addition of some hydrochloric acid: this will indicate the degree 2. Preparation and Examination of the Acid Extract. § 215. 1. Heat about 50 grammes of the soil from which the part soluble 274 in water-both cold and hot-has been removed as far as practicable* (see § 214), with moderately strong hydrochloric acid (effervescence indicates CARBONIC ACID) for several hours on the water-bath, filter, and make the following experiments with the filtrate, which, owing to the presence of sesquichloride of iron, has in most cases a yellow color :— Test a small portion of it with sulphocyanide of potassium for 275 SESQUIOXIDE OF IRON, another with ferrocyanide of potassium for PROTOXIDE OF IRON. 2. Test a small portion with chloride of barium for SULPHURIC ACID, another with molybdate of ammonia for PHOSPHORIC ACID. 3. Mix a larger portion of the filtrate with ammonia to neutra- 276 lize the free acid, then with yellowish sulphide of ammonium; and let the mixture stand in a warm place until the fluid looks yellow; then filter, and test the filtrate in the usual way for LIME, MAGNESIA, POTASSA, AND SODA. 4. Dissolve the precipitate obtained in 3 (276), in hydrochloric 277 acid, evaporate the solution to dryness, moisten the residue with hydrochloric acid, add water, warm, filter, and examine the filtrate according to the directions of § 192, 2 (150), for IRON, MANGANESE, ALUMINA, and, if necessary, also for lime and magnesia, which may have been thrown down by the sulphide of ammonium, in combination with phosphoric acid. 5. The separated SILICIC ACID obtained in 4 is usually colored by organic matter. It must, therefore, be ignited to obtain it pure. 6. If it is a matter of interest to ascertain whether the hydro- 278 chloric acid extract contains ARSENIC ACID, OXIDE OF COPPER, &c., treat the remainder of the solution first with sulphite of soda, then with hydrosulphuric acid, as directed in § 223, 1, and 2. 7. Should you wish to look for FLUORINE, ignite a fresh portion of the earth, and then proceed according to the directions of § 205. 3 (230). 3. Examination of the Inorganic Constituents insoluble in Water and Acids. The operation of heating the lixiviated soil with hydrochloric 279 acid (§ 215 [274]) leaves still the greater portion of it undissolved. If you wish to subject this undissolved residue to a chemical exami * Complete lixiviation is generally impracticable. nation, wash, dry, and sift, to separate the large and small stones from the clay and sand; moreover, separate the two latter from each other by elutriation. Subject the several portions to the analytical process given for the silicates (§ 203). 4. Examination of the Organic Constituents of the Soil.* § 217. The organic constituents of the soil, which exercise so great an influence upon its fertility, both by their physical and chemical action, are partly portions of plants in which the structure may still be recognised (fragments of straw, roots, seeds of weeds, &c.), partly products of vegetable decomposition, which are usually called by the general name of HUMUS, but differ in their constituent elements and properties, according to whether they result from the decay of the nitrogenous or non-nitrogenous parts of plants-whether alkalies.or alkaline earths have or have not had a share in their formation— whether they are in the incipient or in a more advanced stage of decomposition. To separate these several component parts of humus would be an exceedingly difficult task, which, moreover, would hardly repay the trouble; the following operations are amply sufficient to answer all the purposes of a qualitative analysis of the organic constituents of a soil. a. Examination of the Organic Substances soluble in Water. Evaporate the portion of the filtrate of 214, a (270), which has 280 been put aside for the purpose of examining the organic constituents, on the water-bath to perfect dryness, and treat the residue with water. The ulmic, humic, and geic acids, which were in the solution in combination with bases, remain undissolved, whilst crenic acid and apocrenic acid are dissolved in combination with ammonia; for the manner of detecting the latter acids, see § 212, 3 (268). b. Treatment with an Alkaline Carbonate. Dry a portion of the lixiviated soil, and sift to separate the 281 fragments of straw, roots, &c., together with the small stones, from the finer parts; digest the latter for several hours, at a temperature of 