tion of the alcoholic fluid is tested at once with ammonia B. It is formed only after some time. Absence of baryta, 166 presence of STRONTIA. Mix the remainder of the hydrochloric acid solution with sulphate of potassa, let the mixture stand for some time, then filter, and test the filtrate with ammonia and oxalate of ammonia for LIME. $194. (Examination for Magnesia.) TO A PORTION OF THE FLUID IN WHICH CARBONATE, SULPHATE, AND OXALATE OF AMMONIA HAVE FAILED TO PRODUCE A PRECIPITATE (§ 193, 1 [163]), OR OF THE FLUID FILTERED FROM THE PRECIPITATES FORMED (§ 193, 2 [164]), ADD AMMONIA, THEN SOME PHOSPHATE OF SODA, AND, SHOULD A PRECIPITATE NOT AT ONCE FORM, RUB THE INNER SIDES OF THE VESSEL WITH A GLASS ROD, AND THEN LET THE MIXTURE STAND FOR SOME TIME. 1. NO PRECIPITATE IS FORMED: absence of magnesia. Evapo- 167 rate another portion of the fluid to dryness,* and ignite gently. If a residue remains, treat the remainder of the fluid the same as the sample, and examine the residue, which by the moderate ignition to which it has been subjected has been freed from ammonia, for potassa and soda, according to the directions of § 195.-If no residue is left, this is a proof of the absence of the fixed alkalies; pass on to § 196. 2. A PRECIPITATE IS FORMED: presence of MAGNESIA. As testing 168 for alkalies can proceed with certainty only after the removal of magnesia, evaporate the remainder of the fluid to dryness, and ignite until all ammoniacal salts are removed. Warm the residue with water, add baryta-water, prepared from the crystals, as long as a precipitate continues to form, boil, filter, add to the filtrate a mixture of carbonate of ammonia with some caustic ammonia in slight excess, heat for some time gently, filter, evaporate the filtrate to dryness, adding some chloride of ammonium during the process (to convert into chlorides the caustic alkalies that may have formed), ignite the residue gently, then dissolve it in a little water, precipitate, if necessary, once more, with ammonia and carbonate of ammonia, evaporate again, and if a residue remains, ignite this gently, and finally examine it according to the directions of § 195. $195. (Examination for Potassa and Soda.) YOU HAVE NOW TO EXAMINE FOR POTASSA AND SODA THE GENTLY IGNITED RESIDUE, FREE FROM SALTS OF AMMONIA AND ALKALINE EARTHS, WHICH HAS BEEN OBTAINED IN § 194, 1 (167), OR IN § 194, 2 (168). Dissolve it in a little water, filter, if necessary, evaporate until *The most convenient way is to conduct the evaporation in the cover of a platinum crucible. there is only a small quantity of fluid left, and transfer one half of this to a watch-glass, leaving the other half in the porcelain dish. 1. To the one-half in the porcelain dish add, after cooling, a few 169 drops of solution of bichloride of platinum. If a yellow, crystalline precipitate forms immediately, or after some time, POTASSA is present. Should no precipitate form, evaporate to dryness at a gentle heat, and treat the residue with a very small quantity of water or, if chlorides alone are present, with a mixture of water and alcohol, when the presence of minute traces of potassa will be revealed by a small quantity of a heavy yellow powder being left undissolved. 2. To the other half of the fluid (in the watch-glass) add some 170 antimonate of potassa. If this produces at once or after some time a crystalline precipitate, SODA is present. If the quantity of soda present is only very trifling, it often takes twelve hours before minute crystals of antimonate of soda will separate; you must therefore always wait full that time for the possible manifestation of the reaction, before deciding, from its non-appearance, that no soda is present. As regards the form of the crystals, consult § 91. § 196. (Examination for Ammonia.) There remains still the examination for ammonia. Triturate 171 some of the body under examination, or, if a fluid, a portion of the latter, together with an excess of hydrate of lime, and, if necessary, a little water. If the escaping gas smells of ammonia, if it restores the blue color of reddened litmus paper, and forms white fumes with hydrochloric acid vapors, brought into contact with it by means of a glass rod, AMMONIA is present. The reaction is the most sensitive, if the trituration is made in a small beaker, and the latter covered with a glass plate with a slip of moistened turmeric or moist reddened litmus paper adhering to the under side. Complex Compounds. A, 1. SUBSTANCES SOLUBLE IN WATER. DETECTION OF ACIDS.