this kind should never be exposed to the direct fire, but only to the heat of the water-bath, to prevent the metal from fusing and the contents from getting charred. The water-bath consists of a copper boiler, in which the still is fitted so as to reach nearly to the bottom, while resting rather lightly on the prominent edges of the contracted mouth of the boiler.

The tin still serves for extractions and distillations (see F.) on a larger scale.

E.-STRAINING APPARATUS.

For larger quantities dishes or deep vessels of porcelain or stoneware are used with a tenaculum (square framework, constructed of four narrow pieces of wood) of proper size to be placed on the dishes, and carrying on its four prominent points a linen cloth or a linen bag-filter, through which to strain the substance under investigation. The latter operation is accelerated by occasionally stirring or pressing the contents with a strong glass rod or with a porcelain spatula, or instead of these a spatula, made of pine or beech and previously cleaned by boiling with water, suffices for most purposes.

Thick, slimy masses let the liquid pass so slowly that it is necessary to strain through a cloth, the meshes of which do not contract by moisture. This is miller's gauze, or bolting cloth of silk, which is sold in numerous gradations as to the width of the meshes, and may be therefore selected according to circumstances.

After the dripping has ceased, the contents of the cloth or of the bag-filter are submitted to the action of a screw-press or of an hydraulic press. Those parts of the press, which are in direct contact with the cloth or with the liquid passing from it, must be made of tin. For pressing smaller quantities, a small self-acting press, similar in construction to a bookbinder's press, is to be employed, but modified that it may be fastened to a table, and its sides must be covered with thick plates of glass.

Still smaller quantities are poured into paper-filters, spread out in funnels of glass or porcelain, the latter resting on the edges of glass-jars, and, if necessary, supported by means of filter-plates or other appliances. If the filtering process is slow, the funnel must be covered with a glass-plate in order to screen off air and dust. This is not less necessary with very volatile liquids, for instance, alcohol, ether, &c., in order to prevent losses.

More economically, larger quantities or slowly filtering alcoholic liquids are filtered in a displacement apparatus of glass, the top of which can be shut nearly air-tight.

For the filtration of liquids, which require warming either because they are then only of sufficient fluidity, or because in lower temperatures the solved parts would become solid, a water-bathfunnel is employed, i.e. a water-bath of funnel-shape and exactly

fitting to the funnel containing the filter, and the water of which is kept boiling by means of a tube inserted at the side, and heated by the flame of a lamp beneath.

F.-EVAPORATING APPARATUS.

Under this head have to be mentioned dishes of glass and of porcelain, also of tin (see below), watch-glasses, glass beakers of various sizes.

For accelerating the evaporation at higher temperatures, coals, alcohol or gas, are employed as fuel to act upon the evaporating vessel either directly or divided from it by an iron plate or a dish of the same metal, either empty or filled with sand (sand-bath), or with water (water-bath).

Should it be necessary to accelerate the evaporation without the application of heat, or under the exclusion of the atmosphere, the air-pump is made use of, and additionally the fluid to be evaporated under the receiver is brought in proximity with either concentrated sulphuric acid or anhydrous chloride of calcium or quicklime.

Some liquids leave, when concentrated to a certain degree, a stiff, viscid mass, to dry which entirely in the evaporating vessel is very difficult; but this may be effected with comparative ease by spreading those substances as thinly as possible on glass plates or on porcelain dishes. Plates of this kind are, among other instances, indispensable for any contents of filters, which may be expected on drying to stick to the paper, and thus prevent the separation without loss.

A kind of evaporation is the process of distillation. For this purpose on a larger scale, the tin-still mentioned already under D. is employed. Distillations of ether or of alcohol may be effected directly from it, but not those of water. For the latter purpose the still has to be furnished with a special contrivance. For instance, in order to obtain the volatile oil from a vegetable (including at the same time the extraction of the substance), a sieve-like perforated disc of tin and furnished, besides, with a larger aperture of about one inch diameter, is inserted into the still, within one to two inches from the bottom of the vessel. On this disc the vegetable substance, moistened previously with water, but not so as to form a pulp, is spread out, and is subjected to the steam of water coming from the copper boiler, and conducted by means of a tin tube, terminating under the false bottom, into the substance to be distilled. A mechanism of this kind, besides other implements intended for digesting, evaporating, drying, &c., purposes (dishes of tin, &c.), also a refrigerator, together with the tubes required for supplying the cold, and for removing the hot water, form the well-known Beindorf's apparatus.

Distillations on a smaller scale are carried on in retorts of glass, the vapours produced are condensed in a Goebel's refrigerator, and collected in glass receivers.

G.-MISCELLANEOUS APPARATUS.

