G27 
P L A 
lamp ; and four or five coils fliould be placed on the wick, 
and the remainder of the wire above it; and which will 
be, as before faid, the part ignited. A wick, compofed of 
twelve threads of the ordinary-fized lamp-cotton yarn, 
with the platinum-wire coiled round it, will require about 
half an ounce of alcohol to keep it alight for eight hours. 
A flightly acid fmell, rather pleafant than otherwife, is 
yielded by this lamp during its ignition, arifing from the 
decompofition of the alcohol; as is alfo the cafe with 
ether. But camphor may be fubftituted for the alcohol, 
by introducing a cylinder of it in the place of the wick : 
in this cafe the ignition is very bright, and a very plea¬ 
fant odorous vapour arifes from it. 
This lamp without flame has been exhibited in Dr. 
Wilkinfon’s and Dr. Clarke’s lefture-rooms, at Bath and 
Cambridge; and is now fold by Carey, in the Strand, and 
other philofophical inftrument makers, at fix (hillings. 
Monthly Mag'. May, 1818. 
In the Phil. Tranf. for 1820. Part I. we have a paper, 
“ On fome Combinations of Platinum, by Edmund Davy, 
efq. profefl'or of chemiftry, and fecretary to the Cork In- 
ftitution.” This paper contains the refults of profefl'or 
Davy’s farther labours on the combinations of platinum, 
fince his former communication to the Royal Society in 
1817. The fubjeift of the experiments was a peculiar 
compound of platinum, obtained from fulphate of plati¬ 
num by the agency of alcohol. Unlike other fulphates, 
this is foluble in ether and in alcohol; and, by boiling 
for a few minutes, a black fubftance is precipitated, of 
a compofition and with properties not hitherto known. 
This new fubftance appears to confift almoft folely of 
platinum, with a little oxygen, and the elements of the 
nitrous acid. We mutt alfo mention the curious experi¬ 
ment in which the powder is brought in contact with the 
vapour of alcohol at the common temperature of the air, 
when there is an immediate chemical affion. The heat 
generated is fufficient to reduce and ignite the metal, and 
to continue it in a flare of ignition till all the alcohol is 
confumed. In this cafe the acid firft noticed by fir H. 
Davy (in his beautiful experiment of the ignited plati¬ 
num-wire) is produced. Hence the ufe of this powder 
for producing light and heat. By merely fprinkling the 
powder on any porous fubllance, as a fponge, cork, (and, 
&c. moiliened with alcohol, it immediately becomes red- 
hot, and fo remains till all the fpirit is confumed. Hence 
alfo the obvious ufe of this new fubftance as a fort of tin¬ 
der-box. 
We muft likewdfe take notice of the ufe of fulphate of 
platinum as a teft of gelatine, fince it feems preferable to 
other re-agents, efpecially to the moft delicate that is in 
ufe, tannin: for it appears that quantities of gelatine too 
(mall to be detected by tannin were rendered evident by 
fulphate of platinum; and that farther, a quantity too 
minute to be denoted by this fulphate in the cold became 
vifible on boiling. The author details a number of pro¬ 
perties of a grey oxyd of platinum, and of its compofi¬ 
tion ; but for thefe we muft refer to the memoir itfelf, 
which is worthy of the family of the Davys. 
Dr. Thomfon concludes, from the heft experiments 
that have been made on this metal and its compounds, 
that the weight of its atom is zz6'2^. 
PLAT'NA, or Pla'ten, a frnall town in the north of 
Bohemia, on the confines of Saxony, with manufactures 
of tin and iron. 
PLAT'NER (John Zachariah), an able phyfician, was 
born at Chemnitz, in Mifnia, in Auguft 1694.. His fa¬ 
ther, who was one of the principal merchants of the 
place, intended to make him his fuccefi'or in the fame line; 
but refolved to enlarge his mind hy a liberal education, 
and to give him a knowledge of ancient languages and 
philofophy, before he led him into commercial purfuits. 
