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Other Reactions.-Add to small quantities of aqueous solution of albumen solutions of corrosive sublimate, nitrate of silver, sulphate of copper, acetate of lead, alum, perchloride of tin, &c.; the various salts not only coagulate but form insoluble compounds with albumen. Hence the value of an egg as a temporary antidote in cases of poisoning by many metallic salts, its administration retarding the absorption of the poison until the stomach-pump or other measures can be applied. Sulphuric, nitric, and hydrochloric acids precipitate albumen; the coagulum is slowly redissolved by aid of heat, a brown, yellow, or purplishred colour being produced. Neither acetic, tartaric, nor organie acids generally, except gallo-tannic, coagulate albumen. Alkalies prevent the precipitation of albumen.

Albumen is met with in large quantity in the serum of blood, in smaller quantity in chyle and lymph, and in the brain, kidneys, liver, muscles, and pancreas. It is not a normal constituent of saliva, gastric juice, bile, or mucus, but occurs in those secretions during inflammation. It is found in the urine and fæces only under certain diseased states of the system.

The cause of the coagulation of albumen by heat &c. cannot at present be explained.

Albumen has not yet been obtained sufficiently pure to admit of its composition being expressed by a trustworthy formula; Gerhardt regarded it as a sodium compound (HNAC,,H110N18SO229 H2O).

72

TOXICOLOGICAL OPERATIONS.

In cases of murder, suicide, and accidental poisoning, the substances presented to the chemical analyst for examination are usually articles of food, medicines, vomited matters, or the liver, kidney, stomach and contents, removed in course of post-mortem examination. In these cases some special operations are necessary before the poison can be isolated in a state of sufficient purity for the application of the usual tests; for in most instances the large quantity of animal and vegetable, or, in one word, organic matter present prevents or masks the characteristic reactions on which the tests are founded. These operations will now be described *; they form the chemical part of the subject of Toxicology (TožɩKòv, toxicon, poison, and λoyos, logos, discourse). Substances occurring in the form of an apparently definite salt or unmixed with organic matter need no special treatment, they are analyzed by the ordinary methods already given, attention being restricted, of course, to poisonous compounds only.

EXAMINATION OF AN ORGANIC MIXTURE SUSPECTED TO CONTAIN MERCURY, ARSENICUM, ANTIMONY, LEAD, OR COPPER, SULPHURIC ACID, NITRIC ACID, HYDROCHLORIC ACID, OXALIC ACID, OR HYDROCYANIC ACID, STRYCHNINE OR MORPHINE.

Odour, Appearance, Taste.-Smell the mixture with the view of ascertaining the presence or absence of any notable quantity of free hydrocyanic acid. Look carefully for any small solid particles, such as arsenic, corrosive sublimate, verdigris, &c., and for any appearance which may be regarded as abnormal, any character unusual to the coffee, tea, beer, medicine, vomit, coats of stomach, kidney, liver, or other organ, tissue, or solid matter under examination. If liquid or semifluid, taste the mixture,

* Materials for these experiments are readily obtained for educational purposes by dissolving the poison in infusions of tea, coffee, porter, or in water to which some mucilage of starch or linseed-meal, pieces of bread, potato, fat, &c. have been added.

or add to a small portion some solution of carbonate of sodium with the view of ascertaining by excessive sourness or strong effervescence the presence of any large poisonous quantity of sulphuric, nitric, or hydrochloric acids.

If this preliminary examination does not indicate the method to be pursued, proceed as follows, treating a portion, not more than one-fourth, of the mixture for the poisonous metals, another for the acids, and a third for alkaloids, reserving the remainder for any special experiments which may suggest themselves in the course of the analysis.

Examination for Mercury, Arsenicum, Antimony, Lead, Copper.

If a liquid, acidulate with hydrochloric acid and boil for a short time. If solid or semisolid, cut up the matter into small pieces, add enough water to form a fluid mixture, with from onefourth to one-tenth of its bulk of hydrochloric acid, and boil until, from partial aggregation, solution, &c. of the solid matter, filtration can be easily effected.

