744

LAMPATES.

a defect in its principle, or even in the rules for its practical application, as laid down MSir Humphrey—I maintained that ‘ the Davy’ approximated perfection, as nearly as a rsjinstrument of human invention could be expected to do. We have ascertained distinctlythat the late explosion did not happen in that part of the mine where the Davys wereused. They were all found in a perfect state after the accident—many of them inhands of the dead bodies of the sufferers.”

LAMP-BLACK. See Black. . v

LAMPATES and LAMPIC ACID. When a spirit of wine lamp has its cotton wi®surmounted with a spiral coil of platinum wire, after lighting it for a little, it may "blown out, without ceasing to burn the alcohol; for the coil continues ignited, and a cut'rent of hot vapor continues to rise, as long as the spirit lasts. This vapor was first con-densed and examined by Professor- Daniell, who called it lampic acid. It has a peculi ar >strongly acid, burning taste, and a spec. grav. of 1-015. It possesses in an eminent de-gree the property of reducing certain metallic solutions; such as those of platinum, g°} ’and silver. The lampates maybe prepared by saturating the above acid with the alkaband earthy carbonates. j

LAPIDARY, Jlrt of. The art of the lapidary, or that of cutting, polishing,engraving gems, was known to the ancients, many of whom have left admirable speciB 1 ^of their skill. The Greeks were passionate lovers of rings and engraved stones; and 1most parsimonious among the higher classes of the Cyrenians are said to have worn ringof the value of ten minae (about 301. of our money.) By far the greater part of the anMgems that have reached modern times, may be considered as so many models for form ^the taste of the student of the line arts, and for inspiring his mind with correct ideaswhat is truly beautiful. With the cutting of the diamond, however, the ancients wunacquainted, and hence they wore it in its natural state. Even in the middle ages, dart was still unknown; for the four large diamonds which enrich the clasp of the imP e *jmantle of Charlemagne , as now preserved in Paris , are uncut, octahedral crystals,the art of working diamonds was probably known in Hindostanand China, in -v-ery re TS, e jrperiods. After Louis de Berghen’s discovery, in 1476, of polishing two diamonds by 1mutual attrition, all the finest diamonds were sent to Holland to he cut and polish® :the Dutch artists, who long retained a superiority, now no longer admitted by the I®Pries of London and Paris . cU t-

The operation of gem cutting is abridged by two methods; 1. by cleavage ; 2. W f ating off slices with a line wire, coated with diamond powder, and fixed in the sl0 ,. ffl0 ndhand-saw. Diamond is the only precious stone which is cut and polished with diampowder, soaked with olive oil, upon a mill plate of very soft steel. . 0 j; v e

Oriental rubies, sapphires, and topazes, are cut with diamond powder soaked withoil, on a copper wheel. The facets thus formed are afterwards polished on anotherper wheel, with tripoli, tempered with water. at a

Emeralds , hyacinths, amethysts, garnets, agates, and other softer stones, are cu ^lead wheel, with emery and water; and are polished on’a tin wheel with trip 01water, or, still better, on a zinc wheel, with putty of tin and water. r j^d

The more tender precious stenes, and even the pastes, are cut on a mill-wheel o ^ e jwood, with emery and water; and are polished with tripoli and water, on anotherof hard wood. . ^ cn ts

Since the lapidary employs always the same tools, whatever be the stone whichor polishes, and since the -wheel discs alone vary, as also the substance he uses wi ,_ cU t-we shall describe, first of all, his apparatus, and then the manipulations for diamting, which are applicable to every species of stone. : s ( S of

The lapidary’s mill, or wheel, is shown in perspective in fig. 616. It c01 ?..." with616 a strong frame made of oak carpen ^g e ther

tenon and mortised joints, its^

with strong bolts and screw nut.. ^ py

is a parallelopiped of from 8 to 9‘ e jj-oad-from 6 to 7 high; and about ~ t0These dimensions are large en0 ?f 0 flain two cutting wheels alongsiother, as represented in the figure. ce jveBesides the two sole bars B n, ^ c-in the breadth, 5 cross bars, > ^ j, a rt o<

The two extreme bars c and e, a Thf

and serve to bind > U ,eand r, carry ^ #

(see Jig. 617), joined solid’y by mortises

COfl-

ead 1

the frame-worktwo cross-bars i>

middle of their length, a P iec ., ; nc ]ies i‘thick as themselves, but only * aS well«»wi *-tKui rroSS

Ion?

as