Chapter IV: Appendix: 163 (2)

This apparatus consists of a stand _S_, (Fig. 9) supporting a balloon _A_, which serves as the reservoir of the suspected solution, and a funnel _B_, into which the neck of the balloon is dipped. The funnel _B_ is bent at a right angle and is drawn out at its lower end under which the dish _C_ is placed for the reception of the escaping fluids. A fine wire of pure gold, forming the negative electrode of a Bunsen's battery, passes through the lower extremity of the funnel. The end of this wire nearly comes in contact with a second wire, inserted in the upper part of the funnel, and connected with the positive pole of the battery. If the balloon filled with the solution is inverted and immersed in the funnel _B_, its neck will be submerged at first; soon, however, it becomes uncovered, owing to the depression of the level of the fluid caused by the escape of the latter through the tapering extremity of the funnel: a bubble of air then passes in the balloon and expels a drop of the solution. This process is repeated at short intervals, causing a continuous flow of the fluid, the rapidity of which is easily regulated by elevating or lowering the balloon, thus raising or depressing the level of the liquid. The apparatus having been mounted in this manner and the battery set in action, the disengagement of gas commences. Should mercury be contained in the solution under examination, this metal will be deposited upon the negative wire. When the operation is completed this wire is detached from the apparatus, washed with ether, and dried. It is then introduced into a small tube provided with a bulb, and the mercury volatilized by means of the blow pipe flame: the metal condenses in the bulb of the tube in globules which are readily recognized. They can also be dissolved in nitric acid, and the presence of a mercurial salt in the solution confirmed by further tests.

The solution to be examined in the preceding apparatus, is prepared as follows:

The suspected organic matter is treated with cold sulphuric acid of 66° _B._ until liquefied, and hypochlorite of lime, and distilled water then added: if necessary, the evolution of chlorine can be accelerated by a further addition of sulphuric acid. As soon as the liquid becomes clear, it is filtered, concentrated and examined as described above. The solution contains the mercury in the state of bichloride, a salt soluble in water and well adapted to the above test.

The substitution of a large balloon, having a capacity of about 2 litres, in place of the small vessel of Flandin and Danger's apparatus, is to be recommended as doing away with the necessity of evaporation; an operation which invariably causes a loss of substance. The apparatus, modified in this manner, is the most delicate in use for the detection of mercury.

DETECTION OF PHOSPHORUS.

ORFILA'S METHOD.

The solid substances found in the alimentary canal are mechanically separated from the fluids present by means of a linen cloth. They are then examined by aid of a magnifying glass, and any fragments of phosphorus found separated and preserved under water. If none are discovered, the presence of phosphorescent vapors may possibly be detected by examining the materials in the dark. In any case, a portion of the suspected materials should be treated with nitrate of silver: in presence of phosphorus the materials acquire, first, a reddish-brown, then, a black color. The remaining portion is spread upon a shovel and heated: a white flame, burning at various points of the mass, and originating from the combustion of phosphorus, is observed, if this body be contained in the substances under examination. This method is evidently far from perfect.

MITSCHERLICH'S METHOD.

Mistcherlich's method is based upon the luminosity of the vapors of phosphorus. The suspected materials are moistened with dilute sulphuric acid, and heated, in a flask communicating with a glass worm which passes through a glass cooler into a receiver. If the apparatus is placed in the dark, and the materials contain phosphorus, luminous vapors will be observed in the flask and receiver. When the quantity of the poison present is considerable, the phosphorous acid formed can be collected and its properties tested.

DUSART'S METHOD, AS MODIFIED BY BLONDLOT.

Dusart's process takes advantage of the facility with which hydrogen combines with phosphorus. The substances under examination are placed between two asbestus stoppers in a tube, one end of which tapers to a point, and a current of pure hydrogen conducted over them. In presence of phosphorus the evolved gas will burn with a green flame, and, upon bringing this in contact with a porcelain plate, red spots will be deposited upon the latter. _Blondlot_ prefers to introduce the suspected materials into the flask in which the hydrogen is generated. He employs the apparatus represented in Fig. 10: _a_ is a flask for evolving hydrogen; _b_ is a U tube, filled with fragments of pumice stone which are saturated with a concentrated solution of potassa; _c_ is a Mohr clamp; _d_ a screw-clamp; _e_ a platinum jet. This jet is necessary in order to avoid a yellow coloration of the flame by the soda contained in the glass. Pure hydrogen is at first evolved, in order to ascertain that the flame is colorless and red spots are not produced when it is intersected by a cold plate. The purity of the reagents used having thus been confirmed, the clamp _d_ is closed until the acid is forced back into _f_; and the materials to be examined are then added to the fluid. Upon opening the clamp the liquid passes from _f_ into _a_, and the evolution of gas recommences. The gas is then ignited: the flame possesses the characteristic properties mentioned above, if the suspected substances contain phosphorus.

METHOD PROPOSED BY FRESENIUS AND NEUBAUER.

According to this method, the materials are brought into a flask provided with a doubly-perforated stopper, and water, acidulated with sulphuric acid, added. The flask is then heated over a water-bath, and a current of carbonic acid conducted through the mixture for at least two hours. The gas, on leaving the flask, passes into a solution of nitrate of silver. Should no precipitate form in this solution, the absence of free phosphorus is established, for, were this body present, a portion would be volatilized, and a black precipitate, consisting of phosphide of silver, together with phosphoric acid, produced. The formation of a black precipitate is, however, not necessarily a proof of the presence of phosphorus. In order to conclusively determine the character of the precipitate, it is collected on a filter and examined by the method of Dusart and Blondlot.

This process has given result in cases where none were obtained by Mistcherlich's method. It possesses, moreover, an advantage over the latter process, in not being influenced by the presence of foreign bodies; whereas, in Mistcherlich's method, some time must elapse before the luminosity of the vapors becomes apparent if ether or alcohol is contained in the solutions, and this phenomenon totally fails to appear in presence of oil of turpentine.

