times used also for removing colouring matters, by assimilating those and rendering them insoluble. It serves also for separating fluid from solid fat-acids (see Part II., Div. III., A, a.)

White of lead may be used instead of oxyd of lead, and acts even more decidedly in many cases.

Acetate of magnesia (1 part in 9 parts water) serves sometimes for the fractional precipitation of solutions of soaps containing different fat-acids, in order to facilitate their separation.

Chloride of lime is used in its clear aqueous solution for bleaching the vegetable fibre (see Fibre, p. 82).

Lime, slaked with water as to form the finely pulverulent hydrate, serves only for displacing volatile alkaloïds (see Div. III., X.).

Phosphoric acid is employed for dissolving protein substances (see Div. III., IV.); also for displacing volatile organic acids (Ibid, IX.).

Sulphate of soda, Glauber's salt (1 part in 9 parts water), is employed for removing lead from liquids, when carbonates of alkalies have to be avoided; yet, as it does not precipitate the lead completely it is necessary, after filtering, to remove the rest of the lead by means of sulphuret of hydrogen.

Sulphate of silver (1 part in 200 parts water) is employed, before distilling the volatile organic acids, to remove hydrochloric acid. Sulphuret of hydrogen serves not so much for freeing the bases from any excess of lead-salts (for which purpose the carbonates or sulphates of alkalies are preferable) as for decomposing newly precipitated and edulcorated lead-precipitates with the view of isolating the acid combined with the lead. The gas obtained from sulphide of iron by means of diluted sulphuric acid has to pass through water in order to get rid of particles carried mechanically, before it comes in contact with the lead-precipitate. Animal charcoal, as finely ground bone-black purified by hydrochloric acid and heated afterwards to a red heat, is an important means for absorbing pigments, odours and bitter substances, and is even used for isolating the latter pure, by submitting the coal laden with them and after washing with water, to digestion with strong alcohol, which then withdraws the bitter substance or substances.

over

Alumina, in its newly precipitated hydrated state, may often be employed with advantage as separating agent, as it precipitates pigments and many other either little coloured or colourless bodies from their solutions and leaves others dissolved.

DIVISION III.

GENERAL SYSTEMATIC COURSE OF PHYTO-
CHEMICAL ANALYSIS.

ETHER, alcohol, and water, are, as recorded, the most important solvents, respectively extracting agents used in phyto-chemical analysis; acids, alkalies, &c., being of less importance.

In using the above three liquids, it would appear at first of little consequence in what order they are applied to the substance under investigation, as, after all, the parts soluble in them must enter these liquids as extracts; but taking into consideration all circumstances for the purpose, it soon becomes evident that a certain order has to be adhered to. Those special cases are of course excepted where it is required to obtain or to recognise only one constituent, and when the choice of the solvent depends already on the nature of the particular constituent, as for example, when ether is required for extracting a fixed oil, and water for gum. Still, if a thorough investigation of the chemical constitution of plants should be intended, then I would recommend to follow the practice adopted by me since many years,— to treat the substance first with ether, then with alcohol, and last with water, the reasons for which treatment I shall give presently.

1. By treating the generality of vegetable substances with ether the latter dissolves fat and wax readily and completely; alcohol dissolves these bodies also, but less readily, and only at the boiling heat, and as it deposits them again on cooling, and as filtering is retarded thereby, it becomes necessary to employ ether for removing the rest of fat or wax. These two substances, therefore, are passing into two different solvents. If the analysis is commenced with alcohol, this inconvenience increases when, as in seeds, the quantity of fat or wax predominates, and it can only be avoided by the previous treatment with ether.

2. Certain alkaloïds, bitter substances or resins, dissolve in alcohol and in ether, others only in alcohol. Now, by commencing

the analysis with alcohol the whole of them is dissolved, while by commencing with ether a separation of two different groups is effected at the outset.

3. Not less advantageous is the previous treatment with ether and then with alcohol for the subsequent one with water, whereas, if the commencement be made with water, inconveniences of various kinds are incurred. Amongst these stand out in the first line the difficulty of filtering, caused sometimes, it is true, by a considerable amount of gum, but also and often alone by finely suspended particles of resins and fats. These could, indeed, easily be removed by a few drops of dissolved acetate of lead, but this would disturb the course of the analysis by introducing acetic acid and by otherwise complicating the process. Since the water is to be employed not only cold but also hot, fats and resins present would be liable to undergo alterations, and greater still would be the difficulty with amylaceous substances, since the formation of a paste would make straining impossible, and to overcome this difficulty by means of adding an acid, in order to convert the paste of starch into sugar, would involve troubles of another kind, for instance, the breaking up of glucosids or resins, or the displacement of volatile acids.

Before commencing the analysis the question must be answered, how much of the material has to be worked upon, and how much may be available. If it consists of whole herbs or of parts of these as roots, barks, leaves, flowers or seeds, no more than 100 grammes of the substance should be employed, even if there be no scarcity of material. With very costly or not easily procurable substances a less amount must suffice, and with gummous or resinous exudations or with excretions of other kind it is possible to operate even upon 20 grammes, since the number of constituents of these bodies is comparatively small.