But young Platner poflefled a delicate conllitution ; and, 
partly on this account, and partly in confideration of the 
rapid' progre(s which he made in his ftudies, his parents 
relinquifked their original defign, and confented that he 
P L A 
(hould direft his attention to medicine, for which he had 
manifefted a ftrong inclination. He repaired therefore 
to Leipfic in 1712, where he purfued his ftudies for the 
fpace of three years, when the reputation of the univer- 
fity of Halle induced him to vifit its fchools. During the 
following winter, he ftudied mineralogy and metallurgy 
in the celebrated mines of Chemnitz ; after which he re¬ 
turned to Halle, and received the degree of dodfor in 
September 1716. The purfuit of profeflional knowledge 
became his pafflon, and hefpent four years in vifiting the 
moft celebrated feats of learning in Europe. At Paris he 
particularly attended to anatomy and furgical operations, 
efpecially to thole relative todifeafes of the eye, in which 
lie is faid by Haller to have acquired fuch dexterity, as to 
have fucceeded in the cure of fome which the celebrated 
St. Ives had failed to relieve. 
He now determined to fettle at Leipfic, and accord¬ 
ingly fixed himfelf in that city in 1720; and his great 
profeflional acquirements werefpeedily rewarded by pub¬ 
lic acknowledgments of their value. In 1721 he was ap¬ 
pointed profefl’or extraordinary of anatomy and furgery; 
in 1724 lie obtained the cha'ir of phyfiology, which had 
become vacant by the death of Rivinus ; in 1737 he was 
promoted to the profeflbrfhip of pathology, and in 1747 to 
that of therapeutics. He was alfo nominated perpetual 
dean of the faculty, and confulting phyfician to the court 
of Saxony. He did not live long, however, to enjoy thefe 
flattering diftinftions; for he was carried off fuddetily, on 
the 19th of December, 1747, in the fifty-fourth year of his 
age, by a paroxyfin of afthma. He had vifited his pa¬ 
tients on the morning of that day, and given his lecture 
after dinner;'and upon returning home, about fix in the 
evening, was feized with the fatal fit. 
He left only three different works, the firft of which, 
entitled “ Inftitutiones Chirurgite Rationalis, turn inedi- 
cae, turn manualis,” Leipfic, 1745. was publifhed by him¬ 
felf. It pafl’ed through feveral editions. The fecond, 
“ Opufculorum Chirurgicorum et Anatomicorum Tomi 
duo: Diflertationes et Prolufiones, 1749,” was edited by 
his fon, Frederic Platner, a profefl’or of law. And the 
third, “ Ars medendi fingulis niorbis accommodate,” 
1765, which had been bequeathed by the author to his 
pupil J. B. Boehmer, upon condition that it fliould not 
be pubiilhed, was printed by a bookfeller, Fritfch, into 
whofe hands a copy of it fell eighteen years after the 
author’s death. Eloy Did. de la Med. 
PLA'TO,a Greek comic poet, born about the year 455, 
B. C. and was contemporary with Ariftophanes and Euri¬ 
pides. He was corilidered as at the head of the middle 
comedy, ,pnd is faid by Suidas to have left twenty-eight 
compofition9 of this clafs. The titles of many are extant 
in Athenasus, Pollux,and other writers ; and lie is fpoken 
of as an author of high reputation. Ariftophanes and he 
were charged with reciprocally borrowing from each 
other, which indicates a parity of public eftimation. Of 
his works, only a few fragments are preferved, fome of 
which are of the epigrammatic kind. See Cumberland's 
Ob fewer, N° 78. 
PLA'TO, one of the moft iliuftrious Grecian philofo- 
phers, and founder of the academic feff, though an Athe¬ 
nian by defcent, was born in the ifland of iEgina, where 
his father refided after that ifland had become fubjedt to 
Athens. He was of exalted origin; his father Arifto 
being a defcendant from Codrus, and his mother Peric- 
thione from Solon. Concerning the time of his birth 
there is a final 1 difference of opinion among the chrono- 
logifts; fome placing in the firft year of the eighty-eighth 
Olympiad, and others, perhaps with more accuracy, in the 
third year of the eighty-feventh Olympiad, or 430 B. C. 
His parents at firft called him Aristocles, after his 
grandfather; but afterwards his name was changed for 
that of Plato, which was given him on account of the 
great breadth either of his (boulders or forehead. 
As he afforded early indications of a bright and promif- 
ing genius, due care was taken that he (hould enjoy the 
advantages 