DETECTION OF PHOSPHORUS BY THE USE OF BISULPHIDE OF CARBON.

In a report read before the Academy of Sciences in 1856, presented by an examining commission, of which MM. _Dumas_, _Pelouze_ and _Claude Bernard_ were the reporters, the following results were contained: Phosphorus may remain, in the _free state_, in the organs fifteen days after death, and even then its isolation can easily be accomplished. For this purpose the stomach or intestines, and the articles of food contained therein, are cut into pieces and treated with bisulphide of carbon. Upon filtering the liquid, a solution is obtained containing all the phosphorus present, which exhibits the following properties: 1st, When ignited, it burns with a very luminous flame; 2nd, if allowed to spontaneously evaporate (the combustion of the phosphorus being prevented by the organic matter present [_Naquet_]) an inflammable residue is obtained, which, if dissolved in boiling monohydrated nitric acid, gives a solution that, after saturation with ammonia, produces a precipitate soluble in acids in solutions of barium salts. If the solution is mixed with perchloride of iron, and the sesquioxide of this metal subsequently eliminated by the addition of ammonia, it no longer causes a precipitation in barium solutions. The fluid acquires a yellow coloration when boiled with a solution of molybdate of ammonia.

According to our personal experience, the apparatus employed by Flandin and Danger for the detection of arsenic, can also be made use of in the examination of the bisulphide of carbon solution. To this end, the fluid supposed to contain phosphorus is mixed with perfectly pure alcohol, and the mixture placed in a small spirit-lamp provided with a very loose asbestus wick. The lamp is then ignited and the flame introduced in the combustion tube _D_ (Fig. 11).

By the combustion of the mixture, sulphurous, carbonic, phosphorous acids and water are formed. The water condenses in _c_, and, falling into the dish _F_, carries with it the sulphurous and phosphorous acids. The acid liquid collected in this way is evaporated to dryness, some nitric acid added, and the solution again evaporated. The remaining mass is then dissolved in water to which some ammonia is added, and the solution tested for phosphoric acid. This method is an advantageous one as the phosphoric acid formed must originate from phosphorus in the _free state_, and not from any phosphates which, owing to the presence of organic matter, might be contained in the bisulphide of carbon solution. It would, however, lead the analyst into error if the person, supposed to have been poisoned had eaten cerebral substances or eggs previous to death, as these contain glycero-phosphoric acid; it is therefore advisable to compare the results given by this process with those obtained by the use of other methods.

DETECTION OF PHOSPHOROUS ACID.

Provided free phosphorus has not been detected, it is necessary to search for phosphorous acid. To this end, the residue remaining in the flask, in either Mistcherlich's or Fresenius and Neubauer's method, is introduced into the apparatus of Dusard and Blondlot. If the phosphorus reaction appears, it is sufficient; otherwise, its production may have been hindered by the presence of organic matter. In case, therefore, the flame is colorless, the evolved gas is conducted into a neutral solution of nitrate of silver. If the materials contain phosphorous acid, a precipitate of phosphide of silver is formed which should be collected and washed. The precipitate, which is now free from organic matter, is then examined for phosphorous acid by means of the apparatus of Dusard and Blondlot.

ESTIMATION OF PHOSPHORUS.

The best process for determining quantitatively the amount of phosphorus present is the one recommended by Fresenius and Neubauer. The gaseous current is continued until a fresh nitrate of silver solution is no longer precipitated. The solution is filtered, the precipitate washed and then dissolved in nitric acid. The silver is next precipitated by addition of hydrochloric acid, the fluid again filtered, and the precipitate well washed. The washings are added to the filtrate, and the liquid concentrated in a porcelain capsule. A solution of sulphate of magnesia, containing ammonia, is next added to the fluid, and the phosphoric acid determined as pyrophosphate of magnesia: the precipitate formed, is washed, heated to redness, in order to convert it into the pyrophosphate, and then weighed.

DETECTION OF ACIDS.

The search for acids is to be instituted exclusively in the alimentary canal and its contents. Were acids contained in the other organs, their presence would be due to the blood in which they had previously been absorbed, and, as in this case they would be partially neutralized by the bases contained in the blood, a conclusive decision in regard to their original existence in the suspected materials would be impossible, the salts of the acids usually searched for being normal constituents of the blood. In order to detect the presence of acids, the alimentary canal and contents are first boiled with water which is renewed until the solution ceases to exhibit an acid reaction when tested with litmus paper. The fluid is then filtered, alcohol added to the filtrate, in order to precipitate organic substances, the liquid again filtered, and the solution tested separately for the various acids as directed below.

HYDROCHLORIC ACID.

The solution is placed in a retort provided with a receiver and distilled until the residual fluid assumes a pasty consistence: the operation is then discontinued. If hydrochloric acid be present in the materials under examination, the distillate will have an acid reaction, and, upon addition of solution of nitrate of silver, a white precipitate, which is easily soluble in ammonia but insoluble in nitric acid and in short possesses all the properties of chloride of silver, will be formed.

NITRIC ACID.

The distillate, obtained as in the preceding process, is neutralized by the addition of potassa or soda, and evaporated to dryness. The residue is mixed with copper filings, and introduced into a glass tube closed at one end and provided at the other with a cork through which a delivery-tube passes. Sulphuric acid is then added to the mixture, the cork inserted, the tube heated, and the evolved vapors conducted into a solution of protosulphate of iron. The latter solution acquires a brown coloration which, upon addition of sulphuric acid, changes to a violet, if nitric acid be present. Upon conducting the disengaged gas into a solution of narcotine, the latter acquires a beautiful red color.

Another portion of the residue should deflagrate when saturated with an alkali and projected upon live coals.

SULPHURIC ACID.