176°-194° F., with solution of carbonate of soda, and filter. Mix the filtrate with hydrochloric acid to acid reaction. If brown flakes separate, these proceed from ulmic acid, humic acid, or geic acid. The larger the quantity of ulmic acid present the lighter, the larger that of humic acid or geic acid, the darker the brown color of the flakes. c. Treatment with Caustic Alkali. Wash the soil boiled with solution of carbonate of soda (b) with 282 water, boil several hours with solution of potassa, replacing the water * Compare Fresenius' "Chemie für Landwirthe, Forstmänner und Cameralisten;" published at Brunswick, by F. Vieweg and Son, 1847, §§ 282—285. in proportion as it evaporates, dilute, filter, and wash. Treat the brown fluid as in b. The ulmic and humic acids which separate now, are new products resulting from the action of boiling solution of potassa upon the ulmine and humine originally present. V. DETECTION OF INORGANIC SUBSTANCES IN PRESENCE OF § 218. The impediments which the presence of coloring, slimy, and other organic substances throw in the way of the detection of inorganic bodies, and that the latter can often be effected only after the total destruction of the organic admixture, will be readily conceived, if we reflect that in dark colored fluids changes of color or the formation of precipitates escape the eye, that slimy fluids cannot be filtered, &c. Now, as these difficulties are very often met with in the analysis of medicinal substances, and more especially in the detection of inorganic poisons in articles of food or in the contents of the stomach, and, lastly, also in the examination of plants and animals, or parts of them, for their inorganic constituents, I will here point out the processes best adapted to lead to the attainment of the object in view, both in the general way and in special cases, 1. General Rules for the Detection of Inorganic Substances in Presence of Organic Matters, which by their Color, Consistence, &c., impede the Application of the Reagents, or obscure the Reactions produced. § 219. We confine ourselves here, of course, to the description of the most generally applicable methods, leaving the adaptation of the 'modifications which circumstances may require in special cases, to the discretion of the analyst. 1. THE SUBSTANCE UNDER EXAMINATION DISSOLVES IN WATER, BUT 283 THE SOLUTION IS DARK COLORED OR OF SLIMY CONSISTENCE. a. Boil a portion of the solution with hydrochloric acid, and gradually add chlorate of potassa, until the mixture is decolorized and perfectly fluid; heat until it no longer exhales the odor of chlorine, then dilute with water, and filter. Examine the filtrate in the usual way, commencing with § 188. Compare also § 223. b. Boil another portion of the solution for some time with nitric acid, filter, and test the filtrate for SILVER, POTASSA, and HYDROCHLORIC ACID. If the nitric acid succeeds in effecting the ready and complete destruction of the coloring and slimy matters, &c., this method is often altogether preferable to all others. c. ALUMINA and SESQUIOXIDE OF CHROMIUM might escape detection by this method, because ammonia and sulphide of ammonium fail to precipitate these oxides from fluids containing non-volatile organic substances. Should you have reason to suspect the presence of these oxides, deflagrate a third portion. of the substance with nitrate of potassa and some carbonate of The soda, and boil the fused mass with solution of soda. 2. BOILING WATER FAILS TO DISSOLVE THE SUBSTANCE, OR EFFECTS 284 ONLY PARTIAL SOLUTION; THE FLUID ADMITS OF FILTRATION. Filter, and treat the filtrate either as directed § 187, or, should it require decolorization, according to the directions of § 219, 1. The residue may be of various kinds. a. IT IS FATTY. Remove the fatty matters by means of ether, and should a residue be left, treat this as directed § 173. b. IT IS RESINOUS. Use alcohol instead of ether, or apply both liquids successively. c. IT IS OF A DIFFERENT NATURE, e.g., woody fibre, &c. a. Dry, and ignite a portion of the dried residue in a porcelain or platinum vessel, until total or partial incineration is effected; boil the residue with nitric acid and water, and examine the solution as directed § 187, III. (109); if a residue has been left, treat this according to the directions of § 201. B. Examine another portion for the heavy metals, in the manner directed § 219, 1, a; since in a, besides the compounds of mercury which may be present, arsenic, cadmium, zinc, &c., may volatilize. 