PART II.

SYSTEMATIC COURSE

OF

QUALITATIVE CHEMICAL ANALYSIS.

PRELIMINARY REMARKS

ON THE

COURSE OF QUALITATIVE ANALYSIS IN GENERAL, AND ON THE PLAN OF THIS PART OF THE PRESENT WORK IN PARTICULAR.

But

THE knowledge of reagents and of the deportment of bodies with them enables us to ascertain at once whether a simple compound of which the physical properties permit an inference as to its nature, is in reality what we suspect it to be. Thus, for instance, a few simple reactions suffice to show that a body which appears to be calcareous spar is really carbonate of lime, and that another which we hold to be gypsum is actually sulphate of lime. This knowledge usually suffices also to ascertain whether a certain body is present or not in a mixture; for instance, whether or not a white powder contains subchloride of mercury. if our design is to ascertain the chemical nature of a substance entirely unknown to us—if we wish to discover all the constituents of a mixture or chemical compound-if we intend to prove that, besides certain bodies which we have detected, no other substance can possibly be present--if consequently a complete qualitative analysis is our object, the mere knowledge of the reagents, and of the reactions of bodies with them, will not suffice for the attainment of this end; this requires the additional knowledge of a systematic course of analysis, in other words, the knowledge of the order in which solvents, and general and special reagents should be applied, both to effect the speedy and certain detection of every element present, and to prove with certainty the absence of all others. If we do not possess the knowledge of this systematic course, or if, in the hope of attaining our object more rapidly, we adhere to no method, analyzing becomes (at least in the hands of a novice) mere guess-work, and the results obtained are no longer the fruits of scientific calculation, but mere matters of accident, which sometimes may prove lucky hits, and at others total failures.

Every analytical investigation must therefore be based upon a definite method. But it is not by any means necessary that this method should be the same in all cases. Practice, reflection, and a

due attention to circumstances will, on the contrary, generally lead to the adoption of different methods for different cases. However, all analytical methods agree in this, that the substances to be looked for are in the first place classed into groups, which are then again subdivided, until the individual detection of the various substances present is finally accomplished. The diversity of analytical methods depends partly on the order in which reagents are applied, and partly on their selection.

Before we can venture upon inventing methods of our own for individual cases, we must first make ourselves thoroughly conversant with a course of chemical analysis in general. This system must have passed through the ordeal of experience, and must be adapted to every imaginable case, so that afterwards, when we have acquired some practice in analysis, we may be able to determine which modification of the general method will be best adapted to a given case.

The exposition of such a systematic course, adapted to all cases, tested by experience, and combining simplicity with the greatest possible security, is the object of the First Section.

The elements and compounds comprised in it are the same which we have studied in Part I., with the exception of those discussed more briefly, and marked by the use of smaller type.

The subdivisions of this systematic course are, 1, Preliminary Examination; 2, Solution; 3, Actual Examination.

The third subdivision (the Actual Examination) is again divided into (1) Examination of compounds in which but one base and one acid are assumed to be present: and (2) Examination of mixtures or compounds in which all the substances treated in the present work are assumed to be present. With respect to the latter I have to remark that where the preliminary examination has not clearly demonstrated the absence of certain groups of substances, the student cannot safely disregard any of the paragraphs to which reference is made in consequence of the reactions observed. In cases where the intention is simply to test a mixture for certain substances, and not to ascertain all its constituents, it will be easy to select the particular numbers which ought to be attended to.

As the construction of a universally applicable systematic course of analysis requires due provision for every contingency that may possibly arise, it is self-evident that, though in the system here laid down the various bodies comprised in it have been assumed to be mixed up together in every conceivable way, it was absolutely indispensable to assume that no foreign organic matters were present, since the presence of such matters would introduce various complications.

Although the general analytical course laid down here is devised and arranged in a manner to suit all possible contingencies, still there are special cases in which it may be advisable to modify it. A preliminary treatment of the substance is also sometimes necessary, before the actual analysis can be proceeded with; the presence of coloring or slimy organic matters more especially requires certain preliminary operations. The Second Section will be found to contain a detailed description of the special methods employed to meet certain cases which frequently occur. Some of these methods show how the analytical process becomes simplified as the number of substances decreases to which regard must be had.