Under this category I shall comprise the rest of the utensils, required for a phyto-chemical laboratory, but without any further description.

Aræometers for light and for heavy liquids.

Barometers.

Bladders.

Blowpipe.

Caoutchouc in tubes and in thin plates.

Caoutchouc cement, from heated indiarubber and kaolin.
Coal pincers.

Coal prepared for cutting glass.

Crucibles of porcelain and of platinum.

Florentine glass bottle.

Funnel-tubes.

Glass bottles with or without glass stoppers.

Glass jars, graduated.

Glass jars, to be fitted air-tight on glass plates.

Glass rods.

Glass tubes (including capillary tubes for determining the fusing

Stands of wood (for test tubes, retorts, thermometers, &c.).
Stoppers of glass, caoutchouc, cork.

Stoves of clay and of iron.

Test-paper of litmus and of turmeric.
Test-tubes.

Thermometers.

Thread of various thickness.

Tongues of iron and of brass.

Washing bottle for washing precipitates.

Wires of iron and of platinum.

DIVISION II.

CHEMICALS REQUIRED FOR PHYTO-CHEMICAL

ANALYSES.

THESE chemicals may be divided into—

A. Absorbents.

B. Solvents.

C. Reagents.

A.-ABSORBENTS.

These are principally: concentrated sulphuric acid, anhydrous chloride of calcium and quicklime.

They are used for drying a solid or liquid substance at ordinary temperature and under exclusion of the air, by placing them in a glass beaker close to the substance under the receiver of an air-pump, and by working the latter occasionally after intervals of two to three hours.

Every one of the three substances named has its special value. For quickness of action anhydrous lime is unsurpassed, and especially so, when it has been reduced to about the size of peas; but its power is soon exhausted, as it absorbs only 1 eq. water, equal to its own weight. Next in quickness acts concentrated sulphuric acid, which absorbs up to 3 eq. water, increasing its weight by one half. The slowest action is exercised by anhydrous chloride of calcium, but though the least powerful yet it absorbs 6 eq. water or nearly its own weight, and besides it takes up another quantity of water required to convert the compound Ca Cl + 6 HO into the liquid state.

By taking into account these different qualities, the choice of the absorbent cannot be difficult. Should it be required to conduct the drying process as quickly as possible, quicklime is resorted to; if less pressed for time, sulphuric acid; and if time is of no consequence, chloride of calcium. [There may be other considerations to guide in the choice of these absorbents.]

Besides these there are many other hygroscopic substances, but none exceeds in activity and cheapness the above three.

After they have done their service as desiccating agents, the chloride of calcium solution may be evaporated and fused again. The aqueous sulphuric acid may be utilised as such; and the hydrate of lime, as left, would be of no further value.

B. SOLVENTS.

These are principally ether, alcohol and water; also diluted acids (especially hydro-chloric and sulphuric), diluted alkalies (potash or soda-ley and liquor of ammonia); less frequently used are benzol, chloroform, wood-spirit, sulphide of carbon, petroleum, oil of turpentine, &c.

Ether withdraws from the plants, almost without exception, easily and completely chlorophyll, wax, fixed and volatile oils, free acids; also certain alkaloids, pigments, indifferent bitter ingredients, resins; sparingly or not at all saccharine substances. But even such compounds as are insoluble in pure ether, as humus substances, salts of anorganic acids, proteins, &c., dissolve, though in exceedingly small quantities, in ether containing traces of water or alcohol, and retard thereby the isolation of the first-named substances in their pure state.

This inconvenience might be avoided entirely or for the greatest part by using ether of 0-720 sp. gr. (at 15°), which is entirely free from water and alcohol.

Of greater consequence still than with ether is the strength of the alcohol (spirit of wine, ethylalcohol) employed as a solving agent. Absolute or anhydrous alcohol of 0.792 sp. gr. (at 15°) dissolves like ether readily chlorophyll, volatile oils, free acids, alkaloids, indifferent bitter substances, resins and pigments; less easily wax, fats and saccharine matters; sparingly humus substances, salts of anorganic acids and proteins.

Yet as it is troublesome to prepare and to keep alcohol in its anhydrous state, it is reserved for special cases, and in its stead an alcohol of 0.815 sp. gr. is generally in use, the solving power of which is nearly the same in regard to wax and fats, and is sometimes even greater towards the other substances mentioned. Unfortunately it also dissolves to some extent gum and similar matters, which have afterwards to be removed by special processes. It is not advisable to use weaker alcohol as a solvent, as this would prevent complete isolation of various constituents.

Dilute alcohol is employed in some cases for withdrawing resins from fats, or for separating different resins from each other.

For extracting purposes, spring or any other ordinary water should not be used but always distilled water, or, in exceptional