chloric acid and by the subsequent detection of sesquioxide of chromium in the solution. Its presence is confirmed by fusing with carbonate of soda (§ 138). 3. Boil a portion of the substance with nitric acid. a. If nitric acid is evolved, and sulphur separates, this is confirmative of the presence of a metallic SULPHIDE. b. If violet vapors escape, the compound is a metallic IODIDE.* c. If reddish-brown fumes of a chlorine-like smell are evolved, the compound is a metallic BROMIDE,* in which case the fumes will color starch yellow (§ 153). 92 4. Dilute a small portion of the nitric acid solution-or of the 93 filtrate of this solution, should the nitric acid have left an undissolved residue and add nitrate of silver. A white precipitate, which, after washing, is soluble in ammonia, and fuses without decomposition when heated, indicates CHLORINE.* 5. Boil a portion of the substance with hydrochloric acid, filter 94 if necessary, dilute with water, and add chloride of barium. A white precipitate, which does not redissolve even upon addition of a large quantity of water, indicates SULPHURIC ACID. 6. Test for BORACIC ACID as directed § 144, 6. 7. If none of the acids enumerated from 1 to 6 are present, there is reason to suspect the presence of PHOSPHORIC ACID, OXALIC ACID, OF FLUORINE, or the total absence of acids. To the presence of oxalic acid your attention will have been called already in the course of the preliminary examination (8). Phosphoric acid and fluorine have been found already if they were combined with an alkaline earth, and also oxalic acid, if combined with baryta, strontia, or lime, 87 to 89; they need therefore here be tested for only where the examination has revealed the presence of some other base. To that end precipitate the base, if belonging to Group V. or VI., with hydrosulphuric acid, or if belonging to Group IV., with sulphide of ammonium, and filter. If you have precipitated with sulphide of ammonium, add to the filtrate hydrochloric acid to acid reaction, expel in either case the hydrosulphuric acid by boiling, and filter if necessary. Test a portion of this solution for phosphoric acid, oxalic acid, and fluorine, as directed 70. If the base was alumina or sesquioxide of chromium or magnesia, test for phosphoric acid with molybdate of ammonia in the nitric acid solution of the substance (§ 142, 10); for oxalic acid with binoxide of manganese and sulphuric acid (§ 145); for fluorine with sulphuric acid (§ 146). 95 * It i sometimes more convenient, as for instance in the case of subiodide, subbromide and subchloride of mercury, to test for the halogen by boiling the substance with soda, filtering, and testing the filtrate according to 73. Simple Compounds. B. SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLe in Water, BUT SOLUBLE IN ACIDS. Detection of the Acid. II. Detection of Organic Acids. § 187. 1. FORMIC ACID cannot be present, as all the formates are 96 soluble in water. 2. ACETIC ACID has been revealed already in the preliminary examination, by the evolution of acetone. Confirm with sulphuric acid and alcohol (§ 171). 3. BENZOIC ACID is usually detected by its separating on solution of the substance in hydrochloric acid, or when the hydrochloric solution cools. Confirm by washing and drying the precipitate and then subliming it. 4. Boil a portion of the substance for some time with solution of 97 carbonate of soda in excess, and filter hot. You have now, in most cases, the organic acid in solution in combination with soda. Acidulate the solution slightly with hydrochloric acid, expel the carbonic acid by heat, and test as directed § 184. With bases of the fourth group, and also in presence of oxide of lead, this mode of separation is not completely successful. In exceptional cases of the kind add to the filtrate, after boiling with carbonate of soda, sulphide of ammonium until the whole of the metallic oxide is thrown down, filter and proceed as above. Simple Compounds. C. SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WATER, HYDROCHLORIC ACID, NITRIC ACID, AND NITRO-HYDROCHLORIC ACID. Detection of the Base and the Acid. Under this head we have to consider the following substances as 98 the only bodies likely to be met with, viz.-SULPHATE OF BARYTA, SULPHATE OF STRONTIA, SULPHATE OF LIME, FLUORIDE of CALCIUM, SILICA, strongly ignited or native ALUMINA, SULPHATE OF LEAD, compounds of LEAD with CHLORINE and BROMINE; compounds of SILVER with CHLORINE, BROMINE, IODINE, and CYANOGEN; ignited or native BINOXIDE OF TIN, ignited SESQUIOXIDE OF CHROMIUM, and lastly SULPHUR and CARBON. For the simple silicates I refer to § 205, for the ferro- and ferricyanides to § 204. Whether or no these latter compounds are to be suspected, you will have learnt from the preliminary examination. Sulphate of lime and chloride of lead are not altogether insoluble in water, and sulphate of lead may be dissolved in hydrochloric acid. However, as these compounds are so sparingly soluble that complete solution of them is seldom effected, they are included here also to ensure their detection, should they have been overlooked in the examination of the aqueous or acid solution. 1. Free SULPHUR must have been detected already in the preliminary examination. 