising insensi- 
bly, for the cannon to roll on, either in 
a casemate, or on attack in the out-works. 
All practitioners are agreed, that no shot 
can be depended on, unless the piece can 
be placed on a solid platform ; for if the 
platform shakes with the first impute of the 
powder, the piece must likewise shake, 
which will alter its direction, and render the 
shot uncertain. 
Platform, in architecture, is a row of 
beams, which support the timber-work of a 
roof, and lie on the top of the wall, where 
the entablature ought to be raised. This 
term is also used for a kind of terrace, or 
broad, smooth, open walk at the top of a 
building, from whence a fair prospect may 
be taken of the adjacent country. Hence 
an edifice is said to be covered with a 
platform, when it is flat at top, and has no 
ridge. Most of the oriental buildings 
are thus covered, as were all those of the 
ancients. 
PLATINA, or Platinum, a metal, 
which in most of its properties is equal to 
gold, but in others it is very superior. It 
was first ascertained to be a distinct metal 
by Scheffer, a Swedish chemist, in the year 
1752. By him it was named white gold, 
because it resembled this metal in many of 
its properties. It immediately became 
subject to the experiments of all the che- 
mists in Europe, and obtained, from its co- 
lour, the name of platina, signifying little 
silver, from the word plata, which is 
Spanish for silver. Platina has been 
found among the gold ores of South Ame- 
rica, and more particularly in the mine 
of Santa Fe near Carthagena, and in the dis- 
trict of Choco in Pern. Platina, in the 
state in which it reaches this country, is 
contaminated by the presence of several 
other metals, as iridium, osmium, rhodium, 
and palladium, and, in fact, it is merely an ore 
of platina. It is in the form of small grains 
or scales, of a whiter colour tlian iron, and 
extremely heavy. A^arious, processes have 
been contrived for its purification ; but the 
one, which is the most simple and practica- 
ble, is described in the ninth volume of Ni- 
cholson’s Joulnal. Platina has the follow- 
ing properties. It is a white metal, re- 
sembling silver in colour, but greatly ex- 
ceeding it, and indeed all other metals, in 
specific gravity, being, when it is hammer- 
ed, twenty-three or twenty-four times hea- 
r ier than water. It is not oxydized by the 
long-continued and concurrent action of 
heat and air. It has the property of welding, 
which belongs to no other metal but this and 
iron. It is not acted on by any other acid 
than the nitro-muriatic and oxygenized mu- 
riatic. The former is best adapted to effect 
this solution. Sixteen parts of the com- 
pound acid are to be poured on one of the 
laminated metal, and exposed to heat in a 
glass vessel ; nitrous gas is disengaged, and 
a reddish coloured solution is obtained, 
which gives a brown stain to the skin. The 
muriate of platina has the characteristic 
property of being precipitated by a solution 
of muriate of ammonia. By this character, 
platina is distinguished from all other me- 
tals, and may be separated when mingled 
with them in solution. The precipitate, 
thus obtained, is decomposed by a strong 
heat, and leaves pure platina. AFhen pure 
potash is poured into the muriatic solution, 
a precipitate ensues, which is not an oxide 
of filatiua, but a triple compound of that 
oxide with the alkali and acid. With soda, 
also, it forms a triple combination. 
Platina is acted upon by fusion with ni- 
trate of potash, and also with pure fixed al- 
kalies. The most delicate test of the pre- 
sence of platina is muriate of tin. A solution 
of platina, so dilute as to be scarcely distin- 
guishable from water, assumes a bright red 
colour, on the addition of a single drop of 
the recent solution of tin. 
Platina has been discovered by Dr. Wol- 
laston to be a remarkably slow conductor 
of caloric. When equal pieces of silver, 
copper, and platina, were covered with 
wax, and heated at one end, tlie wax was 
melted inches on the silver ; 2^ on the 
copper, and one inch only on the platina. Its 
expansion by heat is considerably less than 
that of steel ; whiqh, between the tempera- 
tures of 32“ and 212° is expanded about 12 
parts in 10,000, while the expansion of pla- 
tina is only about 10. 
Platina combines with many of tlie me- 
tals, and forms with them alloys, some of 
