expel from the filtrate the excess of CO2 by acidifying with acetic acid and finally neutralize the solution with the least possible amount of NH.OH.

EXAMINATION OF THE NA2CO PRECIPITATE FOR SILICIC, PHOSPHORIC AND OXALIC ACIDS.

Treat one portion of the precipitate with HNO1 and evaporate the solution to dryness. Digest the residue with water, add HNO and filter. A white gritty powder which when fused in a bead of "microcosmic salt" dissolves and floats in the bead, shows the presence of silicic acid.

To the above filtrate add an excess of ammonium molybdate in nitric acid, warm and let the test stand. The formation of yellow crystalline ammonium phosphomolybdate, shows the presence of phosphoric acid.

Treat another portion of the precipitate with acetic acid and filter to remove any insoluble residue. Boil the filtrate to remove all traces of CO2, and then add CaSO. or CaCl2. A white powdery precipitate shows the presence of oxalic acid. If a fluoride were present the precipitate with these reagents would be gelatinous and nearly colorless.

If silicates and fluorides are both present they will likely combine forming either silicon fluorides or hydrofluosilicic acid.

GROUPS OF THE ACIDS.

Group I.

Acids decomposed by the stable mineral acids with the evolution of a gas.

Carbonic evolves CO, which clouds lime water.

Sulphurous evolves SO, which has the odor of burning sulphur.
Nitrous evolves NO which forms brown fumes with the air.

Hydrosulphuric evolves HS which has a stale egg odor.
Hydrocyanic evolves HCN which has a bitter almond odor.
Acetic evolves HC,H,O2 with H2SO, and forms a red solution with
FeCl3.

Group II.

Acids precipitated from neutral solutions by Calcium Acetate.

Arsenious, white, soluble in excess or in acetic acid.
Boric, white, soluble in excess or in acetic acid.
Carbonic, white, soluble in acetic acid with effervescence.
Hydrocyanic, white, soluble in excess or in acetic acid.

Phosphoric, white, soluble in acetic acid.

Tartaric, white, soluble in acetic acid.

Hydrofluoric, white, insoluble in acetic acid.

Oxalic, white, insoluble in acetic acid.

Silicic, white, insoluble in acetic acid and in all dilute acids.

Group III.

Acids precipitated by Barium Acetate.

Chromic, yellow, soluble in warm HCl.

Sulphuric, white, insoluble in HCl or HNO1.

Group IV.

Acids precipitated by Silver Acetate in the presence of acetic acid or by Silver Nitrate in the presence of nitric acid.

Hydroferrocyanic, white, soluble in KCN: insoluble in NH.OH. Sulphocyanic, white, curdy, soluble in NH2OH.

Hydroferricyanic, orange red, soluble in NH,OH and in KCN. Hydrocyanic, white, soluble in KCN and in NH,OH

Hydriodic, light yellow, slightly soluble in NH,OH, easily in KCN. Hydrobromic, yellowish white, difficultly in NH,OH, soluble. Hydrochloric, white, curdy, easily soluble in NH,OH. Hydrosulphuric, black, soluble in hot dilute HNO,.

Group V.

Acids not precipitated in the preceding groups.

Arsenious gives yellow As2S2 with H2S in presence of HCl or HC,H,O..

Chloric gives a deep blue color with aniline sulphate and H2SO.. Nitric gives the "brown ring" test.

ANALYSIS OF THE ACIDS IN SOLUTION.

Use one third of the solution for the detection of the acids of Group I and the main portion for the detection of the acids of the other groups.

Group I.

This group includes the CO2, SO2, S, NO, C2H3O2 and CN ions which are liberated by such dilute acids as HCl or HNO1.

1. CO2. To a portion of the solution add a few drops of HCl. Effervescence and the evolution of a gas which clouds a drop of lime water shows the presence of carbonic acid.

2. SO. To a second portion add HCl and warm. The evolution of a gas having the odor of burning sulphur shows the presence of sulphurous acid. Thiosulphuric acid gives a white or yellow precipitate of sulphur in addition to evolving SO2.

3. NO. Acidify a third part with acetic acid or dilute H2SO, and add some FeSO,. A yellow brown or black brown coloration shows the presence of nitrous acid.

4. S. Acidify another portion with HCI and warm. If a gas is liberated which has a stale-egg odor or which blackens a strip of "lead acetate paper," HS is present.

5. CH2O2. To a fifth portion add a little alcohol, a few drops of conc. H2SO, and gently warm. The formation of ethyl acetate which has a characteristic odor shows the presence of acetic acid. Apply this test in the absence of chlorates, chromates, cyanides, and iodides. 6. CN. See Group IV, A (4).

Group II.

This group contains the acids which are precipitated from neutral solutions by Calcium Acetate.

A. Boric, Phosphoric, Carbonic, Hydrocyanic and Tartaric acids which are soluble in acetic acid.

B. Hydrofluoric, Oxalic and Silicic acids which are insoluble in acetic acid.

To the major portion of the solution add conc. aqueous calcium acetate Ca(C2H2O2)2 in very slight excess. A white precipitate shows the presence of one or more members of this group. Filter, wash the precipitate twice with cold water and reserve the filtrate and washings for treatment under the next group.

Treat the precipitate on the filter with acetic acid passing the acid solution through the filter as long as any of the precipitate dissolves. Wash any insoluble residue twice with cold water and treat the filtrate under A and the residue under B.

A.

Divide A into four portions. Note that CN and CO: are both precipitated by calcium acetate but the former is more or less soluble in water and both are decomposed by acetic acid, causing effervescence in the case of a carbonate and giving the odor of bitter almonds with a cyanide (poison).