7. Test the remainder for ammonia, by triturating it together with hydrate of lime. 3. THE SUBSTANCE DOES NOT ADMIT OF FILTRATION OR ANY OTHER 285 MEANS OF SEPARATING THE DISSOLVED FROM THE UNDISSOLVED PART. Treat the substance in the same manner as the residue in 2. As regards the charred mass (2 a), it is often desirable to boil the mass, carbonized at a gentle heat, with water, filter, examine the filtrate, wash the residue, incinerate it, and examine the ash. 2. Detection of Inorganic Poisons in Articles of Food, in Dead § 220. The chemist is sometimes called upon to examine an article of 286 food, the contents of the stomach of an individual, a dead body, &c., with a view to detect the presence of some poison, and thus to establish the fact of a wilful or accidental poisoning; but it is more frequently the case that the question put to him is of a less general nature, and that he is called upon to determine whether a certain substance placed before him contains a metallic poison; or, more pointedly still, whether it contains arsenic, or hydrocyanic acid, or some other particular poison-as it may be that the symptoms * Compare: a. Fresenius, "die Stellung des Chemikers bei gerichtlich chemischen Untersuchungen," &c. (Annal. der Chemie und Pharm. 49, 275); and b. Fresenius and v. Babo's " Abhandlung über ein neues, unter allen Umständen sicheres Verfahren zur Ausmittelung und quantitativen Bestimmung des Arsens bei Vergiftungsfällen."—Annal. der Chemie und Pharmacie, 49, 287. point clearly in the direction of that poison, or that the examining magistrate has, or believes he has, some other reason to put this question. It is obvious that the task of the chemist will be the easier, the more special and pointed the question which is put to him. However, the analyst will always act most wisely, even in cases where he is simply requested to state whether a certain poison, e. g. arsenic, is present or not, if he adopts a course of proceeding which will not only permit the detection of the one poison specially named, the presence of which may perhaps be suspected on insufficient grounds, but will moreover inform him as to the presence or absence of other similar poisons. But we must not go too far in this direction either; if we were to attempt to devise a method that should embrace all poisons, we might unquestionably succeed in elaborating such a method at the writing-desk; but practical experience would but too speedily convince us that the intricate complexity inseparable from such a course, must necessarily impede the easy execution of the process, and impair the certainty of the results, to such an extent indeed, that the drawbacks would be greater than the advantages derivable from it. Moreover, the attendant circumstances permit usually at least a tolerably safe inference as to the group to which the poison belongs. Acting on these views, I give here, 1. A method which ensures the detection of the minutest traces of arsenic, allows of its quantitative determination, and permits at the same time the detection of all other metallic poisons. 2. A method to effect the detection of hydrocyanic acid, which leaves the substance still fit to be examined both for metallic poisons and for vegeto-alkalies. 3. A method to effect the detection of phosphorus, which does not interfere with the examination for other poisons. This Section does not, therefore, profess to supply a complete guide in every possible case or contingency of chemico-legal investigations. But the instructions given in it are the tried and proved results of my own practice and experience. Moreover, they will be found sufficient in most cases, the more so as I shall append to the Section on the vegeto-alkalies the description of a process by which the detection of these latter poisons in criminal cases may be effected. I. METHOD FOR THE DETECTION OF ARSENIC (WITH DUE REGARD TO THE POSSIBLE PRESENCE OF OTHER METALLIC POISONS. § 221. Of all metallic poisons arsenic is the most dangerous, and at the 287 same time the one most frequently used, more particularly for the wilful poisoning of others. And again, among the compounds of arsenic, arsenious acid (white arsenic) occupies the first place, because (1) It kills even in small doses; (2) It does not betray itself, or at least very slightly, by the taste; and (3) It is but too readily procurable. |