with chloride of ammonium in excess. The part of the precipitate insoluble in solution of soda is examined for CHROMIUM, by fusion with nitrate of potassa and carbonate of soda (§ 102, 8).

bb. Mix the solution first with a few drops of hydrochloric acid, boil to expel the whole of the carbonic acid, then add some ammonia and sulphide of ammonium.

aa. No precipitate forms: absence of manganese 158 and zinc. Mix the solution containing chloride of barium with dilute sulphuric acid in slight excess, boil, filter, supersaturate with ammonia, and mix with oxalate of ammonia. If a precipitate of oxalate of LIME forms, filter, and test the filtrate with phosphate of soda for magnesia.

if

BB. A precipitate forms. Filter, and proceed with 159 the filtrate according to the directions of (158). The precipitate may consist of sulphide of manganese and sulphide of zinc, and may contain traces also of sulphide of cobalt and sulphide of nickel. Wash it with water containing some sulphide of ammonium, then treat with acetic acid, which will dissolve the sulphide of MANGANESE, any is present, leaving the other sulphides undissolved. Filter, boil the filtrate with solution of soda, and test the precipitate, which may form, with carbonate of soda in the outer blowpipe flame for MANGANESE. Free the residuary part of the precipitate which acetic acid has failed to dissolve, by washing, from the acetic acid solution still adhering to it, and then treat it with dilute hydrochloric acid, which will dissolve the zinc, if any is present. Filter, add some nitric acid to the filtrate, and concentrate the mixture considerably by boiling; then add to it concentrated solution of soda in excess, boil, filter if necessary, and test the filtrate with sulphide of ammonium for ZINC. Should a precipitate insoluble in solution of soda remain in the last operation, or should the dilute hydrochloric acid have left a black residue, test this precipitate and residue for COBALT and NICKEL, if you have not already previously detected the presence of these bodies; compare (148 and 149). γ. If you have found alkaline earths in a and ẞ, and 160 wish to know the acids in combination with which they have passed into the precipitate produced by sulphide of ammonium, this may be ascertained by making the following experiments with the remainder of the hydrochloric acid solution.

aa. Evaporate a small portion in a small dish or on a 161 watch-glass on the water-bath, dry the residue thoroughly, then treat with hydrochloric acid. If there was any SILICIC ACID in the solution, this will be left undissolved. Test the solution now for PHOSPHORIC ACID, by means of molybdic acid (§ 142, 10).

bb. Mix another portion with carbonate of soda in excess, boil for some time, filter, and test one-half of the filtrate for OXALIC ACID, by acidifying with acetic acid and adding solution

of sulphate of lime; the other half for BORACIC ACID, by slightly acidifying with hydrochloric acid, and testing with turmeric-paper (§ 144 and § 145.)

cc. Precipitate the remainder with ammonia, filter, 162 wash and dry the precipitate, and examine it for FLUORINE according to § 146, 5.

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(Separation and Detection of the Oxides of Group II. which are precipitated by Carbonate of Ammonia in Presence of Chloride of Ammonium, viz., Baryta, Strontia, Lime).

To A SMALL PORTION OF THE FLUID IN WHICH AMMONIA AND SULPHIDE OF AMMONIUM HAVE FAILED TO PRODUCE A PRECIPITate (135),

OR OF THE FLUID FILTERED FROM THE PRECIPITATE FORMED, ADD CHLO-
RIDE OF AMMONIUM, IF THE SOLUTION CONTAINS NO AMMONIACAL SALT,
THEN CARBONATE OF AMMONIA AND SOME CAUSTIC AMMONIA, AND
HEAT FOR SOME TIME VERY GENTLY (not to boiling).

1. NO PRECIPITATE FORMS: absence of any notable quantity of 163 baryta, strontia, and lime. Traces of these alkaline earths may, however, be present: to detect them, add to another portion of the fluid some sulphate of ammonia (prepared by supersaturating dilute sulphuric acid with ammonia): if the fluid becomes turbid, it contains traces of BARYTA; add to a third portion some oxalate of ammonia; if the fluid turns turbid - which reaction may perhaps require some time to manifest itself-traces of lime are present. Treat the remainder of the fluid as directed § 196, after having previously removed the traces of lime and baryta which may have been found, by means of the reagents that have served to effect their detection.

