and test for magnesium by sodium phosphate test* (s. Table for Gr. VI.).

V.

GROUP IV. To filtrate from Gr. III. add a few drops of ammonium sulphide :—

VI. GROUP V. To filtrate from Gr. IV. add ammonium carbonate, collect pp., wash it, dissolve in HClAq, and divide liquid into two parts :—

VII. GROUP VI. Divide filtrate from Gr. V. into two

*The Mg phosphate or oxalate is decomposed by the Na,CO, MgCO3 is formed and Na phosphate or oxalate dissolves in the wash-water.

B.

Detection of commonly occurring acids when not more than one is present in any group*.

I. Test for nitric acid by ferrous sulphate test (s. Part I. Chap. VII. Exp. 4).

II. GROUP I. To original solid (if liquid is given evaporate to dryness on steam-bath) add concentrated sulphuric acid:

Colourless non-inflammable gas (CO) evolved; gas produces white pp. in lime

water,

H.CO3.

Colourless strongly
fuming gas evolved,
probably HC1
(confirm; s. Gr. IV.)

Colourless badly-smell-
ing gas evolved, and
generally white solid
(S) deposited,
H.S

(confirm; s. Gr. III.)

If no reaction occurs with sulphuric acid in the cold, then

To prepare the solution for the remaining groups, add a large excess of solid sodium carbonate to the original liquid, or if original is a solid add Na,CO, and a little watert; boil for 5-10 mins., filter off the pp. of metallic carbonates, just acidify the filtrate by adding dilute nitric acid, boil, and filter again if necessary. The solution should now be neutral; if not, make it so by very cautious addition of very dilute ammonia.

III. GROUP II. To a portion of the neutral liquid add barium nitrate solution; if a white pp. forms add to it dilute nitric acid :—

* Chromic, arsenic, and arsenious, acids, if present, will have been detected in testing for metals.

+ If the addition of excess of Na,CO,Aq to a little of the original liquid produces no pp. the treatment with Na,CO, described above is unnecessary; the liquid must however be neutral before examining for

Grs. II. and III.

Treatment with Na,CO, removes metals, that would interfere with the subsequent tests for acids, by pptg. them as carbonates; the filtrate contains sodium salts of the acids.

IV. GROUP III. To a portion of the neutral liquid add neutral ferric chloride solution:

V.

HCNS.

GROUP IV. To two or three drops (not more) of silver nitrate solution in a very clean test tube add a drop or two of the original liquid :

III. Spec. gravities and compositions of aqueous solutions of Acids, Alkalis, and Alcohol.