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Fig. 87.

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 onlyth of a grain of phosphorus, and accordingly only 1 part of phosphorus in 100,000 parts of mixture, you may distil over 3 oz. of it-which will take at least half-an-hourwithout 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

* [Instead of this vertical condenser, the apparatus shown in Fig. 4 may be Lsed.]

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 319 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 medico-legal 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.

The experiment should be made in a perfectly dark room, best at night. If it is made in the daytime the room should be darkened by aid of curtains or blinds, so that no reflections whatever from the surfaces of the glass vessels or of the liquids moving in them shall occasion mistakes. It is advisable, even, especially when very minute traces of phosphorus are searched for, to pass the evolution-tube through a screen, at b, to prevent such reflections being occasioned by the light of the lamp by which the flask is heated.

The residue of the distillation is further examined according to (324) for phosphorous acid. The distillate, also, may be tested in the same manner to confirm the presence of phosphorus, or of phosphorous acid arising from its oxidation. 4. Another sample of the substance may be examined, 320 according to experiments made by Neubauer and myself* in the following manner. It is brought into a flask with doublyperforated stopper, water is added, if necessary, and dilute sulphuric acid to acid reaction. Washed carbonic acid gast is now slowly conducted through the mixture by means of a glass tube passing through the cork and reaching nearly down to the bottom of the flask. From a short tube above, the current of gas is led through one or two V-formed tubes which contain neutral solution of nitrate of silver. When he flask is filled with carbonic acid it is warmed in a waterbath. The experiment is kept up for several hours. If free phosphorus be present, a portion of it volatilizes unoxidized in the stream of carbonic acid, and on passing into the silversolution, produces there an insoluble black precipitate of * Zeitschrift f Analyt. Chem., 1, 336.

The apparatus, Fig. 35 (300), may be conveniently employed.

phosphide of silver, together with phosphoric acid. Since a black insoluble precipitate may be caused by various volatile reducing agents or by hydrosulphuric acid, its appearance is not proof of the presence of phosphorus, though its non-formation demonstrates conclusively that free phosphorus is absent. A PRECIPITATE formed in the silver solution in the above 321 experiment is collected on a filter (which has been previously washed with dilute nitric acid and water), and is well washed with water. The phosphide of silver, which may be contained in this precipitate, is detected by the method of Blondlot, improved by Dussard.* a Fig. 38. is an apparatus for evolving hydrogen; b is filled with fragments of pumice-stone drenched with concentrated potassa-lye; c is a common spring clamp; da clamp that can be nicely adjusted by means of a screw or wedge; e is a platinum jet which is kept cool by means of moistened cotton. This platinum jet is essential, since the flame would be colored yellow if burned directly from a glass tube.

At the outset it is needful to test the sulphuric acid and zine to demonstrate that they yield hydrogen free from phosphuretted hyd ogen. For this purpose allow the gas to evolve until air is displaced from the apparatus, then close c until the acid has been forced into f, then closed, open c, and lastly open d, cautiously inflaming the gas at the jet and properly regulating its issue. If the flame, when examined. in a rather dark place, is colorless, exhibits no trace of a green cone in its interior and no emerald-green tinge when a * Zeitschrift f. Analyt. Chem. 1. 129.

porcelain dish is depressed into it, the hydrogen is pure. After verifying this result by a second trial, the precipitate to be examined is rinsed into f, care being taken that it passes completely into a, and the flame is again observed as before. In case but a minimum of phosphide of silver be present the green inner cone and emerald-green coloration of the flame will be perceptible.

The SOLUTION filtered from the silver precipitate, is freed 322 from excess of silver by hydrochloric acid, filtered through a well purified filter, strongly concentrated in a porcelain capsule, and finally tested for phosphoric acid by means of molybdate of ammonia or magnesia mixture.

In this manner we have most plainly detected the phosphorus of a common match mixed with a large quantity of putrefied blood, and in presence of those substances which prevent luminosity in the method of Mitscherlich.

5. When enough phosphorus is present to weigh, its esti- 323 mation is practicable by adopting Scherer's modification of the process of Mitscherlich. The mass, acidified with sulphuric acid, is distilled in an atmosphere of carbonic acid gas. For this purpose it is best to fit into the cork of the flask in which the mixture is distilled, a second tube through which pure carbonic acid may be transmitted into the distilling apparatus, until it is completely filled, when the stream of gas may be cut off and the process continued as usual. The receiver may consist of a flask with a doubly perforated cork, one opening of which passes over the end of the condensing tube, the other carrying a bent glass tube which is connected with a U tube containing solution of nitrate of silver.

The

When the distillation is finished, globules of phosphorus are found in the receiver, which, after again establishing a gentle stream of carbonic acid, are united by gently heating and then are washed and weighed as described (319). solution poured off from the globules is luminous in the dark, when shaken, though not to the same degree as in Mitscherlich's process. The phosphorus in this liquid may be determined, after oxidation, by nitric acid or chlorine, as phosphoric acid; though, only, when the operator is certain that none of the contents of the distilling flask, which usually contain phosphoric acid, have spirted into the condenser. The entire quantity of phosphorus is obtained by adding to that, thus determined, what exists in the U tube. Its contents are treated with nitric acid, the silver thrown down by hydrochloric acid, filtered through a washed filter, concentrated, precipitated as phosphate of ammonia-magnesia, and weighed as phosphate of magnesia.

B. Detection of Phosphorous Acid.

In case free phosphorus itself has not been detected by the 324 above methods, it is needful to look for the first product of its oxidation, viz. phosphorous acid. To this end the residue of the distillation (318) or (323), or also the residue of (320) is brought into the apparatus, Fig. 38, and tested as described (321), as to any green coloration of the evolved hydrogen. If the phosphorous reaction appears it is sufficient; otherwise, organic matters may have hindered its production. If, therefore, the flame is not colored, the clamp is closed and a U tube containing neutral solution of nitrate of silver is affixed to the apparatus and the gas is allowed to stream slowly through the silver solution for many hours. In presence of phosphorous acid, phosphide of silver is formed, which is filtered off and examined as directed in (321).

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

§ 231.

A. PREPARATION OF THE Аsh.

It is sufficient for the purposes of a qualitative analysis to 325 incinerate 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, over which a wide glass tube (lamp chimney) is supported to increase the access of air. 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, 4th Edition, § 250.

B. EXAMINATION OF THE ASH.

As the qualitative analysis of the ash of a vegetable sub- 320 stance 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 present, or also with a view to make, as far as prac