Heat a portion of the clear liquid with a thin piece of bright copper or copper gauze, about an inch long and a quarter of an inch broad, for about ten or twenty minutes; metallic mercury, arsenicum, or antimony will be deposited on the copper, darkening it considerably in colour. Pour off the liquid from the copper, carefully rinse the latter with a little cold water, dry the piece of metal by holding it over or near a flame (using fingers, not tongs, or it may become sufficiently hot for loss of mercury or arsenicum to occur by volatilization), introduce it into a narrow test-tube or piece of glass tubing closed at one end, and heat the bottom of the tube in a flame, holding it horizontally, that the upper part of the tube may be kept cool, and closing the mouth of the tube with the finger to prevent escape of vapour. Under these circumstances any Mercury will volatilize from the copper and condense on the cool part of the tube in a ring or patch of

white sublimate, readily aggregating into visible globules on being pressed by the side of a thin glass rod inserted into the tube; Arsenicum will volatilize from the copper, and, absorbing oxygen from the air in the tube, condense on the cool part of the glass in a ring or patch of white sublimate of arsenic, not running into globules when rubbed, but occurring in small crystals, the characteristic octahedral form of which is readily seen by aid of a good hand lens, or the low power of a microscope; Antimony volatilizes from the copper, if strongly heated, and, absorbing oxygen, immediately condenses as a slight white deposit close to the metal.

Nothing short of the production of globules should be accepted as evidence of the presence of mercury. It will usually have

existed as corrosive sublimate.

To confirm indications of the presence of arsenicum, a portion of the acid liquid may be subjected to the hydrogen tests; or the tube containing the white crystalline arsenic may be broken, and the part on which the sublimate occurs boiled for some time in water, and the hydrosulphuric-acid, ammonio-nitrate-of-silver, or ammonio-sulphate-of-copper test applied to the aqueous solution.

For antimony, a portion of the acid liquid must always be introduced into the hydrogen-apparatus with the usual precautions. (Vide p. 101.)

For lead and copper, pass hydrosulphuric acid gas through the clear acid liquid for some time, warming the liquid if no precipitate is produced, or diluting and partially neutralizing the acid by ammonia if much acid has been added. Collect on a filter any black precipitate that may have formed; wash, dissolve in a few drops of aqua regia, dilute, and apply the tests of ammonia for copper, sulphuric acid for lead, and any other of the ordinary reagents.

Copper may often be at once detected in a small quantity of acidulated liquid by immersing the point of a penknife or a piece

of bright iron wire,-a deposit of copper in its characteristic colour quickly or slowly appearing, according to the amount present.

Examination for Mineral Acids, Oxalic Acid, or Hydrocyanic

Acid.

To detect sulphuric, nitric, or hydrochloric acids in any liquid containing organic matter, dilute with water and apply to small portions the usual tests for each acid, disregarding indications of small quantities.

Excessive sourness, copious evolution of carbonic acid gas on the addition of carbonate of sodium, and abundant evidence of acid on applying the various tests to small portions of the fluid presented for analysis, collectively form sufficient evidence of the occurrence of a poisonous amount of either of the three common mineral acids. Small quantities of the sulphuric, nitric, and hydrochloric radicals occurring as metallic salts or acids, are common normal constituents of food, hence the direction to disregard insignificant indications. If the fluid under examination is a vomit or the contents of a stomach, and an antidote has been administered, free acid will not be found, but, instead, a large amount of some particular salt.

For oxalic acid, filter or strain a portion of the liquid, if not already clear, and add solution of acetate of lead so long as a precipitate occurs; collect the precipitate, which is partly oxalate of lead, on a filter, wash, transfer it to a test-tube or test-glass, add a little water, and pass hydrosulphuric gas through the mixture for a short time; the lead is thus converted into the insoluble form of sulphide, while oxalic acid is set free in the solution. Filter, boil to get rid of hydrosulphuric gas, and apply the usual tests for oxalic acid (see p. 207) to the clear filtrate.

For hydrocyanic acid, the three chief tests may be applied at once to the liquid or semiliquid organic mixture, whether it has an odour of hydrocyanic acid or not. First:-half fill a small porcelain crucible with the mixture, add eight or ten drops

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