160 



CHEMISTRY. 



M ' k 



e-XLiii. 



fig. S. 



rig . IO.M, 



Kg. 12. 



Fig. is. 



Crucibles. 

 Pip. M, 

 15, 16, 17. 



ing* are furnMird with thick brick (topper* and iron 

 plates which slide over their. There are two opening* 

 66 in the nh pit, which serve to regulate the draught of 

 air, and, of course, to vary the heat of the furnace. 



Fig. 9 it a muffle. This i* a vaulted flat-bottomed 

 earthen vessel, close at one end nd open at the other. It 

 i* introduced into a furnace with its open end corre- 

 sponding to the muffle door of the furnace, and is intend 

 ed to expose small vessels to heat without being in con- 

 tact with the fuel. Then- are usually openings in its 

 (ides to allow the entrance of heated air. 



1 i ures 10. and 11. represent a convenient and cheap 

 blast furnace, contrived by Mr Arthur Aikin from an 

 idea of Dr Lewi* in his Philosophical Commerce of the 

 Art*. It consists essentially m two black lead crucibles, 

 one of which a is inverted, and the other b is placed over 

 it. A hole is bored in the bottom of the crucible b, in- 

 to which the clay stopper c (Fig. 12.) is fixed, merely 

 to give firmness. Eight holes are bored in the bottom 

 of the crucible b, only two of which are represented in 

 the Figures. Through these holes the air driven in by 

 the beUows, represented in Fig. 10. fixed upon a wood- 

 en stand, makes its way to the fuel, and speedily raises 

 a most intense heat. To protect the eyes, it is often ne- 

 cessary to put the crucible c, Fig. 13. furnished with the 

 opening^/*, to let out the smoke, over the crucible b. 



Figures I*, 15, 16, 17, represent two crucibles, the 

 one triangular, the other circular, with their lids and 

 their supports. These supports are sometimes rolled, 

 as in Fig. 40, and sometimes hollow as in Fig. 11. Cru- 

 cibles are made of a very refractory clay. The Hessian 

 crucibles are upon the whole the best. The black lead 

 crucibles, made in England, are likewise excellent. They 

 bear sudden heating and cooling well, and they are so 

 soft that they can be conveniently cut with a knife, or 

 taw any way that the experimenter pleases. Of late it 

 is said that micaceous iron ore, or some similar ore of 

 iron, has been substituted for black lead by the manu- 

 facturers. This is a grievous fraud, and injures the va- 

 lue of the crucible* most materially. Cast iron cruci- 

 bles are sometimes used by chemists, but they are not of 

 much value. Crucibles of fine silver are indispensible 

 for the analysis of stony bodies, as silver best resists the 



action of alkaline bodies at hightemperatures. Crucibles Chemical 

 of platinum are also indispensible in a good laboratory. Apparatu 

 They bear almost any temperature, and are but little ^v^ 

 acted on by most chemical agents. 



Mortars of various kinds, for pounding solid bodies, Mortat*. 

 are aUo necessary for the laboratory. There should be 

 one of glass, one of Wedgewood ware, and one of agate. 

 There should also be one of steel, consisting of a hollow 

 cylinder fitted into a flat steel piece. A solid steel cy- 

 linder should be fitted by grinding into the hollow cy- 

 linder. The hard stone (ruby, Tor example, ) is to be 

 put by little at a time into this mortar, and, by a smart 

 blow with a hammer upon the solid cylinder, it is easily 

 reduced to small fragments. These are ground to an 

 impalpable powder in the agate or flint mortar. The 

 readerwill find figures of different mortars, searces, and va- 

 rious other utensils, as files, &c. which we do not think 

 it worth while to mention, in Lavoisier's Elements oj~ 

 C/iemistry. 



It may be worth while to say a few words about lutes, Lute. 

 which are essential to the practical chemist. Flour, al- 

 mond-meal, or linseed-meal, make a good enough lute 

 for a common still. They are made into a paste, ap- 

 plied when moist, and allowed to dry. The fat lute an- 

 swers well for luting retorts and receivers. It is made 

 by beating together pipe-clay and lineed-uil. As it ne- 

 ver becomes hard, it is requisite to cover it with linen, 

 and tie the whole firm with a string. The best way is 

 to dip the linen into a hot solution of glue ; and to allow 

 the linen to dry after it has been tied on, before begin- 

 ning the distillation. For coating glaso retorts, a mix- 

 ture, of pipe-clay, sand, horse-dung and glue, made into 

 a thin paste, answers well. The retort is dipped in, and 

 after the first coating is dry, it is dipt again. This is 

 continued till the coating is sufficiently thick for the 

 purpose required. A very good lute for those joinings 

 that arc to be exposed to a strong heat is a mixture of 

 clay and borax. We have also used successfully a mix- 

 ture of clay, sand, and litharge. But this last lute is 

 not so much to be depended on. Many other lutes are 

 to be found in chemical books j but those we have men- 

 tioned are the ones which upon trial we have found 

 best.* (c) 



For this valuable article on CHEMISTRY, the Editor has been indebted to THOMIS THOMSON, M.D. F.H.S. London and Edin- 

 kurgk. 



INDEX. 



