LABORATORY. The workshop of a chemist. Some laboratories are intended for private research, and some for the manufacture of chemicals on the large scale. Hence it is almost impossible to give a description of the apparatus and disposition of a laboratory which_ would be generally true of all. A manufacturing labOratory necessarily occupies a large space, while that of the scientific man is necessarily limited to a peculiar line of research. Those who study in organic chemistry have different arrangements from that of the mineral analyist.
A laboratory is furnished with a fixed furnace, and sundry auxiliaries and por table furnaces. It ought also to contain blow-pipes and galvanic troughs, with crucibles, matresses, retorts, flasks, ves sels, and bottles ; also a pestle and mor tar, a vice, a lathe, and carpenters tools ; a pneumatic trough, a sink for water, ta bles, drawers, and shelves; with thermo meters, a barometer, pyrometer, hydro meter, Argand's lamps, Wollaston's scale, weights and measures, &c. It requires also a small stock of tests and test-paper, and of sulphuric, nitric, and acetic acids ; with nitre, soda, ammonia, alcohol, &c., &e. ; and especially pasteboard and. wire masks, and a stout apron for the stomach and abdomen. The cost varies from $200 to $2,000.
The expense of fitting up a laboratory to furnish articles of common consump tion is very small. The instruments in dispensably necessary are—an alembic, with a refrigerator and portable furnace. If the operator should not choose to go to the expense of the alembic and its ap paratus, a succedaneum may be found for them in a sand-bath or sand-heat, with retorts, under suitable precautions. Sand-heat is usually formed, in the large of an oblong shape, having bricks and mortar for its walls, plates of iron upon which to lay the sand; and around the top a ledge, of about six or eight inches deep, of free-stone, to retain the sand. Beneath the plates of iron is a wide flue, at the bottom of which is an non grating, upon which grating is laid • the fire. The fire is, of course, when
kindled, enclosed by a door, as in other furnaces, at the end of the sand-heat ; a flue communicates with a chimney, to carry off the smoke. The sand is com monly of the depth of six or eight inches ; but the quantity and depth depend upon the size of the vessels.
A retort is a vessel usually made of green or other glass, and may be made to hold from half a pint to eight or more gallons. It has a long narrow neck, which is so bent, that when the retort is placed with its contents in a sand-bath, or over a fire, it has a gentle inclination, and will conduct whatever liquid is con densed in it, into a glass receiver, which is placed on a bench beside the sand-heat ; the receiver is luted to the neck of the retort, either by a caoutchoue skin, which is the neatest way, or by some other lute. A variety of chemical processes are than conducted : the vapors raised by the heat being condensed in the neck of the re tort, and cooled down in the receiver, (which is usually about the size of a rs tort,) by the large surface which it pre sents to the air. With Florence flasks and bent tubes fitted with cork many opera tions requiring retorts may be used; and even small glass tubes may supplant these latter in the more delicate applica tions.
On this, as on many other subjects, more is learnt in half an hour, by actual inspection, than by half a volume of de scription.
There are some very well-appointed laboratories in this country ; amongst others, that in the Lawrence Scientific School, Harvard University, Cambridge, Mass., and those in Philadelphia are pro minent.
LAC. Lac-dye, is produced by the puncture of an insect called the Coons Lacca, upon the branches of several plants as varieties of the ficus, rhamnus, and the eroton. It is the female insect which punctures the twig, which then becomes surrounded with a resinous juice which hardens and has a crystalline fracture. This constitutes the stick-lac of commerce ; it is of a red color, more or less deep and transparent.