RULE III.—Acidify a third portion with HCl and add BaCl. A white precipitate indicates Sulphates.

RULE IV. To a fourth portion add CaCl..

A white precipitate soluble in excess of H2O indicates Sulphates; if insoluble in excess of H2O or HC2HO2, Oxalates are indicated. A white precipitate, soluble in KOH and reprecipitated upon boiling, indicates Tartrates; the latter test should be confirmed by forming a mirror of silver on the test-tube. A white precipitate, soluble in NH4Cl and reprecipitated upon boiling, indicates Citrates.

For further instruction regarding the separation of these acids consult the chart on page 876.

When Sulphates are present it is important to remove them before attempting the detection of Oxalates, Tartrates, and Citrates by the use of CaCl. To accomplish this, treat the solution with HCl and BaCl2, filter off the BaSO,, neutralize the filtrate with NaOH, and proceed according to the chart on page 876.

RULE V.—Acidify a fifth portion with HNO, and add AgNO, until the precipitation is completed.

Collect the precipitate, wash it, and pour upon the filter NHOH. Acidify the filtrate so obtained with HNO,; a white precipitate indicates Chlorides. When Cyanides are present they must be removed by boiling with HNO, before adding the AgNO3.

RULE VI.—Add to a sixth portion of the solution starch paste and chlorine water.

A blue color indicates Iodides. Continue the addition of chlorine water until the blue color of starch iodide is discharged, then shake with chloroform. A yellowish-red color is imparted to this solvent if Bromides are present.

For fuller directions, see page 862.

RULE VII.—Add a few drops of the solution to a relatively large quantity of (NH)M0O and warm.

Phosphates and Arsenates produce yellow precipitates. The presence or absence of As is always ascertained in the detection of bases. When present, it should be separated from another portion of the solution by HCl and H,S; the filtrate, after boiling to expel HS, is then neutralized with NH2OH and

treated with magnesia mixture. A white crystalline precipitate confirms the presence of Phosphates.

The detection of Pyrophosphates and Metaphosphates may be conducted by the directions given on page 871.

RULE VIII. To an eighth portion apply the special test with H2SO, and FeSO, for Nitrates.

A dark layer at the line of contact reveals their presence.

RULE IX. To some of the dry salt, or to the residue obtained by evaporating a portion of the solution to dryness, add a few drops of strong H2SO, and 15 or 20 drops of alcohol, mix well, and apply flame. Borates, if present, will impart a green color to the flame of the burning alcohol.

Chromates, Manganates, and Permanganates, when present, impart color to the solution. The metals from which their acid radicals arise will be ascertained in the detection of bases. The characters of these salts have been previously discussed under different reactions, which may be employed to more fully establish the presence of their constituent acids.

DIVISION II. When the solution is acid to litmus paper, or when the substance to be analyzed is a solid which requires the use of acid to dissolve it.

After determining the bases by the chart on page 859 (bearing in mind the exception in regard to phosphates) a portion of the material is tested according to Rules I and II, DIVISION I.

A second portion of the solution is then to be treated as follows:

Boil with sufficient solution of Na2CO3 to make the mixture alkaline.

Ppt. consists of the Filt. contains the acids in the form of salts of Na.

carbonates, hydrates, and oxides of the bases

present, and is disregarded.

Divide into two portions.

To one portion add HC1
until slightly acid, boil
to remove CO2, neutral-
ize with NaOH, and test
according to Rules III,
IV, VI, VIII, and IX,
DIVISION I.

To another portion add HNO3 until slightly acid, boil to remove CO2, neutralize with NaOH, and test according to Rules V and VII, and if necessary III, IV, VI, and IX, DIVISION I.

When heavy metals are present Rule I, Division I, is preferably applied to the filtrate after boiling with Na,CO,; the portion

neutralized with HCl and NaOH is recommended for use in all such cases. Rule II should be invariably performed on the original solution or solid. When Cu is present it is best to add, along with the Na,CO,, some NaOH to insure the complete precipitation of that base.

HYDRATES AND OXIDES.

When, in the analysis of an inorganic substance for acids, negative results are obtained, the material under consideration may be either a hydrate or an oxide.

