*ruR
TU R
( 4 52 )
through which it has {trained, together withthe coarfe {trainings, chips of bark {baked inturpentine, the broken earth of the moulds inwhich the refin collects, &c. kindling it till allthe refin falls down into a refervoir, and con-tinuing the heat till it is fufficiently infpifiated.This forms a hard black mafs called Poix dureor Pfgle-
The pitch made in this country by boilingdown tar to the proper confillence, is now per-formed near London , and in fome other parts,in a {till with a worm-tub attached to it, in or-der to collect the valuable volatile products ofthe tar. The procefs is the following: 15 thebarrels of tar being of various confillence, theircontents are firft emptied into a copper, andgently heated and well birred, to render themthin and uniform. The tar is then laded intothe Hill, palling through a fieve to keep outchips of wood and other impurities.
When the {till is properly luted, the fire iskindled and kept up very moderate for threehours, as the tar is very apt to boil up in theearly part of the procefs. The firft produdt thatdiftiils over is principally a brown acid water,mixed however with a good deal of oil. As theprocefs advances, and the heat is increafed, thequantity of acid leffens, and that of oil increafes,and towards the end of the diitillation the pro-du£t is chiefly oil. The length of the procefs■Varies according to the quality and hardnefs ofthe pitch required. In general a bill that holdsabout 600 gallons will work 18 or 20 barrelsof tar in 8 hours, the produce of which will beabout 10 barrels of pitch (or 22 cwt.), 176gallons of oil; and about 40 gallons of acid.The pitch remains in the {till for 12 hours,after which it is barrelled, and hardens as itcools.
The oil and acid water which diftill overdo not mix, fo that they may be eafily feparatedby decantation. The oil is a brownifh inferiorkind of oil of turpentine, which is very ufefulin painting {hips and other coarfe out-door work.The acid is a very ftrong brownifh empyreumaticacid, which appears very clofely to refemble thepyroligneous acid obtained from the diftillationof wood during its converfion to charcoal, andis now employed pretty largely in compofingfevera! of the mordants in callico printing.
TURPENTINE (Clio.)
This is a very fragrant refin, obtained fparing-ly by incifion of the bark of the Pijlacia Tere-binthus, a fmall tree growing in the Ille of Chio,and in many other parts of the Levant.
It is a thick and tenacious fubftance, whitifh,nearly tranfparent, highly fragrant, and almofttaftelefs. It is feldom found genuine, the com-mon Chio turpentine of the {hops being largelyadulterated with the finer forts of the pine tur-pentines.
TURQUOISE.
The colour of this fubftance is pale lky-blue,paffing into indigo-blue and pale apple green.It occurs in mafs or difleminated. Its fractureis even. Its hardnefs is nearly equal to that ofglafs ; it is difficultly frangible. Sp.gr. 3.12.
Before the blowpipe its colour changes togreyifh white, and it becomes friable, hut doesnot melt. It is foluble in nitro-muriatic acid,and the European varieties are fo in nitric acid;this menftruum however has no action on thePerfian turquoifes. It is compofed, accordingto Buillon La Grange, of
80 Phofphat of lime8 Carbonat of lime2 Phofphat of iron, with a traceof manganefe2 Phofphat of magnefia1 Alumine6 W ater and lofs
99
Turquoife is generally confidered as foffilbone, or ivory penetrated by oxyd of copper ;it appears, however, from the above analyfis,that the colouring matter is phofphat of iron.The oriental turquoifes are found near Meched in Perfia, alfo in Mount Caucafus, in Egypt and Arabia. The occidental ones are found inLanguedoc in France, and in Hungary . Tur-quoife was formerly in fome eftimation for ringsand other articles of perfonal ornament, but itsvalue has greatly declined in modern times.The colour of turquoife changes gradually byexpofure to the air, from blue to green : when itarrives at this ftate its commercial value i*wholly extin£t.
TUTENAG. See Copper, alleys of.
> Original Commiinicatien.