where it is required to separate that acid from articles of food or from the contents of the stomach, and thus to prove its presence, it is highly necessary to act with the greatest expedition, as the hydrocyanic acid speedily undergoes decomposition. Still this decomposition is not quite so rapid as is generally supposed, and indeed it requires some time before the complete decomposition of the whole of the acid present is effected.*

Although hydrocyanic acid betrays its presence, even in minute quantities, by its peculiar odor, still this sign must never be looked upon as conclusive. On the contrary, to adduce positive proof of the presence of the acid, it is always indispensable to separate it, and to convert it into certain known compounds.

The method of accomplishing this is based upon distillation of the acidified mass, and examination of the distillate for hydrocyanic acid. Now, as the non-poisonous salts, ferro- and ferricyanide of potassium, on distillation, likewise yield a distillate containing hydrocyanic acid, it is, of course, indispensable-as Otto very properly observes-first to ascertain whether one of these salts may not be present. For this purpose, stir a small portion of the mass to be examined with water, filter, acidify the filtrate with hydrochloric acid, and test a sample of it with sesquichloride of iron, another with sulphate of protoxide of iron. If no blue precipitate forms in either, soluble ferro- and ferricyanides are not present, and you may safely proceed as follows:

Test, in the first place, the reaction of the mass under examina- 310 tion; if necessary, after mixing and stirring it with water. If it is not already strongly acid, add solution of tartaric acid until the fluid strongly reddens litmus paper; introduce the mixture into a retort, and place the body of the retort, with the neck pointing upwards, in an iron or copper vessel, but so that it does not touch the bottom, which should, moreover, by way of precaution, be covered with a cloth; fill the vessel with a solution of chloride of calcium, and apply heat, so as to cause gentle ebullition of the contents of the retort Conduct the vapors passing over, with the aid of a tight-fitting tube, bent at a very obtuse angle, through a Liebig's condensing apparatus, and receive the distillate in a small, weighed flask. When about half-an-ounce of distillate has passed over, remove the receiver, and replace it by a somewhat larger flask, also previously tared. Weigh the contents of the first receiver, and proceed as follows:

a. Mix one-fourth of the distillate with solution of potassa 311 or soda to strongly alkaline reaction, and then add a small quantity of solution of sulphate of protoxide of iron, mixed with a little sesquichloride of iron.

b. Treat another fourth as directed § 155, 7, to convert the 312 hydrocyanic acid into sulphocyanide of iron. As the distillate might, however, contain acetic acid, do not neglect to add some

*Thus I succeeded in separating a notable quantity of hydrocyanic acid from the stomach of a man who had poisoned himself with that acid in very hot weather, and whose intestines were handed to me full 36 hours after death.-A dog was poisoned with hydrocyanic acid, and the contents of the stomach, mixed with the blood, were left for 24 hours exposed to an intense summer-heat, and then examined: the acid was still detected.

hydrochloric acid after the sesquichloride of iron, in order to neutralize the adverse influence of the acetate of ammonia. Compare $155, 7.

c. If the experiments a and b have demonstrated the pre- 313 sence of hydrocyanic acid, and you wish now also to approximately determine its quantity, continue the distillation, until the fluid passing over contains no longer the least trace of hydrocyanic acid; add one-half of the contents of the second receiver to the remaining half of the contents of the first, mix the fluid with nitrate of silver, then with ammonia until it predominates, and finally with nitric acid to strongly acid reaction. Allow the precipitate which forms to subside, filter on a tared filter, dried at 212° F., wash the precipitate, dry it thoroughly at 212° F., and weigh. Ignite the weighed precipitate in a small porcelain crucible, to destroy the cyanide of silver, fuse the residue with carbonate of soda and potassa—to effect the decomposition of the chloride of silver which it may contain-boil the mass with water, filter, acidify the filtrate with nitric acid, and precipitate with nitrate of silver; determine the weight of the chloride of silver which may precipitate, and deduct the amount found from the total weight of the chloride and cyanide of silver: the difference gives the quantity of the latter; by multiplying the quantity found of the cyanide of silver by 0-2017, you find the corresponding amount of anhydrous hydrocyanic acid; and by multiplying this again by 2-as only one-half of the distillate has been used-you find the total quantity of hydrocyanic acid which was present in the examined mass.

Instead of pursuing this indirect method, you may also deter- 314 mine the quantity of the hydrocyanic acid by the following direct method: Introduce half of the distillate into a retort, together with powdered borax; distil to a small residue, and determine the hydrocyanic acid in the distillate as cyanide of silver. Hydrochloric acid can no longer be present in this distillate, as the soda of the borax retains it in the retort (Wackenroder).

III. METHOD FOR THE DETECTION OF PHOSPHORUS.

$ 225.

Since phosphorus paste has been employed to poison mice, &c., 315 and the poisonous action of lucifer matches has become more extensively known, phosphorus has not unfrequently been resorted to as an agent for committing murder. The chemist is therefore occasionally called upon to examine some article of food, or the contents of a stomach, for this substance. It is obvious that, in cases of the kind, his whole attention must be directed to the separation of the phosphorus in the free state, or to producing such reactions as will enable him to infer the presence of free phosphorus; since the mere finding of phosphorus in form of phosphates would prove nothing, as phosphates invariably form constituents of animal and vegetable bodies.

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 4th 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).