E. Mitscherlich, who has published the latest treatise on the 316 subject, recommends the following method as the simplest and best:†

Mix the substance under examination with water and some sulphuric acid, and subject the mixture to distillation in a flask, A (see Fig. 31). This flask is connected with an evolution tube, b, and

the latter again with a glass cooling or condensing tube, c c c, which passes through a perforated cork a, in the bottom of a cylinder, B, into a glass vessel, C. Cold water runs from D, through a stopcock, into a funnel, i, which extends to the bottom of B; the warmed water flows off through g.

Now, if the substance in A contains phosphorus, there will appear, in the dark, in the upper part of the condensing tube at the point r, where the aqueous vapors distilling over enter that part of the tube, a strong luminosity, usually a luminous ring. If you take for distillation 5 oz. of a mixture containing only th of a grain of phosphorus, and accordingly only 1 part of

"Journal für prakt. Chemie," vol. 66, p. 238.

+ I have tried this method, and found it to answer perfectly.

phosphorus in 100,000 parts of mixture, you may distil over 3 oz. of it-which will take at least half-an-hour-without the luminosity ceasing; Mitscherlich, in one of his experiments, stopped the distillation after half-an-hour, allowed the flask to stand uncorked a fortnight, and then recommenced the distillation: the luminosity was as strong as at first. If the fluid contains substances which prevent the luminosity of phosphorus in general, such as ether, alcohol, or oil of turpentine, no luminosity is observed so long as these substances continue to distil over. In the case of ether and alcohol, however, this is soon effected, and the luminosity accordingly very speedily makes its appearance; but it is different with oil of turpentine, which exercises a lasting preventive influence upon the manifestation of this reaction.

After the termination of the process, globules of phosphorus 317 are found at the bottom of the receiver, C. Mitscherlich obtained from 5 oz. of a mixture containing grain of phosphorus, so many globules of that body that the one-tenth part of them would have been amply sufficient to demonstrate its presence. In medicolegal investigations these globules should first be washed with alcohol, and then weighed. A portion may afterwards be subjected to a confirmatory examination, to make quite sure that they really consist of phosphorus: the remainder, together with a portion of the fluid which shows the luminosity upon distillation, should be sent in with the report.

3. Examination of the Inorganic Constituents of Plants, Animals, or Parts of the same, of Manures, &c. (Analysis of Ashes.)

$226.

A. PREPARATION OF THE ASH.

It is sufficient for the purposes of a qualitative analysis to in- 318 cinerate a comparatively small quantity of the substance which it is intended to examine for its inorganic constituents; the substance must previously be most carefully cleaned. The incineration is effected best in a small clay muffle, but it may be conducted also in a Hessian crucible placed in a slanting position, or, under certain circumstances, even in a small porcelain or platinum dish. The heat must always be moderate, to guard against the volatilization of certain constituents, more especially of metallic chlorides. It is not always necessary to continue the combustion until all the carbon is consumed. With ashes containing a large proportion of fusible salts, as, e. g. the ash of beetroot molasses, it is even advisable to effect, in the first place, complete carbonization, then to boil the charred mass with water, and finally to incinerate the washed and dried residue. For further particulars see Quantitative Analysis, 3rd Edition, § 250.

B. EXAMINATION OF THE ASH.

As the qualitative analysis of the ash of a vegetable substance 319 is usually undertaken, either as a practical exercise, or for the purpose of determining its general character, and the state or condition in which any given constituent may happen to be pre

sent, or also with a view to make, as far as practicable, an approximate estimation of the respective quantities of the several constituents, it is usually the best way to examine separately; (1) the part soluble in water; (2) the part soluble in hydrochloric acid; and (3) the residue which is insoluble in either menstruum. This can be done the more readily, as the number of bodies to which regard must be had in the analysis is only small, and the several processes may accordingly be expeditiously performed.

a. Examination of the Part soluble in Water.

Boil the ash with water, filter, and whilst the residue is being washed, examine the solution as follows:

1. Add to a portion, after heating it, hydrochloric acid in excess, 320 warm, and let the fluid stand at rest. Effervescence indicates CARBONIC ACID, combined with alkalies; odor of hydrosulphuric acid indicates the SULPHIDE of an ALKALI METAL, formed from an alkaline sulphate by the reducing action of the carbon. Turbidity from separation of sulphur, with odor of sulphurous acid, denotes a HYPOSULPHITE (which occurs occasionally in the ash of coal). Filter, if necessary, and add to the filtrate or to the fluid if no filtration is required-some chloride of barium; the formation of a white precipitate indicates the presence of SULPHURIC ACID.

2. Evaporate another portion of the solution until it is reduced 321 to a small volume, add hydrochloric acid to acid reaction-effervescence indicates the presence of CARBONIC ACID-evaporate now to dryness, and treat the residue with hydrochloric acid and water. The portion left undissolved consists of SILICIC ACID. Filter, add ammonia, chloride of ammonium, and sulphate of magnesia; the formation of a white precipitate indicates the presence of PHOSPHORIC ACID. Instead of this reaction, you may also mix the fluid filtered from the silicic acid with acetate of soda, and then cautiously add, drop. by drop, sesquichloride of iron, or you may test with molybdate of ammonia (§ 143).

3. Add to another portion of the solution nitrate of silver as 322 long as a precipitate continues to form; warm" gently, and then cautiously add ammonia; if a black residue is left, this consists of sulphide of silver, proceeding from the sulphide of an alkali metal, or from a hyposulphite. Mix the ammoniacal solution now-after previous filtration if necessary-cautiously with nitric acid until it is exactly neutralized. If this produces a bright yellow precipitate, the phosphoric acid found in 2 was present in the tribasic, if a white precipitate, it was present in the bibasic form. Add more

nitric acid. This effects the solution of the phosphate of silver precipitate. But if CHLORINE (iodine,* bromine) is present, a portion of the precipitate remains undissolved, or the fluid appears turbid.