In order to detect this acid, the solution obtained by treating the organs with water is not distilled but is concentrated to one-sixth of its original volume, and then agitated with ether for about ten minutes. By this treatment the ether takes up the free sulphuric acid, but not the acid sulphates present. After ten minutes contact, the ether is decanted and allowed to spontaneously evaporate. Upon treating the residue, which contains the free sulphuric acid and fatty substances, with water, a solution containing only the sulphuric acid is obtained. Nitrate of baryta is then added to a portion of the fluid: in presence of sulphuric acid, a white precipitate, insoluble in acids, is produced. If this is heated on charcoal before the blow-pipe, a mass is formed, which, when moistened with hydrochloric acid and placed upon a clean silver coin, produces a black spot on the metal. Another portion of the solution is mixed with copper and the mixture evaporated in a tube closed at one end: sulphurous acid is evolved towards the end of the operation. This gas is detected by allowing it to pass over paper saturated with a mixture of iodic acid and starch; a blue coloration is produced which, owing to the transformation of the iodine set free into hydriodic acid, subsequently disappears. (We have never been able to effect the disengagement of sulphurous acid spoken of above when an exceedingly dilute sulphuric acid was used, even upon evaporating the mixture to dryness, notwithstanding Orfila's statement that the reaction occurs very readily.)

PHOSPHORIC ACID.

The aqueous solution is evaporated to dryness, the residue taken up with alcohol of 44° B., the fluid again evaporated, and the second residue dissolved in water. Upon adding acetate of lead to the solution, a white precipitate is produced if phosphoric acid be present. The precipitate is washed, suspended in water and a current of sulphuretted hydrogen passed through the mixture. If the fluid is then filtered, and the excess of sulphuretted hydrogen expelled from the filtrate by boiling, a liquid possessing the distinctive properties of a solution of phosphoric acid will be obtained. This should then be submitted to the following tests: Some pulverized charcoal is added to a portion of the solution, the mixture evaporated to dryness, and the residue obtained introduced into a Hessian crucible heated to redness: in presence of a considerable amount of the acid, free phosphorous is liberated and burns with a bright flame in the upper part of the crucible. In case this reaction fails to occur, other portions of the fluid are treated with a solution of a baryta salt, which causes a white precipitate, soluble in nitric acid; with an ammoniated solution of sulphate of magnesia, which throws down a crystalline white precipitate; and by boiling with molybdate of ammonia, acidulated with nitric acid, which produces a yellow precipitation, or at least a yellow coloration of the solution.

OXALIC ACID.

The solution is subjected to the same treatment as in the search for phosphoric acid, with the exception that, instead of adding acetate of lead to the fluid obtained by taking up the residue left from the alcohol with water, it is divided into two portions which are examined separately. A solution of a lime salt is added to one portion: if oxalic acid be present, a precipitate, which is insoluble in acetic acid or in chloride of ammonium, and effervesces when slightly calcined and treated with hydrochloric acid, is formed. Nitrate of silver is added to the remaining portion of the solution: the formation of a precipitate, which detonates when dried and heated in a glass tube closed at one end, is further evidence of the presence of the acid.

ACETIC ACID.

The solution obtained by treating the alimentary canal with water is distilled, as in testing for nitric and hydrochloric acids, and the following properties verified in the distillate: 1st. It has an acid reaction, and possesses the odor of vinegar; 2nd, unless previously neutralized with a base, it fails to redden the per-salts of iron; 3rd, if the distillate is added to a solution of the per-salts mentioned and sulphuretted hydrogen conducted through the fluid, a black precipitate is formed; 4th, upon boiling the still acid fluid with a small quantity of starch, the property of the latter to become colored in presence of free iodine is not changed; 5th, if heated with an excess of litharge, a basic salt which restores the blue color to reddened litmus paper is produced.

HYDROCYANIC ACID.

The detection of hydrocyanic acid requires special precautions. The substances to be examined are mixed with water, if solids are present, and introduced into a retort provided with a delivery-tube which dips in a solution of nitrate of silver. The retort is then heated over a water-bath. If the evolved vapors produce a precipitate in the silver solution, the heating is continued until a fresh portion of the latter is no longer affected. The operation is now interrupted, hydrochloric acid added to the retort, and heat again applied. Should a second precipitation of cyanide of silver occur, the presence of a _cyanide_ in the suspected materials is indicated; whereas the formation of a precipitate by the simple action of heat would point to the presence of free hydrocyanic acid or cyanide of ammonium.[H] In case the latter compound is present, ammonia will be contained in the distillate.

[H] Ferrocyanides and ferricyanides--non-poisonous
compounds--likewise, evolve hydrocyanic acid when distilled with a
strong acid. Their presence is indicated by stirring a small portion
of the materials with water, filtering the fluid, acidulating the
filtrate with hydrochloric acid, and testing two portions: one with
sesquichloride of iron, the other with protosulphate of iron. If
either of the above salts be present, a blue precipitate is
produced.--_Trans._

In order to identify the cyanogen, a portion of the precipitate is collected upon a small filter, washed, dried, and then allowed to fall into a rather long tube, closed at one end, in the bottom of which some iodine has previously been placed. A column of carbonate of soda is then introduced above the precipitate for the purpose of retaining the excess of iodine probably taken. Upon heating the lower end of the tube, white fumes of iodide of cyanogen, which condense in needles upon the cold portion of the tube, are produced. These are easily recognized by aid of a magnifying glass. They are colorless and are readily volatilized by heat. Some ammonia is next added to a solution of protosulphate of iron, the precipitate formed thoroughly washed, and exposed to the air until it acquires a greenish hue. The iodide of cyanogen is then withdrawn from the tube and mixed with potassa-lye and the precipitate mentioned above. The mixture is evaporated to dryness, the residue obtained treated with water and the filtered solution then acidulated with hydrochloric acid. If a solution of a persalt of iron is now added to the fluid, a blue precipitate is formed. The addition of salts of copper produces a reddish precipitation.