The hydrates of K, Na, Li, Ca, Sr, and Ba are soluble in water, and yield solutions which change red litmus paper blue. The hydrates of other metals are insoluble in water. These, as also the hydrates of Ca, Sr, and Ba, when heated in a dry testtube, give off vapor of water which condenses on the cooler part of the tube; it is characterized by having no odor or taste, and by not changing the color of litmus paper.

Oxides do not yield water when thus heated. The oxides of K, Na, Li, Ca, Sr, and Ba dissolve in water to form hydrates; the oxides of other metals are insoluble in water.

DIVISION III. When the substance is not entirely dissolved by H2O, HCl, or a mixture of HCl and HNO3.

Add water and filter; the filtrate, if it contain solid matter (determined by evaporating a small quantity to dryness), is examined for bases by the chart on page 859, and for acids by Division I. The residue, after treatment with water, is treated with HCl, or, if necessary, with a mixture of HCl and HNO3. Any bases that may be dissolved are detected by the chart on page 859, while the acids are determined according to Division II. The insoluble residue consists of one or more of the following substances: Sulphates of Ba, Sr, Ca, Pb; Chlorides, Bromides, and Iodides of Ag, Pb; certain Oxides which have been highly heated, as FeО, AlО, CÃO, SnO; Silica and Silicates; Carbon and Sulphur (the last two are readily detected in the preliminary examination by heat). This residue is mixed with about four times its weight of dry Na,CO3, and fused on a platinum foil; the mass is boiled with water, and the soluble portion examined for acids according to Division II. The portion undissolved by water is treated with HC1; the solution so obtained evaporated to dryness, the residue dissolved in water with the aid of a little HCl, and examined for bases by the chart on

page 859. Special attention should be given to the notes preceding this chart. If, after fusing with Na,CO,, the metals lead and silver are present in the residue insoluble in water and HCl, they can best be determined by dissolving such portions in HNO, and proceeding with the analysis as directed in Division II. Many of these insoluble substances are detected in a preliminary examination by the use of the blowpipe, as explained in the reactions given under the individual elements.

THE ANALYSIS OF ALLOYS.

The following general outline suffices for the examination of the more common alloys :

Pour over the substance HNO3, sp. gr. 1.20, and evaporate to dryness with a moderate heat. This treatment converts most of the metals into nitrates, which are soluble in water or very weak HNO3; Sb and Sn are, however, changed to oxides, which are insoluble in water or HNO,, while Pt and Au remain unaltered in the metallic state, and hence fail to dissolve in the same liquids.

The residue obtained upon evaporating to dryness is treated with water containing a small amount of HNO, to insure the solution of bismuth; the mixture is then filtered, and the analysis of the filtrate conducted according to the chart on page 859. The oxides of Sb and Sn may be separated from the metallic Pt and Au by warming with strong HC1; after filtration the Sb and Sn are separated by the chart on page 847.

Pt and Au may be identified by dissolving in a mixture of HC1 and HNO,, and applying the tests given in the chart on page 847.

SECTION II

QUANTITATIVE ANALYSIS.

CHAPTER I.

GRAVIMETRIC PROCESSES.

IN the following short course in gravimetric operations a few typical salts are given for estimation, with the belief that a thorough knowledge of the operations involved in these will enable the learner to carry out most of the processes he will be called on to perform in inorganic work.

Before undertaking this section the student should be thoroughly familiar with the preceding qualitative operations, and it is especially desirable at this point that he should have instruction from some one familiar with the use of analytical balances and weights. In addition, the following rules should be kept constantly in mind by those using a fine balance:

1. Never put any chemical substance directly on the pan of a balance, but first weigh a clean, dry crucible or watch crystal, and then weigh the substance in it.

2. Never put on or take off a weight, or anything else, from a balance when the beam is resting on the knife-edges.

3. All weights should be transferred in regular order, and the forceps always used instead of the fingers.

4. Volatile acids, and all other corrosive substances, like chlorine water, iodine, or solution of ammonia, should be weighed in stoppered weighing-tubes or small test-tubes with closely fitting corks.

5. The door of the balance should be kept open no longer than is absolutely necessary.

In addition to the above rules, it may be said that most substances and containers, that are heated previous to weighing, should be cooled in a desiccator.