4. Acidify a portion of the solution with hydrochloric acid, and 323 then make it alkaline with ammonia; mix the alkaline fluid with oxalate of ammonia, and let it stand at rest. The formation of a

*To detect the iodine in aquatic plants, dip the plant in a weak solution of potassa (Chatin), dry, incinerate, treat with water, and examine the aqueous solution as directed § 211, 2, c, ẞ, aa (258).

white precipitate indicates LIME. Filter, and mix the filtrate with ammonia and phosphate of soda; the formation of a crystalline precipitate, which often becomes visible only after long standing, indicates MAGNESIA. Magnesia is often found in distinctly appreciable, lime only in exceedingly minute, quantity, even when alkaline carbonates and phosphates are present.

5. For POTASSA and SODA examine as directed § 195.

b. Examination of the Part soluble in Hydrochloric Acid.

Warm the residue left undissolved by water with hydrochloric 324 acid*―effervescence indicates CARBONIC ACID, combined with alkaline earths; evolution of chlorine denotes oXIDES OF MANGANESEevaporate to dryness, and heat a little more strongly, to effect the separation of the silicic acid; moisten the residue with hydrochloric acid and some nitric acid, add water, warm, and filter.

1. Test with hydrosulphuric acid. If this produces any other than a perfectly white precipitate, you must examine it in the usual way. The ashes of plants occasionally contain COPPER; if the plant has been manured with excrements deodorized by nitrate of lead, they may contain LEAD; other metals are also occasionally found.

2. Mix a portion of the original solution with carbonate of soda, 325 as long as the precipitate formed redissolves upon stirring; then add acetate of soda, and some acetic acid. This produces, in most cases, a white precipitate of PHOSPHATE OF SESQUIOXIDE OF IRON. If the fluid in which this precipitate is suspended is reddish, there is more sesquioxide of iron present than corresponds to the phosphoric acid; if it is colorless, add sesquichloride of iron, drop by drop, until the fluid looks reddish. (From the quantity of the precipitate of phosphate of sesquioxide of iron formed you may estimate the PHOSPHORIC ACID present.) Heat to boiling,t filter hot, and mix the filtrate, after addition of ammonia, with yellowish sulphide of ammonium, in a stoppered flask; should a precipitate form, after long standing, examine this before the blowpipe for MANGANESE, and the fluid filtered from it for LIME and MAGNESIA, in the usual way (§ 226, B, a, 4 [323]).

c. Examination of the Residue insoluble in Hydrochloric Acid.

The residue insoluble in hydrochloric acid contains,

1. The silicic acid, which has separated on treating with hydro- 326 chloric acid.

2. Those ingredients of the ash which are insoluble in hydrochloric acid. These are, in most ashes, sand, clay, carbon; substances, therefore, which are present in consequence of defective cleaning or imperfect combustion of the plants, or matter derived from the crucible. It is only the ashes of the stems of cereals and others abounding in silicic acid, that are not completely decomposed by hydrochloric acid.

* If the residue still contains much carbon, after further incineration.
+ If this should fail to decolorize the fluid, add some more acetate of soda.

Boil the washed residue with solution of carbonate of soda in 327 excess, filter hot, wash with boiling water, and test for silicic acid in the filtrate by evaporation with hydrochloric acid. If the ash was of a kind to be completely decomposed by hydrochloric acid, the analysis may be considered as finished-for the accidental admixture of clay and sand will rarely interest the analyst sufficiently to warrant a more minute examination by fluxing. But, if the ash abounded in silicic acid, and it may therefore be supposed that the hydrochloric acid has failed to effect complete decomposition, evaporate half of the residue insoluble in solution of carbonate of soda, with pure solution of soda in excess, in a silver or platinum dish, to dryness. This decomposes the silicates of the ash, whilst but little affecting the sand. Acidify now with hydrochloric acid, evaporate to dryness, &c., and proceed as in b (324). For the detection of the alkalies use the other half of the residue. Compare § 205, 2 (228).

SECTION III.

EXPLANATORY NOTES AND ADDITIONS TO THE SYSTEMATIC COURSE OF ANALYSIS.

I. ADDITIONAL REMARKS TO THE PRELIMINARY EXAMINATION.

To §§ 173-176.

THE inspection of the physical properties of a body may, as already stated § 173, in many cases enable the analyst to draw certain general inferences as to its nature. Thus, for instance, if the analyst has a white substance before him, he may at once conclude that it is not cinnabar, or if a light substance, that it is not a compound of lead, &c.

Inferences of this kind are quite admissible to a certain extent; but if carried too far, they are apt to mislead the operator, by blinding him to every reaction not exactly in accordance with his preconceived notions.

As regards the examination of substances at a high temperature, platinum foil or small iron spoons may also be used in the process; however, the experiment in the glass tube gives, in most cases, results more clearly evident, and affords, moreover, the advantage that volatile bodies are less likely to escape detection, and that a more correct and precise notion can be formed of the nature of the heated substance, than exposure on platinum foil or in an iron spoon will permit. In the case of minerals it is always advisable to extend the examination in the dry way, also to fluorine (§ 147, 8). To ascertain the products of oxidation of a body, it is sometimes advisable also to heat it in a short glass-tube, open at both ends, and held in a slanting position; small quantities of a metallic sulphide, for instance, may be readily detected by this means. (Compare 156, 6.)

With respect to the preliminary examination by means of the blow