c. Examine a third portion according to §149, 7 for FLUORINE. d. The remainder is acidified with hydrochloric acid, and a small portion is tested with chloride of barium for SULPHURIC ACID; the rest of the solution is heated to 158° Fah., and tested for ARSENIC ACID by hydrosulphuric acid. If no precipitate is formed, the liquid-or if a precipitate separates, the filtrate from it-is evaporated to dryness, the residue is treated with hydrochloric acid and water, and the solution thus obtained is examined for PHOSPHORIC ACID by means of sulphate of magnesia, or a nitric solution of molybdate of ammonia (§ 145). C. SILICATES WHICH ARE PARTIALLY DECOMPOSED BY ACIDS. § 211. Most native rocks are mixtures of several silicates, of which 231 the one is often decomposed by acids, the other not. If such mixtures were analyzed by the same method as the absolutely insoluble silicates, the analyst would indeed detect all the elements present, but the analysis would afford no satisfactory insight into the actual composition of the rock. It is, therefore, advisable to examine separately those parts which show a different deportment with acids. For this purpose digest the very finely pulverized substance for some time with hydrochloric acid* at a very gentle heat, then filter off a small portion, evaporate the remainder to dryness, and expose to a temperature somewhat exceeding 212° F., with stirring, until no more, or very little hydrochloric acid vapor is evolved; let the residue cool, moisten it when cold with hydrochloric acid, heat gently with water, and filter. The filtrate contains the bases of the decomposed part of the mixed mineral; examine this as directed (222). Test the portion first filtered off according to (223) 7, and portions of the original substance for other acids according to (224). The residue contains, besides the silicic acid separated from the bases by the action of the hydrochloric acid, that part of the mixed mineral which has resisted the action of the acid. Boil this residue with an excess of solution of carbonate of soda, filter hot, and wash, first with hot solution of carbonate of soda, finally with boiling water. Treat the residuary undecomposed part of the mineral, from which the admixed free * [Evolution of hydrogen gas may be due, in certain trap rocks, to presence of finely-divided metallic iron.] [According to A. Müller, caustic soda must be employed instead of carbonate of soda for taking up silica.] silicic acid has thus been removed, according to the instructions given in § 210. In cases where it is of no consequence or interest to effect the separation of the silicic acid of the part decomposed by acids, you may omit the laborious treatment with carbonate of soda, and may proceed at once to the decomposition of the residue. III. ANALYSIS OF NATURAL WATERS. § 212. In the examination of natural waters the analytical process 232 is simplified by the circumstance that we know from experience the elements and compounds which are usually found in them. Now, although a quantitative analysis alone can properly inform us as to the true nature and character of a water, since the differences between the various waters are principally caused by the different proportions in which the several constituents are respectively present, a qualitative analysis may yet render very good service, especially if the analyst notes with proper care, whether a reagent produces a faint or distinctly marked turbidity, a slight or copious precipitate, since these circumstances will enable him to make an approximate estimation of the relative proportions in which the several constituents are present. I separate here the analysis of the common fresh waters (spring-water, well-water, brook-water, river-water, &c.) from that of the mineral waters, in which we may also include sea-water; for, although no well-defined limit can be drawn between the two classes, still the analytical examination of the former is necessarily far more simple than that of the latter, as the number of substances to be looked for is much more limited than in the case of mineral waters. A. ANALYSIS OF FRESH WATERS (SPRING-WATER, WELL- § 213. We know from experience that the substances to be had 233 regard to in the analysis of such waters are the following: a. BASES: Potassa, soda, ammonia, lime, magnesia, protoxide of iron. b. ACIDS, &c.: Sulphuric acid, phosphoric acid, silicic acid, carbonic acid, nitric acid, nitrous acid, chlorine. C. ORGANIC MATTERS. d. MECHANICALLY SUSPENDED SUBSTANCES: Clay, &c. The fresh waters contain indeed also other constituents besides those enumerated here, as may be inferred from the origin and formation of springs, &c., and as has, moreover, been fully established by the results of analytical investigations; but the quantity of such constituents is so trifling that they escape detection, unless hundreds of pounds of the water are subjected to the analytical process. I omit, therefore, here the mode of their detection, and refer to § 214. 