2. CARBON is generally black; it is insoluble in aqua regia; put on platinum foil, with the blowpipe flame playing upon the under side of the foil, it is consumed;* by deflagration with nitrate of potassa it yields carbonate of potassa. 3. SESQUIOXIDE OF CHROMIUM is green or blackish and green would have been previously detected in the microcosmic bead (18). 4. Pour sulphide of ammonium over a very small quantity of 99 the substance. a. IT TURNS BLACK; this indicates a salt of lead or silver. B. The body evolved cyanogen by ignition in the glass tube and y. The body remained unaltered by ignition in the glass tube: b. IT REMAINS WHITE: absence of a salt of lead or silver. 100 B. Triturate a small portion with finely pulverized quartz, aa. White fumes are evolved, which redden litmus, and render turbid a drop of water (§ 150, 6): indicates FLUORIDE OF CALCIUM. Reduce a portion of the substance to a fine powder, decompose this in a platinum crucible with sulphuric acid, and try the reaction on glass (§ 146), to confirm the presence of FLUORINE; boil the residue with hydrochloric acid, filter, neutralize the filtrate with ammonia, and test for LIME with oxalate of ammonia. bb. No fumes are evolved which redden litmus, and render turbid a drop of water. Mix a portion of the very finely pulverized substance with 4 times the quantity of pure carbonate of soda and potassa, and fuse in a platinum * Graphite requires strong heating in a current of oxygen. crucible (or on platinum foil). Boil the fused mass with If the SILICIC ACID was present in the pure state, the mass resulting from the fusion with carbonate of soda and potassa must have dissolved in water to a clear fluid; but if silicates also happened to be present, the bases of them are left behind undissolved, and may be further examined. In the absence of alumina you cannot expect the fusion to dissolve completely in water unless you have employed a large quantity of the flux and a high temperature. If sulphuric acid has been found, the alkaline earth which was combined with it is found on the filter as a carbonate. Wash this, then dissolve in dilute hydrochloric acid, evaporate to dryness, take up with water, and test for BARYTA, STRONTIA, and LIME, as directed 62. Complex Compounds.* A. SUBSTANCES SOLUBLE IN WATER, AND ALSO SUCH AS ARE Detection of the Bases.† (Treatment with Hydrochloric Acid: Detection of Silver, Suboxide The systematic course for the detection of the bases is essen- 101 tially the same for bodies soluble in water, as for those which are soluble only in acids. Where the different nature of the original solution occasions a variation in the course of analysis, such variation will be distinctly stated. I. SOLUTION IN WATER. MIX THE PORTION INTENDED FOR THE DETECTION OF THE 102 BASES WITH SOME HYDROCHLORIC ACID. * I use this term to designate compounds in which all the more frequently occurring bases, acids, metals, and metalloids are supposed to be present. + Consult the explanations in the Third Section, with the contents of which you should make yourself thoroughly acquainted before proceeding further. Regard is here had also to the presence of the acids of arsenic, and of those salts of the alkaline earths which dissolve in hydrochloric acid, and separate again from that solution unaltered upon neutralization of the acid by ammonia. + Consult the remarks in the Third Section. 1. THE SOLUTION HAD AN ACID OR NEUTRAL REACTION PREVIOUSLY TO THE ADDITION OF THE HYDROCHLORIC ACID. a. No PRECIPITATE IS FORMED: this indicates the absence of silver and suboxide of mercury. Pass on to § 190. b. A PRECIPITATE IS FORMED. Add more hydrochloric acid, drop by drop, until the precipitate ceases to increase; then add about six or eight drops more of hydrochloric acid, shake the mixture and filter. The precipitate produced by hydrochloric acid may consist of chloride of silver, subchloride of mercury, chloride of lead, a basic salt of antimony, basic chloride of bismuth, metachloride of tin, possibly also benzoic acid. The basic salt of antimony and the basic chloride of bismuth, however, redissolve in the excess of hydrochloric acid; consequently, if the instructions given have been strictly followed, the precipitate collected upon the filter can consist only of chloride of silver, subchloride of mercury, or chloride of lead (possibly also of the very rare metachloride of tin and benzoic acid, which, however, are disregarded here). Wash the precipitate collected upon the filter twice with Treat the twice-washed precipitate on the filter as follows: 103 B. If there is a residue remaining on the filter, treat it 7. Add to the ammoniacal fluid running off in 8 nitric acid to strongly acid reaction. The formation of a white, curdy precipitate indicates the presence of SILVER.* (If the precipitate still contained lead, the ammoniacal solution generally appears turbid, owing to the separation of a basic salt of lead. This, however, does not interfere with the testing for silver, since the basic salt of lead redissolves upon the addition of nitric acid.) 2. THE ORIGINAL AQUEOUS SOLUTION HAD AN ALKALINE 104 REACTION. a. THE ADDITION OF HYDROCHLORIC ACID TO STRONGLY ACID REACTION FAILS TO PRODUCE EVOLUTION OF GAS OR A *If the quantity of silver is only very small, its presence is indicated by opalescence of the fluid, |