* I. In the Absence of Organic Acids. § 197. Consider, in the first place, which are the acids that form with the bases found compounds soluble in water, and let this guide you in the examination. To students the table given in Appendix IV. will prove of considerable assistance. 1. The ACIDS of ARSENIC, as well as CARBONIC ACID, HYDROSUL- 172 PHURIC ACID, CHROMIC ACID, and SILICIC ACID, have generally been detected already in the course of testing for the bases; compare also § 181, 1 and 2. * Consult also Section III. 2. Add to a portion of the solution chloride of barium or, if lead, silver, or suboxide of mercury are present, nitrate of baryta, and, should the reaction of the fluid be acid, add ammonia to neutral or slightly alkaline reaction. a. No PRECIPITATE IS FORMED: absence of sulphuric acid, 173 phosphoric acid, chromic acid, silicic acid, oxalic acid, arsenious and arsenic acids, as well as of notable quantities of boracic acid and hydrofluoric acid.* Pass on to 3 (175). b. A PRECIPITATE IS FORMED. Dilute the fluid, and add 174 hydrochloric acid; if the precipitate does not redissolve, or at least not completely, SULPHURIC ACID is present. 3. Add nitrate of silver to a portion of the solution. If this fails 175 to produce a precipitate, test the reaction, and add to the fluid, if it is acid, some dilute ammonia, taking care to add the reagent so gently and cautiously that the two fluids do not intermix; if the reaction is alkaline, on the other hand, add with the same care some dilute nitric acid, instead of ammonia, and watch attentively, whether a precipitate or a cloud forms in the layer between the two fluids. a. NO PRECIPITATE IS FORMED IN THE LAYER BETWEEN THE 176 TWO FLUIDS, NEITHER IMMEDIATELY NOR AFTER SOME TIME. Pass on to 4 (181); there is neither chlorine, bromine, iodine, b. A PRECIPITATE IS FORMED. Observe the colort of it, 177 then add nitric acid, and shake the mixture. a. The precipitate redissolves completely: absence of chlorine, bromine, iodine, cyanogen, ferro- and ferricyanogen, and also of sulphur. Pass on to 4 (181). if B. A residue is left: chlorine, bromine, iodine, cyanogen, 178 ferro- or ferricyanogen may be present; and if the residue is black or blackish, HYDROSULPHURIC ACID or a soluble METALLIC SULPHIDE.-The presence of sulphur may, necessary, be readily established beyond doubt, by mixing another portion of the solution with some solution of sulphate of copper. aa. Test another portion of the fluid for IODINE, and subsequently for BROMINE, by the methods described in $157. bb. Test a small portion of the fluid with sesqui- 179 chloride of iron for FERROCYANOGEN; and, if the color of the silver precipitate leads you to suspect the presence of * If the solution contains an ammoniacal salt in somewhat considerable proportion, the non-formation of a precipitate cannot be considered a conclusive proof of the absence of these acids, since the baryta salts of most of them (not the sulphate), are, in presence of ammoniacal salts, more or less soluble in water. That the cyanogen in cyanide of mercury is not indicated by nitrate of silver has been mentioned § 181, 5 (73). Chloride, bromide, cyanide, and ferrocyanide of silver, and oxalate, silicate, and borate of silver are white; iodide of silver, tribasic phosphate, and arsenite of silver are yellow; arsenate of silver and ferricyanide of silver are brownish-red; chromate of silver is purple-red; sulphide of silver black. FERRICYANOGEN, test another portion for this latter cc. CYANOGEN, if present in form of a simple metallic dd. Should bromine, iodine, cyanogen, ferrocyanogen, 180 ferricyanogen, and sulphur not be present, the precipitate which nitric acid has failed to dissolve, consists of CHLORIDE of silver. However, should the analytical process have revealed the presence of any of the other bodies, a special examination for chlorine may become necessary, viz., in cases where the quantity of the precipitate will not enable the operator to pronounce with positive certainty on the presence or absence of the latter element.