The remainder of the precipitate formed in the nitrate of silver solution is heated with sulphur and then boiled with an aqueous solution of chloride of sodium: if cyanogen is contained in the precipitate, a solution of sulphocyanate of soda will be formed, and upon adding sesquichloride of iron an intense red coloration produced.

It is evident that the presence of another acid in the solution examined for hydrocyanic acid would render the detection of _cyanides_ impossible, but in all cases hydrocyanic acid can be separated without arriving at a decision in regard to its original state of combination. Nitric, hydrochloric, and several other acids would not be distilled at the temperature of the water-bath; an examination for these by the methods already described can therefore be instituted simultaneously with the search for hydrocyanic acid.

DETECTION OF ALKALIES AND ALKALINE EARTHS.

The separation of these bodies in the caustic state is a matter of difficulty owing to the great tendency they possess to become converted into carbonates; the carbonates of lime, baryta and strontia, moreover, being non-poisonous in their effects, will not be employed with criminal intent, and the carbonates of soda and potassa are extensively used as pharmaceutical preparations. Notwithstanding the small chances of success, the isolation of the compounds under consideration in the caustic state is to be attempted.

To this intent, the organs to be analysed, together with their contents, are placed in a glass retort provided with a receiver, water added, and the mixture boiled. The distillate will contain the ammonia present. When, however, putrefaction has begun, the detection of this compound does not necessarily indicate its original presence in the suspected materials. If, after an hour's boiling, the fluid in the retort possess an alkaline reaction, it is to be examined for soda, potassa, strontia, baryta and lime. The undistilled solution is filtered, the filtrate evaporated to dryness, and the residual mass treated with alcohol. By this treatment, potassa and soda go in solution, lime, baryta and strontia[I]--as well as the alkaline carbonates--remaining undissolved. The potassa and soda are separated from the other salts present by filtering and evaporating the alcoholic solution to dryness and then calcining the residue in a silver crucible. The mass, which should still be alkaline, is then dissolved in dilute sulphuric acid. If the solution is turbid, traces of baryta or strontia may still be present and should be removed by filtration. Some hydrochloric acid and solution of bichloride of platinum are then added to a portion of the filtered liquid: in presence of _potassa_ a yellow precipitate is formed.

[I] Baryta and strontia dissolve in alcohol, but only when they are
anhydrous and the alcohol is absolute, which is not the case here.

Another portion is treated with tartaric acid: a white granular precipitate is produced. Hydrofluosilicic acid is added to a third portion of the solution: the formation of a gelatinous precipitate is a further indication of the presence of potassa. If the preceding tests have given negative results, and a white precipitate is formed by the addition of antimonate of potassa to another portion of the solution, _soda_ is present. In both cases, it is necessary to confirm the results by means of the spectroscope.

The above reactions are distinctive only in the absence of metals precipitated by sulphuretted hydrogen, sulphide of ammonium or carbonate of soda, and small portions of the solution should be tested with these reagents.

In order to detect baryta, strontia and lime, the residue, insoluble in alcohol is dissolved in dilute nitric acid, and an excess of carbonate of ammonia added to the solution: the three bases, if present, are precipitated as carbonates. The precipitate formed is separated from the solution by filtration, dissolved on the filter in dilute hydrochloric acid, and the solution then filtered and divided into two parts: sulphuric acid is added to one, the fluid filtered from the precipitate of sulphate of baryta formed, and the filtrate treated with ammonia and oxalate of ammonia. If _lime_ be present,--although its sulphate is not easily soluble--sufficient will be contained in the filtrate to give a white precipitate of oxalate of lime.

The remaining portion of the solution is evaporated to dryness, and the residue treated with absolute alcohol. Chloride of strontium goes into solution, chloride of barium remaining undissolved. If upon evaporating the alcoholic solution a residue is obtained which, when dissolved in water, produces turbidity in a solution of sulphate of lime, _strontia_ is present.

The residue, insoluble in alcohol, is dissolved in water. If a precipitate is produced by the addition of sulphuric acid or hydrofluosilicic acid to the solution, _baryta_ is present. The latter reaction distinguishes baryta from strontia, which is not precipitated by hydrofluosilicic acid. Should the tests mentioned above fail to give affirmative results, and poisoning by means of baryta and strontia be nevertheless suspected, these compounds may possibly have remained in the materials contained in the alimentary canal, in the state of insoluble sulphates. To effect their detection under these circumstances the organic substances must be decomposed by means of sulphuric acid. The carbonaceous residue is calcined in a crucible at an elevated temperature, and the remaining mass treated with water. In this way, a solution of sulphides of barium and strontium is obtained, which is then tested as directed above.

DETECTION OF CHLORINE, BROMINE, AND IODINE.

CHLORINE AND BLEACHING CHLORIDES.

The detection of chlorine is very difficult owing to the great tendency it possesses to become converted into chlorides or hydrochloric acid, and it is only when found in a free state that its discovery is of importance.

In case the gas exists uncombined in the alimentary canal, its odor will be perceptible, and, upon boiling the suspected materials with water, vapors will be evolved which impart a blue color to paper saturated with a mixture of iodide of potassium and starch paste. If the addition of sulphuric acid is necessary in order to produce the above reactions, there is reason to suspect the presence of "chloride of lime" or "_Eau de Javelle_."[J]

[J] The so-called "chloride of lime" is probably either a mixture of
chloride and hypochlorite of calcium or an oxydichloride of the metal;
"_Eau de Javelle_" is the corresponding potassium compound.--_Trans._

BROMINE.