In conclusion, as an intelligent and successful pursuit of analysis is possible only with an accurate knowledge of the principles whereon the detection and separation of bodies depend, I have given in the Third Section an explanation of the general analytical process, with numerous additions to the practical operations. As this third section may properly be regarded as the key to the first and second sections, I strongly recommend students to make themselves early and thoroughly acquainted with it. I have devoted a special section to this theoretical explanation, as I think it will be understood better in a connected form than it would have been by explanatory additions to the several paragraphs, which, moreover, might have materially interfered with the perspicuity of the practical process.

I have also in this third section taken occasion to point out in what residues, solutions, precipitates, &c., which are obtained in the systematic course of analysis, the more rarely occurring elements may be expected to be met with; and also to give instructions how to proceed with a view to ensure the detection of these bodies also systematically.

SECTION I.

PRACTICAL PROCESS FOR THE ANALYSIS OF COMPOUNDS AND MIXTURES IN GENERAL.

I. PRELIMINARY EXAMINATION.*

§ 175.

EXAMINE, in the first place, the external properties, such as the 1t color, shape, hardness, gravity, odor, &c., of the substance, since these will often enable you in some measure to infer its nature. Before proceeding, if the quantity of the substance is limited, you must consider how much may safely be spared for the preliminary examination. A reasonable economy is in all cases advisable, even though you may possess the substance in large quantities; but, under all circumstances, let it be a fixed rule never to use up the whole of what you possess of a substance, but always to keep a portion of it for unforeseen contingencies, and for confirmatory experiments.

A. THE BODY UNDER EXAMINATION IS SOLID.

I. IT IS NEITHER A METAL NOR AN ALLOY.

$176.

1. The substance is fit for examination if in powder or in minute 2 crystals; but in the case of larger crystals or solid pieces, a portion must, if practicable, be first reduced to fine powder. Bodies of the softer kind may be triturated in a porcelain mortar; those of a harder

* Consult also the observations in the Third Section of Part II.
+ These marginal numbers are simply intended to facilitate reference.

nature must first be broken into small pieces in a steel mortar; or upon a steel anvil, and the pieces then be triturated in an agate

mortar.

2. PUT SOME OF THE POWDER INTO A GLASS TUBE, SEALED 3 AT ONE END, ABOUT SIX CENTIMETRES LONG AND FIVE MILLIMETRES WIDE, AND HEAT first gently over the spirit or gas-lamp, then intensely in the blowpipe flame. The reactions resulting may lead to many positive or probable conclusions regarding the nature of the substance. The following are the most important of these reactions, to which particular attention ought to be paid; it often occurs that several of them are observed in the case of one and the same substance.

a. THE SUBSTANCE REMAINS UNALTERED: absence of 4 organic matters, salts containing water of crystallization, readily fusible matters, and volatile bodies (except carbonic acid, which often escapes without visible change).

b. THE SUBSTANCE DOES NOT FUSE AT A MODERATE HEAT 5 BUT SIMPLY CHANGES COLOR. From white to yellow, turning white again on cooling, indicates OXIDE OF ZINC; from white to yellowish brown, turning to a dirty light yellow on cooling, indicates BINOXIDE OF TIN; from white or yellowishred to brownish-red, turning to yellow on cooling, the body fusing at a red heat, indicates OXIDE OF LEAD; from white, or pale yellow, to orange yellow, up to reddish-brown, turning pale yellow on cooling, the body fusing at an intense red heat, indicates TEROXIDE OF BISMUTH; from brownish-red to black, turning brownish-red again on cooling, indicates SESQUIOXIDE OF IRON; from yellow to dark orange, the body fusing at an intense heat, indicates NEUTRAL CHROMATE OF POTASSA, &c. C. THE SUBSTANCE FUSES WITHOUT EXPULSION OF 6 AQUEOUS VAPORS. If by intense heating, gas (oxygen) is evolved, and a small fragment of charcoal thrown in is energetically consumed, NITRATES or CHLORATES are indicated.