1. BO. Evaporate one portion to about one half its volume and acidify it with normal HCI. Saturate a strip of turmeric paper with this solution and dry it at a gentle heat. If the strip assumes a pale rose-red color which in turn becomes greenish-black on adding a drop of KOH, boric acid is present.

2. PO. To a second portion add an excess of an ammonium molybdate solution, warm and let stand. A yellow crystalline precipitate shows the presence of phosphoric acid. Arsenic acid gives a similar precipitate.

3. CHO. Evaporate a third portion to dryness, add a drop or so of conc. H2SO, and again heat. If the residue blackens and yields an odor of "burnt sugar," tartaric acid is present.

Since boric acid redissolves somewhat after being precipitated by calcium acetate, it will be necessary to test for it again under Group V.

B.

1. F. Test a portion of the residue which was insoluble in acetic acid as follows: Cover a piece of window glass or a small watch glass with a thin coating of wax and when the wax is cold remove a portion of it with some sharp instrument. Mix the residue to be tested with enough conc. H2SO, to make a paste and cover the exposed parts of the glass with the mixture. Let the test stand for fifteen minutes, then clean the glass and see if it has been etched where exposed. If so, hydrofluoric acid is present.

2. CO. Place another portion of the residue in a test-tube with a little MnO, and cover it with H2SO,. While boiling hold in the escaping vapor a drop of clear lime water on the end of a glass rod. If the drop becomes cloudy due to the liberation of CO2, oxalic acid is present.

3. SO2. Treat a third portion with HCl and evaporate to dryness. Digest the residue with H2O and HCl and filter. A white gritty in

soluble powder indicates silicic acid as SiO. See page 2.

Group III.

This group contains Chromic and Sulphuric acids which are precipitated from the filtrate of Group II by Barium Acetate.

To the filtrate from Group II add a slight excess of barium acetate Ba (C2H2O2), and agitate. A fine white precipitate shows the presence of sulphuric acid and in that case, filter and pass to the next group. A fine yellow precipitate indicates chromic acid. If a precipitate forms, filter, wash, and reserve the filtrate for treatment under Group IV.

1. Cro.. Transfer the precipitate to a test tube and warm with dilute HCl. Any chromate present will dissolve to a yellow solution, the white sulphate when present remaining undissolved. Filter, wash and confirm the presence of chromic acid by acidifying with acetic acid and adding lead acetate for yellow lead chromate.

2. SO,. Any white residue insoluble in dilute HCl or HNO, confirms the presence of sulphuric acid.

Group IV.

This group contains Hydroferrocyanic, Sulphocyanic, Hydroferricyanic, Hydrocyanic acids classified under portion A and Hydriodic, Hydrobromic, Hydrochloric acids, classified under portion B, which are precipitated by Silver Acetate from acetic acid solutions or by Silver Nitrate from nitric acid solutions.

Strongly acidify the filtrate from the last group with acetic acid, add silver acetate in slight excess and gently warm, not boil. Filter, wash twice and reserve the filtrate for later treatment. Divide the precipitate into two portions "A" and "B."

PORTION A.

Agitate "A" with a mixture of one part of dilute HCl and three parts of a solution of sodium chloride (1-10) which dissolves the cyanides. Filter and reject the precipitate. Divide the filtrate into three parts.

1. Fe(CN),"". To one portion add FeCl, as long as a precipitate forms. A dark blue precipitate shows the presence of hydroferrocyanic acid. Filter.

2. CNS. If the filtrate from (1.) has a blood red color which is destroyed by HgCl2, sulphocyanic acid is present.

3. Fe (CN)". To a second portion add a crystal of FeSO, or a freshly prepared solution of FeSO,. A dark blue precipitate shows the presence of hydroferricyanic acid. Or the fitrate from (1) may be boiled with H2SO, and more FeCl, added. A dark blue precipitate shows the presence of the acid.

4. CN. To a third portion add a little picric acid, and excess of NH,OH and warm. If on standing a light or dark mahogany color appears, hydrocyanic acid is present.

PORTION B.

Place portion "B" of the precipitate in an evaporating dish with a few pieces of zinc, cover with water, add a few drops of H.SO. and gently warm. When the reduction of the silver salts is complete, indicated by a black precipitate, filter and reject the precipitate. Neutralize the filtrate with Na2CO3, filter, reserve the filtrate and reject the precipitate.

1. I and Br. Test a portion of the filtrate as follows: Add to the test an equal volume of CS, and then nitro-sulphuric acid (1:1) drop by drop, vigorously agitating after the addition of each drop and noting the color of the CS2. If the latter becomes pink or violet, HI is present; if yellow, yellow-brown or red-brown, HBr is present. The iodine is first liberated and the colored sulphide may be removed by filtering. To the filtrate add more CS, and repeat the operation. When all the I has been removed any liberated Br will in turn color the CS,. 2. Acidify a second portion of the solution with HNO, and add AgNO, in slight excess. Filter, wash, reject the filtrate and boil the precipitate with an excess of "sesqui" ammonium carbonate. Decant the clear liquid, add a fresh portion of the carbonate and again boil. Decant as before and to the decanted liquids add enough HNO, to acidify. The formation of a white curdy precipitate shows the presence of hydrochloric acid. (Hager's Test.)

In the absence of HI and HBr add to the test solution AgNO3. A white curdy precipitate which is insoluble in HNO, and which readily dissolves in NH,OH, shows the presence of HCl.