After the analysis, completed according to I. to VII., has given a clear idea of the chemical constitution of the substance under investigation, then those constituents which have been obtained in too small a quantity for a thorough investigation, such as alkaloïds, bitter substances, volatile oils, volatile acids, must be prepared from considerably larger quantities of the raw material, according to the methods indicated under VIII. to X.

I. QUANTITATIVE ESTIMATION OF THE WATER.

Weigh off from the substance in the possibly finest state of comminution 2 to 5 grammes, according to its bulk, into a platinum crucible, the weight of which and of its lid having been before carefully determined; place the crucible uncovered into a metallic air-bath furnished with a centigrade thermometer, put the whole

on a little clay-stove, and heat by means of a very small gas-flame or of a spirit-lamp to 120°, and keep at this temperature for about an hour. After a few trials the operator will soon become accustomed to control the temperature at nearly 120°, by placing the flame at the requisite distance from the air-bath; and by using for drying operations of this kind the same stove, the same lamp, and the same length of flame, no new trials for regulating the degree of heat will be required afterwards. A difference of a few degrees above or below 120° is of no consequence; but the mercury should never fall below 115° nor rise above 125°. After the substance has been thus heated for an hour, remove the flame, cover the crucible with the lid, shut the air-bath, take out the crucible when quite cold, place on a balance and determine the loss of weight.

Afterwards the same process of heating and weighing is once more to be repeated; if the second result agrees exactly with the first, or if it only differs by a few milligrammes, no third trial is required; else the heating process has to be repeated a third time or more, until with two following operations the same result be obtained.

Lastly the loss of weight is calculated for 100 parts, and the result is registered as the amount of percentage of water of the substance.

II. TREATMENT WITH ETHER.

Place 10 grammes (or less, see above) of the air-dried and possibly fine reduced substance into a glass flask of to litres capacity; add of ether of 0.720 until after thoroughly soaking the substance is covered or 1 inch high by the liquid, secure the flask with a cork and shake occasionally, taking care lest portions of the contents should get into the neck of the vessel. Having left it to macerate for four days, lift the cork a little, warm the flask in a water-bath or in any other manner to a temperature below the boiling-heat of ether (36°) for a few hours, remove the mattrass, and again macerate for two days.

Now transfer the contents of the flask (should the ether contain a great quantity of oil, resin, &c., pour out first the liquid so far as it easily can be removed, and after it has passed the filter, add the remaining substance with the aid of small quantities of fresh ether), into a displacement apparatus, rinse the flask repeatedly with ether, and wash the substance with this and with small quantities of ether until the latter assumes not only no colour, but leaves, on evaporating a few drops on a watch-glass, no residue of any consequence.

To push the washing to this degree, requires mostly much ether and also time, but it is necessary in order to prevent (1) that any portions of the constituents, soluble in ether, should be lost;

(2) that any portions of the constituents, soluble in alcohol and in ether, should be transferred to the alcoholic solution. The loss of time involved by performing this first part of the operation will be balanced by the simplification of the analysis, and as to the ether, it may easily be recovered by distillation.

Throw the substance, exhausted by ether, into a wide porcelain dish, spread out thinly, expose to the open air, stir assiduously with a porcelain spatula, drive off the rest of ether at a very gentle heat, keep at ordinary temperature for another day, weigh the whole, mix uniformly, estimate with 2 to 5 grammes of the substance, by drying at 120°, the amount of hygroscopic water, and calculate from this in centesimal proportions the weight of the whole substance in the anhydrous state. By adding to this weight the amount of water, found under I., and by deducting the sum from 100, the rest will be equal to the weight of the substances dissolved by ether. If, for instance, the amount of water under I. be 10%, and that of the substance exhausted by ether and in the anhydrous state 78%, then the ether will have dissolved 12%, because 100 - 10–78—12.

The ether of the united tinctures-the colour, taste, and reaction of which have preliminarily to be ascertained—is either distilled off, if it amounts to at least litre, or it is left to evaporate in an airy place, and lastly, with aid of a very gentle heat, in a glass beaker of known weight; and the residue is tested as below.

For recovering the ether choose a tubulated retort, which would hold at least double the quantity, or fill to one-half and add successively of the ether to keep at the same level. The tubulus of this retort must be as wide as possible, and fixed in such a way as to allow the contents to be poured out to the last drop. After filling the retort with the ethereous solution, plunge into the liquid a glass rod, of such a length as to protrude about one inch out of the liquid, place the retort in a water bath, adapt to it a Goebel's refrigerator and distil at least of its contents. Pour what is left in the retort into a glass beaker (weighed), rinse the retort with small portions of the distillate, and keep the beaker with the liquid and a glass rod in it in a moderately warm place. After the ether has nearly evaporated, add to the remnant 10 grammes of distilled water, warm until the ethereous smell has completely disappeared, and let cool.

The contents of the beaker, now, will consist either of two different strata of liquids, A and B, and of a more or less solid, tough, plastic mass, C, or of the latter and only one kind of liquid. In the first case, the upper liquid A is a fat, this, for instance, in analysis of seeds largely present; has only one liquid been obtained, then remains all that is said under A as a matter of course unnoticed.