In case bromine exists in a free state at the time the autopsy is made, its presence will be detected by the reddish color and unpleasant odor it possesses. Its isolation is accomplished by treating the materials with bisulphide of carbon which, upon dissolving the bromine, acquires a red color. If potassa is then added to the solution, it combines with the bromine and, upon evaporating the decanted fluid, calcining the residue, and treating it with water, a solution of bromide of potassium is obtained. Upon adding chlorine-water and ether to a portion of the fluid, and shaking the mixture, the bromine is liberated and is dissolved by the ether. The etherial solution of bromine, which possesses a reddish-yellow color, does not mingle with, but floats upon the surface of the colorless aqueous solution.

If nitrate of silver is added to another portion of the aqueous solution of bromide of potassium, a precipitate of bromide of silver, soluble in ammonia, is formed.

In case the bromine has been converted into a bromide, it is necessary to boil the alimentary canal and the articles of food contained therein with water. The fluid is next filtered and agitated with chlorine-water and ether. The liberated bromine is dissolved by the ether, which acquires a reddish-yellow color. Upon decanting the solution, and treating it with potassa, bromide of potassium is formed, and can be detected as directed above.

IODINE.

The detection of iodine is accomplished by a process almost identical with the above. The isolation of the iodine having been effected, it remains to be ascertained that it imparts a blue color to starch paste, and a violet color to bisulphide of carbon.

DETECTION OF METALS.

Under this head we will indicate the systematic course of analysis to be pursued, supposing a mixture of several metals including arsenic and antimony, to be under examination.

The organic substances are first destroyed by means of chlorate of potassa and hydrochloric acid. When this is accomplished, the excess of chlorine is removed by boiling and the liquid filtered. The portion remaining on the filter is preserved: it contains all the silver and a large portion of the lead, if these metals are present. We will designate the residue as A, the filtrate as B.

TREATMENT OF RESIDUE A.

The residue is calcined with a little carbonate of soda and cuttings of pure Swedish filtering paper, the chlorides present being reduced to the metallic state by this treatment. The residue is next taken up with water acidulated with nitric acid, and the solution filtered. An insoluble residue, that may remain, is washed with hot water until the wash-water ceases to precipitate solution of nitrate of silver, and dried. It is then dissolved in boiling nitric acid, the solution diluted with water, and filtered.[K]

[K] If an insoluble residue remains by the treatment with nitric
acid, it may consist of _tin_. In this case, it is dissolved in _aqua
regia_, the metal precipitated by immersing a plate of zinc in the
solution and then re-dissolved in boiling hydrochloric acid. Upon
adding chloride of gold to the solution so obtained, a purple
precipitate is formed. Sulphuretted hydrogen produces a brown
precipitate, soluble in sulphide of ammonium, in presence of tin.

Sulphuric acid is added to the filtrate: if no precipitate forms, the absence of _lead_, in the residue A, is indicated. If, on the contrary, a precipitate is produced, it is collected upon a filter and washed. In order to make sure that the precipitate consists of sulphate of lead, it is treated with a solution of tartrate of ammonia: it should dissolve, forming a solution in which sulphuretted hydrogen produces a black precipitate.

The fluid which has failed to be precipitated by the addition of sulphuric acid, or the filtrate separated from the precipitate formed, can contain only silver. Upon adding hydrochloric acid, this metal is thrown down as a caseous white precipitate, which is soluble in ammonia, but insoluble in boiling nitric acid, and blackens upon protracted exposure to light. The formation of a precipitate possessing these properties, leaves no doubt as to the presence of _silver_.

_Remark._--In the operations described above, as well as in those following, the difficulty in separating minute precipitates from the filter is often experienced. When the precipitate is to be dissolved in reagents that do not affect the paper, such as ammonia, tartrate of ammonia, and dilute acids, it can be brought in solution directly on the filter. In cases, however, where reagents which attack the paper are employed, the precipitate should be separated. This is accomplished by mixing a small quantity of pure silica, obtained by the decomposition of fluoride of silicium by water, with the solution, before filtering. The precipitate becomes intimately mixed with the silica, and can then be readily removed from the paper. The presence of silica does not interfere, it being insoluble in the reagents commonly made use of.

TREATMENT OF FILTRATE B.

A current of sulphuretted hydrogen is conducted for twelve hours through the solution, which is kept at a temperature of 70°. by means of a water-bath. The flask containing the liquid is then closed with a piece of paper, and allowed to remain in a moderately warm place until the odor of the gas is no longer perceptible. The solution is next filtered with the precaution mentioned in the preceding remark, and the precipitate (_a_) thoroughly washed. The water used in this operation is united to the filtrate, and the fluid (_b_) examined as directed further on.

TREATMENT OF PRECIPITATE _a_.

In order to free the precipitate from the organic substances possibly present, at the same time avoiding a loss of any metal, it is dried, moistened with nitric acid, and the mass heated on a water-bath. Some Swedish filtering paper is next added, the mixture well impregnated with sulphuric acid, and then maintained for several hours at a temperature of about 170°. until a small portion (afterwards returned) gives a colorless solution when treated with water. The residue is now heated with a mixture of one part of hydrochloric acid and eight parts of water, the liquid filtered, the matter remaining undissolved washed with dilute hydrochloric acid, and the washings united with the filtrate.

The residue I. and the solution II. are separately examined as directed below.

RESIDUE I.

This may contain lead, mercury, tin, bismuth and antimony. It is heated for a considerable time with _aqua regia_, the solution filtered, and the second residue, should one remain, washed with dilute hydrochloric acid. If the second residue is fused with cyanide of potassium, the compounds present are reduced to the metallic state. The liberated metals are treated with nitric acid, which dissolves _lead_, but leaves _tin_ as insoluble metastannic acid. The nitrate of lead is then filtered from the metastannic acid, and both metals are identified as described in the treatment of residue A.

