P L A 
P L A 
623 
PLA'TIA, a fmall ifland in the gulf of Engia: eigh¬ 
teen miles north-welt of Engia. 
PLATIAS'MOS, /. [Gr. ofirAoh«£«, I dilate, formed 
from wAalv?, wide.] A word ufed by l’ome authors to 
exprefs a fault in pronunciation, owing to a perfon’s 
opening his mouth too wide, and thence fpeaking indif- 
tinftly. Cole has plateafm. 
PLATI'C, acj. See the article Astrology, vol. ii. p. 
310. 
PLATICO'RIA, f. [Gr. of vrAalv?, wide, and xo^vj, 
pupil.] A word ufed by medical writers to exprefs a 
preternatural dilatation of the pupil of the eye, ufually 
owing to a paralytic diforder. 
PLATIL'LA (La), a mountain of Spain, a little to 
the north-weft of Molina;celebrated for its mines of copper. 
PLATI'NA. See Platinum. 
PLATI'NA (Bartolommeo), an hiftorian and man of 
letters, was born in 1421 at Piadena (Platina) in theCre- 
monefe, from which place he chofe to take his furname, 
rather than Irom that of his family, which was De Sctcchi. 
He bore arms for fome time before he engaged in literary 
fludies, which he is fuppofed firft to have purfued at 
Mantua. Having made himfelf known to Cardinal Fran- 
cefco Gonzaga, he'accompanied him to Rome, where 
Pius II. aggregated him to his new College of Abbrevi- 
ators. Of this poll, which appears to have been his prin¬ 
cipal fupport, he was deprived by Paul II. who diffolved 
the college, and turned adrift leventy learned men em¬ 
ployed in it. See Paul II. vol. xix. p. 404. A recom- 
pence was made to Platina for his fuflerings by Sixtus IV. 
who, in 1475, gave him the honourable poll of keeper of 
the Vatican library, which he held till his death in 1481. 
Of the high efteem and reputation he had acquired among 
the learned in Rome, a proof is given in the diary of 
Jacopo Volterrano, who defcribes at length a folemn 
commemoration of the anniverfary of his death, in the 
following year, at that capital. 
_ Platina was one of the ableft fcholars of his time. Of 
his writings, his “Lives of the Roman Pontiffs,” com- 
pofed in Latin with a degree of elegance and energy then 
uncommon, is the moft celebrated. It was one of the firft 
pieces of biographical hiftory which gave an example of 
good criticifm. He frequently examines, doubts, con¬ 
jectures, cites ancient documents, refutes errors, and 
fometimes, as might be expedted, commits them himfelf. 
His greateft fault is the partial acrimony with which he 
fipeaks of fome contemporary popes, among whom it may 
be well fuppofed that he does not fpare Paul II. Ano¬ 
ther of his works is a Latin “ Hiftory of Mantua from its 
Origin to the year 1464.” This is of little value for the 
earlier periods ; but, when he comes near his own time, 
his narrative is equally judicious and elegant, though he 
is taxed with partiality to the family of Gonzaga. It has 
been edited by Lambecius and Muratori. The latter 
editor has alfo publifhed a Latin Life of Nerio Capponi 
by the fame author, which is curious and valuable. Pla- 
tina’s other writings are chiefly Dialogues on points of 
moral philofophy, and fhort treatifes on mifcellaneous 
topics: among the latter is one on culinary fcience, dedi¬ 
cated to Cardinal della Rovere. Gen. Biog. 
PLA'TING, f. The art of covering bafer metals with 
a thin plate of filver, either for ufe or for ornament. It 
is faid to have been invented by a fpur-maker, not for 
Ihow but for real utility. The more elegant fpurs 
were made of folid filver; and, from the flexibility of 
that metal, they were liable to be bent by the flighted: 
accident. To remedy this defeat, a workman at Bir¬ 
mingham contrived to make the branches of a pair of 
fpurs hollow, and to fill that hollow with a (lender rod of 
lied or iron. Finding this a great improvement, and 
being defirous to add cheapnefs to utility, he continued 
to make the hollow larger, and of courfe the iron thicker 
and thicker, till at laft he difcovered the means of coating 
an iron fpur with filver in fuch a manner as to make it 
equally elegant with thofe which were made wholly of 
that metal. The invention was quickly applied to other 
purpofes ; and to numberlefs uteniils which were formerly 
made of brafs or iron are now given the ftrength of thefe 
metals, and the elegance of filver, for a fmall additional 
ex pe nfe. 