d. AQUEOUS VAPORS ARE EXPELLED, WHICH CONDENSE IN THE COLDER PART OF THE TUBE: this indicates either (a) SUBSTANCES CONTAINING WATER OF CRYSTALLIZATION, in which case they will generally readily fuse, and re-solidify after expulsion of the water; many of these swell considerably whilst yielding up their water, e.g., borax, alum; or (8) decomposable HYDRATES, in which case the bodies often will not fuse; or (y) anhydrous salts, holding WATER MECHANICALLY ENCLOSED between their lamellæ, in which case the bodies will decrepitate; or (8) bodies with MOISTURE externally adhering to them.

Test the reaction of the condensed fluid in the tube; if it is alkaline, ammonia is indicated; if acid, a volatile acid (sulphuric, sulphurous, hydrofluoric, hydrochloric, hydrobromic, hydriodic, nitric, &c.).

7

e. GASES OR FUMES ESCAPE. Observe whether they have a 8 color, a smell, an acid or alkaline reaction, whether they are inflammable, &c.

aa. OXYGEN indicates peroxides, chlorates, nitrates, &c. A glimmering slip of wood is relighted in the gaseous current.

bb. SULPHUROUS ACID is often produced by the decomposition of sulphates; it may be known by its odor and by its acid reaction.

cc. HYPONITRIC ACID, resulting from the decomposition of nitrates, especially those of the heavy metals; it may be known by the brownish-red color and the odor of the fumes.

dd. CARBONIC ACID indicates carbonates decomposable by heat, or oxalates of reducible metals. The gas is colorless and tasteless, non-inflammable; a drop of lime-water on watch-glass becomes turbid on exposure to the gaseous

current.

ee. CARBONIC OXIDE indicates oxalates and also formates. The gas burns with a blue flame. In the case of oxalates the carbonic oxide is generally mixed with carbonic acid, and is therefore more difficult to kindle: in the case of formates there is marked carbonization. Oxalates evolve carbonic acid when brought into contact with binoxide of manganese, a little water, and some concentrated sulphuric acid, on a watchglass; formates evolve no carbonic acid under similar cir

cumstances.

ff. CHLORINE, BROMINE, OR IODINE indicate decomposable chlorides, bromides, or iodides. The gases are readily recognised by their color and odor. Iodine, if evolved in any quantity, forms a black sublimate (compare 9).

99. CYANOGEN indicates cyanides decomposable by heat, The gas may be known by its odor, and, when tolerably pure, by the crimson flame with which it burns.

hh. HYDROSULPHURIC ACID indicates sulphides containing water; the gas may be readily known by its odor.

. AMMONIA, resulting from the decomposition of ammoniacal salts, or also of cyanides of nitrogenous organic matters, in which latter cases browning or carbonization takes place, and either cyanogen or offensive empyreumatic oils escape with the ammonia.

f. A SUBLIMATE FORMS. This indicates volatile bodies: 9 the following are those more frequently met with :—

aa. SULPHUR. Eliminated from mixtures or from many of the metallic sulphides. Sublimes in reddish-brown drops, which solidify on cooling, and turn yellow or yellowishbrown.

bb. IODINE. Eliminated from mixtures, many iodides, iodic acid, &c. Violet vapor, black sublimate, smell of iodine.

cc. AMMONIA SALTS give white sublimates; heated with carbonate of soda and a drop of water on platinum foil they evolve ammonia.

dd. MERCURY and its compounds. METALLIC MERCURY forms globules; SULPHIDE OF MERCURY is black, but acquires a red tint when rubbed; CHLORIDE OF MERCURY fuses before volatilizing; SUBCHLORIDE OF MERCURY sublimes without previous fusion, the sublimate, which is yellow whilst hot, turns white on cooling. The red IODIDE OF MERCURY

gives a yellow sublimate.

ee. ARSENIC and its compounds.

METALLIC ARSENIC