The solution, obtained by the action of _aqua regia_ on residue I, is treated with sulphuretted hydrogen. The tin and antimony are separated from the lead, mercury and bismuth by treating the precipitate produced with sulphide of ammonium, which dissolves only the sulphides of the first two metals. The solution in sulphide of ammonium is afterwards examined for these metals, as directed under the head of solution IV., the search for arsenic, however, being here omitted.

Upon treating the residue insoluble in sulphide of ammonium with nitric acid, lead, copper and bismuth go into solution, mercury remaining undissolved. The liquid is filtered, and the undissolved mercury submitted to the special examination previously described.

Sulphuric acid is added to the solution and the precipitate of sulphate of lead formed, separated, washed, and examined as directed while treating of residue A.

Finally, the solution separated from the lead is tested for _bismuth_ and _copper_, as in examination of precipitate III.

SOLUTION II.

The solution is concentrated by heating on a water-bath, a small quantity of carbonate of soda cautiously added to a portion, and notice taken if a precipitate forms. The part taken is then acidulated with a little hydrochloric acid, returned to the principal solution, and sulphuretted hydrogen conducted through the fluid, as in the examination of solution B. In case a precipitate fails to form, all metals are absent; if, on the contrary, a precipitate (_c_) is produced, it is examined as directed below.

EXAMINATION OF PRECIPITATE _c_.

If the solution merely became turbid, or the precipitate formed was of a pure white color, it consists probably of sulphur. It is, however, indispensable, even in this case, to collect the precipitate and examine it for _arsenic_. Provided it is of a pure yellow color, it is treated with ammonia. In case it is entirely dissolved by this treatment, and the addition of carbonate of ammonia failed to produce a precipitate in solution II., it is certain that arsenic, and no other metal, is present. Under these circumstances, the ammoniacal solution is examined as directed in the article on the detection of arsenic. If, on the other hand, the precipitate is not yellow, or being yellow, is but imperfectly soluble in ammonia, and a precipitate was formed by the addition of carbonate of ammonia to solution II., it is necessary to likewise search for tin, antimony, mercury, copper, bismuth and cadmium. In this case, the precipitate is placed in a small flask, allowed to digest for several hours with ammonia and sulphide of ammonium in a moderately warm place, and the solution filtered.

The remaining residue (III.) is washed, labelled, and preserved for subsequent examination; the _filtrate_ (IV.) is treated as directed below.

TREATMENT OF SOLUTION IV.

The solution, to which the water used in washing the residue has been added, is evaporated to dryness, the residue obtained taken up with pure fuming nitric acid, and the liquid again evaporated. The second residue is next saturated with a solution of carbonate of soda. A mixture of 1 part of carbonate and 2 of nitrate of soda is then added, the mixture evaporated to dryness, and the residual mass heated to fusion. The fused mass, when cold, is treated with cold water, and any remaining residue washed with a mixture of equal parts of alcohol and water. The filtered fluids are now evaporated in order to remove the alcohol, sulphuric acid is then added, and the mixture heated until white fumes of the acid begin to evolve. In this way the complete expulsion of the nitric acid present is rendered certain. When cold, the residue is treated with water and the _solution_ introduced into Marsh's apparatus, or, in case a quantitative estimation of the arsenic is desired, it is treated with sulphuretted hydrogen and the weight of the precipitate formed determined, as directed under the detection of arsenic.

Should a residue insoluble in water remain, it may contain tin, antimony and traces of copper. Upon dissolving it in _aqua regia_ and placing a sheet of pure zinc in the solution, these metals are thrown down in the metallic state. The precipitate is collected, the zinc present completely removed by treatment with _dilute_ hydrochloric acid, and the residue boiled with concentrated hydrochloric acid which dissolves the _tin_ present. The fluid is filtered and the _filtrate_ tested for this metal by adding solution of chloride of gold, which, in its presence, produces a purple precipitate, and, by treating it with sulphurated hydrogen, which forms a brown precipitate, soluble in sulphide of ammonium.

If the _residue_, insoluble in concentrated hydrochloric acid, is thoroughly washed and then treated with nitric acid, the copper present goes in solution. The fluid is filtered, and ammonia added to the filtrate: in presence of _copper_, the solution acquires a blue color, and gives a reddish precipitate upon addition of ferrocyanide of potassium.

_Antimony_, if present, remains by the treatment with nitric acid as an insoluble intermediate oxide. This is dissolved in hydrochloric acid, in which it is now soluble, and the solution introduced into Marsh's apparatus.

TREATMENT OF PRECIPITATE III.

This precipitate may contain the sulphides of mercury, copper, cadmium and bismuth. Upon treating it with nitric acid, all but the sulphide of mercury are dissolved. In case no residue remains, the absence of _mercury_ is indicated; if, on the other hand, a residue is left, it is well washed, dissolved in _aqua regia_, and the solution examined, either by means of Smithson's pile, or in the apparatus of Flandin and Danger. (_Vide Detection of Mercury._)

Whether a residue remains or not, an excess of ammonia is next added to the filtered solution in nitric acid: the formation of a permanent precipitate denotes the presence of _bismuth_. In this case, the fluid is filtered, and the alkaline filtrate further tested for copper and cadmium. For this purpose, cyanide of potassium is added, and sulphuretted hydrogen conducted through the filtrate: if _cadmium_ be present, a yellow precipitate is produced, copper not being thrown down in presence of an alkaline cyanide. The precipitate of sulphide of cadmium is separated from the solution by filtration, and the filtrate saturated with hydrochloric acid. _Copper_, if present, is now precipitated as sulphide: its separation is completed by conducting sulphuretted hydrogen through the fluid.

The precipitate is collected, washed, dissolved in nitric acid, and its identity established as previously directed. If the metal be present in sufficient quantity, it should be obtained in a metallic state upon a plate of iron; it is then coherent, possesses its natural color, and can conveniently be exhibited to the Jury.

TREATMENT OF SOLUTION _b_.

