TABLE FOR GROUP III.

The precipitate produced by hydrate of ammonium may be Ur HO, Fe,H,O,, Cr,H,O,, or ALHO,; it may also be a phosphate or fluoride of Ba, Sr, Ca, or Mg, or a phosphate of Ur, Fe, Cr, or Al. The oxalates will have been destroyed by ignition; and the borates do not occur.

It will be sufficient to ascertain the presence of the phosphoric radical by dissolving a small portion of the precipitate in the least possible quantity of dilute HNO in a watch-glass, adding a trace of NH HO, to neutralize as far as possible the excess of HNO, without reprecipitating the salt dissolved, and then introducing a few drops of AgNO, the presence of H,PO, is ascertained by the immediate precipitate of the yellow Ag, PO

The mass of the precipitate is then treated with sesquicarbonate of ammonium in the cold: complete solution indicates

the presence of Ur,H,O,. Evaporate to dryness; dissolve the yellow residue in HA, and add K,Cfy: a brownish red precipitate or colour indicates Ur.

If a residue is left, it is to be examined for Fe, Cr, or Al.

Boil for five minutes with H,O, to separate Ba Sr, and Ca as oxalates; filter, allow to cool, and add excess of KHO.

TABLE FOR GROUP III. a.

The precipitate produced by sulphide of ammonium may be Zn,S, Mn S, Ni,S, or Co,S.

Dissolve it in concentrated HCl, adding one or two drops of concentrated HNO, when boiling. To the solution add excess of KHO. Perfect solution indicates

the presence of Zn,S: add HS to the solution, a white precipitate of ZnS indicates Zn.

A precipitate of a flesh colour consists of Mn,S; a black precipitate, of NiS or Co,S.

Dissolve in concentrated HCl, add excess of KĀ, and pass HS gas: the non-formation of a precipitate indicates

the presence of Mn,S. Confirm by the addition of NH HO, which will form NH,HS, and give a fleshcoloured or buff precipitate of Mn,S, indicating Mn.

The occurrence of a precipitate proves the existence of Ni,S, or Co,S.

Dissolve in concentrated HCl; add one drop of concentrated HNO, when boiling, then KCy in excess. Boil the solution, and acidify with dilute HCI: a precipitate indicates

the presence of
nickel, which must
be confirmed by
fusion with borax:
a red-brown bead
indicates
Ni.

TABLE FOR GROUP IV.

The absence of a pre-
cipitate indicates
cobalt, the presence
of which must be
confirmed by eva-
porating the solution
to dryness, and
fusing a portion of
the residue with
borax: a blue bead
indicates
Co.

The precipitate produced by carbonate of ammonium, in the presence of NH HO and NH, Cl, may be Ba, CO, Sr., SO,, or CaCO3.

Dissolve in the smallest quantity of dilute HCI, add KCrO, in solution: the formation of a precipitate, after the lapse of a few minutes, indicates

the presence of Ba.

The absence of any precipitate indicates the presence of strontium or calcium.

Divide the solution into two parts, dilute it with a small quantity of water.

1.

Add a saturated solution of
CaSO: a precipitate, after
standing fifteen minutes,
indicates
Sr.

2.

If no precipitate occurs in 1.
after fifteen minutes standing,
add to 2. (NH),Ō: a white
precipitate indicates
Ca.

TABLE FOR GROUP V.

If the various group-tests have produced no precipitate in the solution under examination, either NH, Mg, K, or Na is present. Of these basic ! radicals, NH, will have been already detected in the preliminary examination (p. 391).

Divide the solution into two portions, one being thrice the bulk of the other.

Having now considered the method of detecting the basic radical in a simple salt, we proceed to give the details of—

SECTION II.-The examination for the acid constituent. The student must have already perceived that, although compound basic radicals are extremely rare, the compound acidradicals which occur in the course of analysis are very numerous. The latter bodies, though easily detected if they yield characteristic products of decomposition, are, however, in many cases recognized with great difficulty, particularly when of very great complexity. The recognition of the basic radicals by means of the blowpipe is comparatively easy, because in the majority of cases the acid-radical of the salt is expelled, or its basic constituent is left in combination with oxygen only as an oxide, the characters of which are easily recognized; but when we wish to detect the acid-radical present by the same means, the ready decomposability of the latter forms an insuperable obstacle.

We have, however, at our disposal a method of Preliminary Examination which is of the greatest service in enabling us to form an idea concerning the nature of the acid-radical present, and occasionally, indeed, affording us decisive proof of its exist

EXAMINATION FOR THE ACID CONSTITUENT.

403

ence. One of the reactions thus employed consists in the decomposing influence which concentrated sulphuric acid exerts upon almost all saline combinations. The sulphuric radical unites with the basic constituent of the salt to form a sulphate, while the acid-radical in the substance either unites with the hydrogen to form a new acid which is liberated, or else splits up into characteristic products of decomposition. Whichever result takes place, its occurrence generally affords sufficient evidence of the nature of the acid constituent originally present.

In addition to the experiment with concentrated sulphuric acid, decisive information concerning the nature of the acidradical present in the substance under examination may often be obtained by gently warming the substance, or its solution, with dilute hydrochloric acid. All concentrated acids, particularly concentrated nitric and hydrochloric, when heated, themselves evolve pungent vapours, which mask the otherwise characteristic odour of the newly liberated acid.

In observing the action of sulphuric or hydrochloric acid upon a salt, it must be borne in mind that the nature of the basic radical present greatly influences the reaction. Thus the salts containing basic radicals of the first and second subdivisions united with weak acid-radicals, or with acid-radicals the hydrogen salts of which are gaseous at ordinary temperatures, are much more readily decomposed by strong acids than are the salts of other subdivisions.

To take an example of this difference in the behaviour of salts. NaCl or BaCl is instantly decomposed by the addition of H, SO,, the HCl escaping with effervescence,-while AgCl is not acted upon. K, S or Ca, S is decomposed in a similarly rapid manner by HCl even when dilute, while Fe, S is but slowly acted upon, and Pb, S remains wholly intact. The varying solubility of the different compounds doubtless here influences the play of affinities. Carbonates and sulphites, the acids of which split, as soon as liberated, into water and carbonic and sulphurous anhydrides, are decomposed, perhaps without exception, even by weak acids, whatever may be the solubility of the individual salt operated on; but here it is obvious that the decidedly gaseous character of the chief product of the action must exert a powerful influence in determining the decomposition.

Preliminary examination for the detection of the acid-radical.

1. Effervescence in the cold, 1. Presence of МСТО,

Many acid-radicals being by no means distinctly recognized by analysis in the wet way, it will be well for the student to follow