The filver plate is generally made to adhere to the 
bafer metal by means of folder; which is of two kinds, 
the foft and the hard, or the tin and filver folders. The 
former of thefe confifts of tin alone, the latter generally of 
three parts of filver and one of brafs. When a buckle, 
for inltance, is to be plated by means of the foft folder, 
the ring, before it is bent, is firft tinned, and then the 
filver plate is gently hammered upon it, the hammer 
employed being always covered with a piece of cloth. 
The filver now forms, as it were, a mould to the ring, 
and whatever of it is not intended to be ufed is cut off. 
This mould is faftened to the ring of the buckle by two 
or three cramps of fmall iron wire; after which the 
buckle, with the plated fide undermoft, is laid upon a 
plate of iron fufficiently hot to melt the tin but not the 
filver. The buckle is then covered with powdered refin 
or anointed with turpentine; and, left there fliould be a 
deficiency of tin, a fmall portion of rolled tin is likewile 
melted on it. The buckle is now taken off with tongs, 
and commonly laid on a bed of fand, where the plate and 
the ring, while the folder is yet in a ftate of fufion, are 
more clofely compreffed by a fmart ftroke with a block of 
wood. The buckle is afterwards bent and finiflied. 
Sometimes the melted tin is poured into the filver 
mould, which has been previoufly rubbed over with fome 
flux. The buckle ring is then put among the melted tin, 
and the plating finiflied. This is called by the workmen 
filling up. 
When the hard folder is employed, the procefs is in 
many refpefts different. Before the plate is fitted to the 
iron or other metal, it is rubbed over with a folution of 
borax. Stripes of filver are placed along the joinings of 
the plate ; and inftead of two or three cramps, as in the 
former cafe, the whole is wrapped round with fmall wire ; 
the folder and joinings are again rubbed with the borax, 
and the whole put into a charcoal fire till the folder be 
in fufion. When taken out, the wire is inftantly removed, 
the plate is cleaned by the application of fome acid, and 
afterwards made fmooth by the ftrokes of a hammer. 
Lately, however, a mode has been invented of plating 
upon ingots of copper, and forming the utenfils out of 
the flieets and wire made from the ingots. This praffice 
is at prefent carried on to an immenfe extent in Shelfield, 
and alio at Birmingham, but on a fmaller fcale. The 
inventor of this method of making plated articles was 
not aware of its great importance. He began by making 
it into fnuff-boxes, and other trifling articles. It after¬ 
wards was extended to the manufaflory of pints and tan¬ 
kards, and other articles, by a Mr. Hancock, who erefled 
a mill near Sheffield for rolling the ingots. 
The crucibles are thofe made at Chelfea with black-lead. 
The ingot-moulds are of caft-iron, confining of two 
pieces, faftened together by two rings, with wedges, the 
interior being of the fhape of a parallelepipedon, about 
three inches broad, ii- in thicknefs, and about eighteen 
or twenty long. The mouth-piece, into which the metal 
is poured, makes an angle with the length of the cavity; 
fo that, when the mould is placed on the ground, with 
the narrow fide uppermoft, and makes an angle with the 
horizon ofabout ten degrees,the mouth-piece pointsdireft- 
ly upwards. The inclination of the mould and the length 
of the mouth-piece are to give a certain head of liquid 
metal, which determines the impurities of lefs fpecific 
gravity than the metal to rife into the cavity of the mouth¬ 
piece, in order to inlure the foundnefs of the ingot. If 
this were not attended to, the flieets rolled from fuch 
ingots would abound with feams and loofe places. It is 
eafy to fee that a fmall hole in the ingot would be the 
3 fource 