This solution may contain: cobalt, nickel, iron, manganese, chromium, zinc and aluminium. Of these, only zinc and chromium are poisonous; the search for these two metals is therefore all that is necessary in criminal cases. The solution is treated with a slight excess of ammonia, sulphide of ammonium added, and the fluid, after being allowed to stand for several hours, filtered. The precipitate may consist of sulphide of zinc and hydrated oxide of chromium, as well as of traces of sulphide of iron and phosphate of lime. If the suspected materials contained a _chromate_, this salt, in presence of hydrochloric acid and sulphuretted hydrogen, would be converted into sesquichloride of chromium a compound which is precipitated by sulphide of ammonium as a hydrated oxide.

The precipitate is washed with water, to which a little sulphide of ammonium is added, then dried, and fused with four times its weight of a mixture of equal parts of carbonate and nitrate of potassa. After the mass has remained in a state of fusion for a quarter of an hour, it is treated with boiling water, mixed with a little alcohol, in order to decompose the manganate that would be present were manganese contained in the materials under examination. The alcohol is then expelled by boiling the fluid, and the solution filtered. The _filtrate_ may contain phosphate of potassa, originating from the phosphate of lime present, and _chromate of potassa_, resulting from the oxidation of the sesquioxide of chromium. In presence of the latter compound, the following reactions will occur in the solution: 1st., Upon acidulation with acetic acid and addition of solution of acetate of lead, a yellow precipitate, soluble in potassa, is formed; 2nd., if hydrochloric acid is added and sulphuretted hydrogen conducted into the solution, the latter acquires a green color, and, upon adding ammonia, a bluish-grey precipitate of chromic hydrate is produced; 3rd., if nitrate of silver is added to the solution, a brick-red precipitate is formed.

The _precipitate_ remaining on the filter, may consist of zinc, mixed with the oxides of iron, nickel, cobalt, aluminium and manganese. It is dissolved in boiling hydrochloric acid, acetate of soda added, and the fluid boiled until no further precipitation occurs. The iron is now completely separated. The solution is then filtered, the precipitate washed, and an excess of potassa added to the _filtrate_; if the solution contains cobalt, nickel or manganese--which is improbable--a permanent precipitate is formed. This is separated from the fluid by filtration: its further examination is, however, unnecessary, as the metals of which it consists are not poisonous. The _filtrate_ may contain aluminium and _zinc_. The latter metal is detected by acidulating the filtrate with acetic acid, and adding a solution of sulphuretted hydrogen: in presence of zinc a white precipitate of its sulphide is formed.

In case organic substances are present, the precipitation of chromium by sulphide of ammonium may possibly have been hindered, and the metal have passed into the filtrate. When, therefore, chromium is not detected in the precipitate, the filtrate should also be examined. For this purpose, the fluid is evaporated to dryness, and the residue obtained fused with a mixture of nitrate and carbonate of soda. The fused mass is then taken up with water, the solution acidulated with acetic acid, and a solution of acetate of lead added: if chromium be present, a yellow precipitate, soluble in potassa, is produced.

DETECTION OF ALKALOIDS AND SOME ILL-DEFINED ORGANIC SUBSTANCES.[L]

A general method for effecting the detection of alkaloids was first proposed by _Stas_. Since the publication of this method, modifications to it have been recommended by _Otto_, and by _L. Uslar_ and _J. Erdman_. Other processes have been suggested by _Rodgers_ and _Girwood_, by _E. Prollius_, and by _Graham_ and _Hofman_. The latter will doubtless become general in their application; but up to the present time they have been employed exclusively in the detection of strychnine. Dialysis has also been recently applied in the separation of alkaloids.

[L] Colchicine, picrotoxine and digitaline.

STAS'S METHOD.

This method is based upon the facts: (_a_), that the acid salts of the alkaloids, especially those containing an excess of tartaric or oxalic acids, are decomposed by caustic alkalies and by the bicarbonates of soda and potassa; (_b_), that the alkaloids, when liberated in this manner, are combined with a certain amount of water which determines their solution in ether, although, in a desiccated state they may be insoluble in this menstruum; (_c_), that they may be extracted from their aqueous solutions by agitation with ether.

Stas's original method is as follows: The suspected substances, if organs are contained, are cut into fine shreds, then mixed with absolute alcohol, 0.5 to 2. grammes of tartaric or oxalic acid added and the whole introduced into a flask and heated at a temperature of 60° to 75°. When quite cold, the mixture is filtered, and the undissolved portion remaining on the filter washed with absolute alcohol, the washings being added to the filtrate. The alcoholic solution is evaporated, either by placing it under a bell-jar connected with an air-pump, or by passing a current of air, having a temperature not exceeding 35° over it, until reduced to a quarter of its original volume: the complete expulsion of the alcohol being then rendered certain. If insoluble matter separates during this operation, the concentrated fluid is passed through a moistened filter, the water used in washing the residue being united to the filtrate which is then evaporated to dryness by aid of the air-pump or by placing the fluid in a bell-jar over concentrated sulphuric acid. When the evaporation is completed, the residue is treated with absolute alcohol, the alcohol allowed to evaporate at the ordinary temperature of the air, and the second residue dissolved in the smallest possible amount of water. The fluid thus obtained is placed in a test-tube, and a concentrated solution of bicarbonate of soda added so long as effervescence takes place. Ether is then added, the mixture thoroughly shaken, and after it has remained at rest for some time, a small portion of the supernatant ether removed and evaporated on a watch-glass: the residue obtained will consist of the alkaloid present. Two cases are now possible: the alkaloid is a solid, or it is a liquid and is volatile.

The further treatment of the solution is modified according to these circumstances.

_a._ THE ALKALOID IS LIQUID AND VOLATILE.

If, upon the evaporation of the ether, oily streaks were left on the watch-glass, a volatile alkaloid is probably present.