2. A PRECIPITATE IS FORMED. Presence of LIME, BARYTA, or 164 STRONTIA. Treat the whole fluid of which a portion has been tested with ammonia, and carbonate of ammonia, the same as the sample, filter off the precipitate formed, after gently heating, as directed above, and test portions of the filtrate with sulphate and oxalate of ammonia for traces of lime and baryta, which it may possibly still contain; remove such traces, should they be found, by means of the said reagents, and examine the fluid, thus perfectly freed from baryta, strontia, and lime, for magnesia according to the directions of § 196. Wash the precipitate produced by carbonate of ammonia, dissolve it in the least possible amount of dilute hydrochloric acid, and add to a small portion of the fluid a sufficient quantity of solution of sulphate of lime.

a. No precipitate is formed, NOT EVEN AFTER THE LAPSE OF SOME TIME. Absence of baryta and strontia; presence of LIME. To remove all doubt, mix another sample with oxalate of ammonia.

165

b. A precipitate is formed by solution of sulphate of lime.
a. It is formed immediately; this indicates BARYTA.
Besides this, strontia and lime may also be present.
Evaporate the remainder of the hydrochloric acid solu-
tion of the precipitate produced by carbonate of ammonia to
dryness, digest the residue with strong alcohol, decant the fluid
from the undissolved chloride of barium, dilute with an equal
volume of water, mix with a few drops of hydrofluosilicic acid—

which will throw down the small portion of baryta that had dissolved in form of chloride of barium-allow the mixture to stand for some time; filter, and mix the filtrate with dilute sulphuric acid. The formation of a precipitate indicates the presence of strontia or lime, or of both. Filter after some time, wash the precipitate with weak spirit of wine, boil with solution of carbonate of soda, to convert the sulphates into carbonates, filter these off, wash, dissolve in hydrochloric acid, evaporate the solution to dryness, dissolve the residue in water, and test a portion of the solution with dilute solution of sulphate of potassa (§ 96, 3). If a precipitate forms immediately, or in the course of half an hour, the presence of STRONTIA is demonstrated. In that case let the fluid with the precipitate in it stand at rest for some time, then filter, and add ammonia and oxalate of ammonia to the filtrate. The formation of a white precipitate indicates LIME. If sulphate of potassa has failed to produce a precipitate, the remainder of the solution of the residue left upon evaporation is tested at once with ammonia and oxalate of ammonia for lime.

B. It is formed only after some time. Absence of baryta, 166 presence of STRONTIA. Mix the remainder of the hydro

chloric 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.

§ 196.

(Examination for Magnesia.)

TO A PORTION OF THE FLUID IN WHICH CARBONATE, SULPHATE, AND OXALATE OF AMMONIA HAVE FAILED TO PRODUCE A PRECIPITATE (163) OR OF THE FLUID FILTERED FROM THE PRECIPITATES FORMED (164), add AMMONIA, THEN SOME PHOSPHATE OF SODA, AND, SHOULD A PRECIPITATE NOT AT ONCE FORM, RUB THE INNER SIDES OF THE GLASS-TUBE WITH A GLASS ROD, AND 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 § 197.-If no residue is left, this is a proof of the absence of the fixed alkalies; pass on at once to

$198.

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 some 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,

The most convenient way is to conduct the evaporation on the lid of a platinum crucible.

adding some chloride of ammonium during the process (to convert into chlorides the caustic alkalies or alkaline carbonates that may happen to form), ignite the residue gently, then dissolve 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 examine it according to the directions of § 197.

§ 197.

(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 (167), or in (168).

Dissolve it in a little water, filter if necessary, evaporate until 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 t'eat 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 (§ 89, 3).

2. To the other half of the fluid (on 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 § 90, 2.

§ 198.

(Examination for Ammonia.)

THERE REMAINS STILL THE EXAMINATION FOR AMMONIA. Tritu- 171 rate 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 litmuspaper adhering to the under side.

Complex Compounds.

A, 1. SUBSTANCES SOLUBLE IN WATER.

DETECTION OF ACIDS.*

I. In the Absence of Organic Acids.

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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; see (67) and (68).

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.t Pass on to (175).

b. A PRECIPITATE IS FORMED. Dilute the fluid, and add 174 hydrochloric acid or, as the case may be, nitric acid; if the precipitate does not redissolve, or at least not completely, SULPHURIC ACID is present.

If this 175

3. Add nitrate of silver to a portion of the solution. fails to produce a precipitate, test the reaction, and if acid, add to the fluid 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 will form 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 (181); there is neither chlorine, bromine, iodine,
cyanogen, ferro- and ferricyanogen present, nor sulphur; nor
phosphoric acid, arsenic acid, arsenious acid, chromic acid, silicic
acid, oxalic acid; nor boracic acid, if the solution was not too
dilute.

b. A PRECIPITATE IS FORMED.

Observe the colors of it, 177

then add nitric acid, and shake the mixture.

* Consult also the explanations in Section III.

+ 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 (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.