1. Boil one to two litres of the carefully collected water in 234 a glass flask or retort to one-half. This generally produces a precipitate. Pass the fluid through a perfectly clean filter (free from iron and lime), wash the precipitate well, after having removed the filtrate, and then examine both as follows: a. Examination of the precipitate. The precipitate contains those constituents of the water 235 which were only kept in solution through the agency of free carbonic acid, or, as the case may be, in the form of bicarbonates, viz., carbonate of lime, carbonate of magnesia, hydrated sesquioxide of iron (which was in solution as bicarbonate of protoxide of iron, and precipitates upon boiling.as sesquioxide, and if phosphoric acid is present, also in combination with that acid), phosphate of lime; and besides, silicic acid, and sometimes also sulphate of lime, if that substance is present in large proportion; and clay which was mechanically suspended in the water. Dissolve the precipitate on the filter in the least possible quantity of dilute hydrochloric acid (effervescence indicates the presence of CARBONIC ACID), and mix separate portions of the solution:— a. With sulphocyanide of potassium: red coloration indicates the presence of IRON. 3. After previous boiling, with ammonia: filter, if 236 necessary, mix the filtrate with oxalate of ammonia, and let the mixture stand for some time in a warm place. The formation of a white precipitate indicates the presence of LIME-in the form of carbonate, or also in that of sulphate if sulphuric acid is detected in y. Filter, mix the filtrate again with ammonia, add some Chatin ("Journ. de Pharm. et de Chim.," 3 Sér. t. xxvii. p. 418) found iodine in all fresh-water plants, but not in land plants, a proof that the water of rivers, brooks, ponds, &c., contains traces, even though extremely minute, of metallic iodides. According to Marchand ("Compt. Rend.," t xxxi. p. 495), all natural waters contain iodine, bromine, and lithia. Van Ankum has demonstrated the presence of iodine in almost all the potable waters of Holland. And it may be affirmed with the same certainty that all, or at all events most, natural waters contain compounds of strontia, fluorine, &c. phosphate of soda, stir with a glass rod, and let the RIC ACID. S. Evaporate another portion to dryness, treat the 237 residue with hydrochloric acid and water, filter and test the filtrate for PHOSPHORIC ACID by means of molybdic acid or sesquichloride of iron and acetate of soda (§ 145). b. Examination of the filtrate. a. Mix a portion of the filtrate with a little hydro- 238 chloric acid and chloride of barium. The formation of a white precipitate, which makes its appearance at once or perhaps only after standing some time, indicates SULPHURIC ACID. 6. Mix another portion with nitric acid, and add nitrate of silver. A white precipitate or a white turbidity indicates the presence of CHLORINE. 7. Test a portion of the filtrate after acidifying with hydrochloric acid, for PHOSPHORIC ACID as in (237). 5. Evaporate another and larger portion of the filtrate until highly concentrated, and test the reaction of the fluid. If it is alkaline, and a drop of the concentrated clear solution effervesces when mixed on a watch-glass with a drop of acid, a CARBONATE of an alkali is present. Should this be the case, evaporate the fluid to perfect dryness, boil the residue with spirit of wine, filter, evaporate the alcoholic solution to dryness, dissolve the residue in a little water, and test the solution for NITRIC ACID* as directed § 162, 7, 8 or 9. ε. Mix the remainder of the filtrate with some chloride of ammonium, add ammonia and oxalate of ammonia, and let the mixture stand for a considerable time. The formation of a precipitate indicates the presence Filter, and test,— of LIME. * In many cases this circuitous but safe process is unnecessary, nitric acid being readily detected directly in the highly concentrated water. aa. A small portion with ammonia and phosphate of soda for MAGNESIA. bb. Evaporate the remainder to dryness, heat the residue to redness, remove the magnesia, which may be present (168) and test for POTASSA and soda, according to the directions of § 200. 2. Acidify a tolerably large portion of the filtered water 239 with pure hydrochloric acid, and evaporate nearly to dryness; divide the residue into 2 parts, and— a. Test the one part with hydrate of lime for AMMONIA (compare § 94, 3). b. Evaporate the other part to dryness, moisten with hydrochloric acid, add water, warm, and filter, if a resi due remains. The residue may consist of SILICIC ACID, and of CLAY which has been mechanically suspended in the water; these two substances may be separated from each other by boiling with solution of carbonate of soda. The precipitate is often dark-colored from the presence of organic substances; but it becomes perfectly white upon ignition. 3. Mix another portion of the water, fresh taken from the 240 well, &c., with lime-water. If a precipitate is thereby produced, FREE CARBONIC ACID or BICARBONATES are present. If the former (free carbonic acid) is present, no permanent precipitate is obtained when a larger portion of the water is mixed with only a small amount of lime-water, since in that case soluble bicarbonate of lime is formed. 4. A portion is examined for NITROUS ACID* by mixing with 241 iodide of potassium-starch-paste (1 part of pure KI. 20 parts starch and 500 parts of pure water) and pure dilute sulphuric acid, and observing whether a blue coloration is produced at once or in a few minutes (§ 161, 1). 5. To detect the presence of ORGANIC MATTERS, evaporate a 242 portion of the water to dryness, and gently ignite the residue: blackening of the mass denotes the presence of organic substances. If this experiment is to give conclusive results, the evaporation of the water, as well as the ignition of the residue, must be conducted in a glass flask or a retort. 6. To detect putrefying organic matters or other substances recognisable by the odor, a flask is filled two-thirds full of the water, closed with the palm of the hand, and vigorously shaken; the smell is then noted. If hydrosulphuric acid is perceived proceed according to § 215, 3. To examine for organic odors in presence of hydrosulphuric *Found by Schönbein in all rain and snow-waters. |