In this case, a solution of caustic potassa is added to the test-tube, the mixture shaken, the supernatant ether decanted[M] into a flask and the remaining solution again washed with ether until the last portion fails to leave a residue upon evaporation. The etherial fluids are then united, and two cubic centimetres of water, acidulated with one-fifth of its weight of sulphuric acid, added. This acid retains the alkaloid, which is now in the state of a pure acid-sulphate soluble in water, the animal matters present remaining dissolved in the ether. The ether, in which some sulphate of conia may be contained--although the greater portion of this compound would remain in the aqueous solution--is then decanted. The remaining aqueous solution of the pure sulphate of the alkaloid is placed in a test-tube, a solution of caustic potassa and some ether added, and the mixture well shaken. The ether is next decanted and allowed to spontaneously evaporate in a dry place at a very low temperature, and the ammonia possibly present is then removed by placing the vessel containing the residue over sulphuric acid. The residue now obtained consists of the alkaloid present in a state of purity, and can be directly identified by means of the reactions described further on.

[M] The necessity of decanting etherial and other solutions is
advantageously obviated by the use of a pipette.--_Trans._

_b._ THE ALKALOID IS SOLID.

It sometimes occurs that ether fails to take up all of the alkaloid present in the fluid treated with bicarbonate of soda. Under these circumstances the fluid should be mixed with caustic potassa, the mixture shaken, and the ether decanted; this operation being repeated several times, until the entire amount of the alkaloid is removed; the ethereal fluids are then united in a capsule, and allowed to spontaneously evaporate. The result of the evaporation may be solid; more frequently, however, a milky liquid remains which restores the blue color to reddened litmus paper; if so, the presence of a vegetable alkaloid is certain. In order to purify the residue, a few drops of water, slightly acidulated with sulphuric acid, are added to the capsule, and the latter turned, so as to bring the fluid in contact with the substance at all points; in this manner a colorless and limpid fluid is obtained, the fatty substances adhering to the dish. The liquid is decanted into a second capsule, the remaining residue washed with a little acidulated water, and the washings likewise added to the principal solution. The fluid is now evaporated either _in vacuo_, or over sulphuric acid, to about three-fourths of its original volume a concentrated solution of neutral carbonate of potassa added, and the mixture treated with absolute alcohol, which dissolves the liberated alkaloid, and separates it from the sulphate of potassa formed and the excess of carbonate of potassa. The alcoholic solution is decanted and allowed to evaporate _in vacuo_ or in the air: the alkaloid now crystallizes out in a state suitable for further examination.

MODIFICATIONS TO STAS'S METHOD, PROPOSED BY OTTO.

In Stas's method, the loss of morphine is possible, for, if ether is not added immediately after the addition of carbonate of soda, this alkaloid crystallizes and is then no longer soluble in that menstruum; and, if the ethereal solution is not quickly decanted, the portion dissolved will likewise separate out in small crystals. In both cases, morphine will remain in the aqueous solution from which the other alkaloids have been extracted by the ether. _M. Otto_ recommends the addition of chloride of ammonium and a little soda-lye, in order to dissolve the alkaloid. Upon allowing the solution so obtained to stand for some time exposed to the air, crystals of morphine are deposited.

According to the same authority, it is advisable to omit the distinction drawn by Stas between volatile and fixed alkaloids, and submit both to the treatment recommended for those that are volatile.

Otto also recommends the agitation of the fluid containing the oxalates or tartrates of the alkaloids with ether, previously to their separation by means of bicarbonate of soda. By this treatment the elimination of the coloring matter present--as well as of _colchicine_, _digitaline_, _picrotoxine_, traces of _atropine_, and various impurities--is accomplished. As soon as the ether ceases to become colored and to leave a residue upon evaporation, alkali is added, and the operation concluded as usual. In this way the alkaloid is obtained, almost directly, in a pure condition. This last modification appears to us to be a very happy one, inasmuch as it greatly facilitates the purification of the alkaloid present.

MODIFICATIONS TO STAS'S METHOD, PROPOSED BY USLAR AND ERDMAN.

1st. The materials to be examined are brought to the consistence of a thin paste, and digested for about two hours with water, to which some hydrochloric acid has been added, at a temperature of 60° to 80°. The mixture is then filtered through a moistened linen cloth, and the residue washed with warm acidulated water; the washings being added to the solution.

2nd. Some pure quartz sand--or, preferably, silica prepared by the decomposition of fluoride of silicium--is added to the filtrate, the fluid supersaturated with ammonia, and evaporated to dryness over a water-bath: the addition of silica renders the residue friable.

3rd. The residue is boiled repeatedly with amylic alcohol, which extracts all the alkaloid present as well as the fatty and coloring matters, and the extracts filtered through filter paper that has been moistened with amylic alcohol.

4th. The filtered fluid is thoroughly agitated with ten or twelve times its volume of almost boiling water acidulated with hydrochloric acid: the hydrochlorate of the alkaloid present goes into the aqueous solution, the fatty and coloring substances remaining dissolved in the oily supernatant layer. The latter is separated by means of a pipette, and the acid aqueous solution shaken with fresh quantities of amylic alcohol until completely decolorized.

5th. The aqueous solution is then concentrated, ammonia added, and the mixture well shaken with warm amylic alcohol, in which the alkaloid dissolves. As soon as the solution forms a supernatant layer upon the surface of the fluid, it is drawn off with a pipette and evaporated on a water-bath. In this manner, the alkaloid is usually obtained in a sufficient state of purity to admit of its immediate identification; if, however, a small portion turns brown when treated with concentrated sulphuric acid, the process of purification must be repeated. Under these circumstances it is re-dissolved in dilute hydrochloric acid, the solution repeatedly shaken with amylic alcohol, in order to extract the impurities present, and the alkaloid then extracted with ammonia and amylic alcohol, as previously directed.