* In such cases, which are of rare occurrence, however, the method given in § 157 is resorted to. 4. Test another portion for NITRIC ACID, by means of sulphate of 181 iron and sulphuric acid (§ 159). 5. To ascertain whether CHLORIC ACID is present, pour a little concentrated sulphuric acid over a small sample of the solid body under examination ensuing yellow coloration of the acid resolves the question in the affirmative (§ 160). You have still to test for phosphoric acid, boracic acid, silicic acid, oxalic acid, and chromic acid, as well as for hydrofluoric acid. For the first five acids test only in cases where both chloride of barium and nitrate of silver have produced precipitates in neutral solutions. Compare also foot note to § 197, 2, a. 6. Test for PHOSPHORIC ACID, by adding to a portion of the fluid 182 ammonia in excess, then chloride of ammonium and sulphate of magnesia (§ 143, 7). Very minute quantities of phosphoric acid are detected most readily by means of molybdic acid (§ 143, 11). 7. To effect the detection of OXALIC ACID and HYDROFLUORIC ACID, add chloride of calcium to a portion of the solution. If this produces a precipitate which is not redissolved by addition of acetic acid, one or both bodies are present. Examine therefore now a sample of the original substance for fluorine, according to the directions of § 147, 5, another sample for oxalic acid, by the method given in § 146, 7. 8. Acidulate a portion of the fluid slightly with hydrochloric 183 * Supposing, for instance, the solution of nitrate of silver to have produced a copious precipitate insoluble in nitric acid, and the subsequent examination to have shown mere traces of iodine and bromine, the presence of chlorine may be held to be demonstrated without requiring additional proof. acid, and then test for BORACIC ACID, by means of turmeric paper (§ 145). 9. Should SILICIC ACID not yet have been found in the course of testing for the bases, acidulate a portion of the fluid with hydrochloric acid, evaporate to dryness, and treat the residue with hydrochloric acid (§ 150, 3). 10. CHROMIC ACID is readily recognised by the yellow or red color of the solution, and by the purple-red color of the precipitate produced by nitrate of silver. If there remains the least doubt on the point, test for chromic acid with acetate of lead and acetic acid (§ 138). Complex Compounds. A, 1. SUBSTANCES SOLUBLE IN WATER. DETECTION OF ACIDS. II. In Presence of Organic Acids. $198. 1. The examination for inorganic acids, inclusive of oxalic acid, 184 is made in the manner described in § 197. As the tartrates and citrates of baryta and oxide of silver are insoluble in water, tartaric acid and citric acid can be present only in cases where both chloride of barium and nitrate of silver have produced precipitates in the neutral fluid; still, in drawing a conclusion, you must bear in mind that the said salts are slightly soluble in solutions of salts of ammonia. The examination for the organic acids is conducted as follows :— 2. Make a portion of the fluid feebly alkaline by addition of am- 185 monia, filter, if necessary, add some chloride of ammonium, then chloride of calcium, shake vigorously, and let the mixture stand at rest from ten to twenty minutes. a. No PRECIPITATE IS FORMED, NOT EVEN AFTER THE LAPSE OF SOME TIME. Absence of tartaric acid; pass on to 3. b. A PRECIPITATE IS FORMED IMMEDIATELY, OR AFTER SOME 186 Filter, wash, and keep the filtrate for further examination according to the directions of 3. TIME. Digest and shake the precipitate with solution of soda, without applying heat, then dilute with a little water, filter, and boil the filtrate some time. If a precipitate separates, TARTARIC ACID may be assumed to be present. Filter hot, and subject the precipitate to the ammonia and nitrate of silver test described in § 162, 8. 3. Mix the fluid in which chloride of calcium has failed to produce a precipitate, or that which has been filtered from the precipitate-in which latter case some more chloride of calcium is to be added-with alcohol. a. No PRECIPITATE IS FORMED. malic acid. Pass on to 4. b. A PRECIPITATE IS FORMED. Absence of citric acid and 187 Filter and treat the filtrate 188 as directed in 4. As regards the precipitate, treat this as |