will be left if a ferrocyanide was present, and on acidifying the filtrate with HNO3 orange.red AgCfy, will precipitate. A sulphocyanide is found by (315).

The three following acid-radicles and their salts differ from the foregoing by being charred and emitting a smell of burning when heated in the solid state; oxalates, however, do so only to a slight extent. If the salt be one of the alkalis or of the alkaline earths, the residue left after ignition contains a carbonate which effervesces with an acid, whereas the original substance did not do so.

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317. Strong H2SO, heated with solid Am,O.2H,O causes an effervescence of gas consisting of a mixture of CO and CO2:

Am,C2O4 + H2SO4 = CO + CO2 + Am2SO+H2O.

The CO is detected by burning with a blue flame when a light is applied, the CO2 by rendering a drop of lime-water on a glass rod milky.

No blackening or charring is produced by strong H2SO4 ; oxalates differ in this respect from the salts of all other organic acids.

318. CaCl2 (CaSO4, or lime-water,) added to Am,C2O4 solution (made by diluting some of the reagent solution in a test-tube with an equal quantity of water), gives a white precipitate (CaC2O4), insoluble in AmHO and in HA, soluble in HCl or HNO3.

318 a. If this precipitate is filtered off, a portion placed on a watch-glass will not effervesce with dilute HC1; but if the remainder is dried and heated to dull redness on platinum foil, it is converted without blackening into CaCO,, which effervesces with dilute HCl.

Note. This is a general test for oxalate of K, Na, Ba, Sr, or Ca; oxalates of these metals leave carbonates on ignition which effervesce with an acid

319. Heated with MnO2 and H2SO4, solid oxalates give off CO,:

Am2C2O4 + MnO2 + 2H2SO4 = 2CO2+ MnSO4 +

Am2SO4+2H20.

Note.-Since commercial MnO, usually contains some carbonate, it will give off CO, when treated with H2SO4. If the MnO, to be used is not known to be free from carbonate the best way to perform the test is to add to some of the MnO, in a test-tube a little H2SO4, and heat to boiling; if CO2 is found in the tube by a glass rod with a drop of lime-water on its end continue to boil, occasionally drawing fresh air into the test-tube by pushing down a glass tube near to the surface of the liquid and sucking out the air; as soon as no CO2 is detectable in the tube after boiling for a short time and the liquid is distinctly acid, the Am,C,O4 is added and the mixture again heated, CO2 will be rapidly given off, and may be detected by the ordinary methods.

If the MnO, gives no CO2 with H2SO4 proceed at once to add the Am,C,O4, heat and test for CO2.

Hydrogen oxalate, or oxalic acid (H2C2O4, or crystallised H2C2O4.2H2O), when heated in a glass tube closed at one end partly sublimes unaltered, and is partly decomposed, yielding vapours which cause coughing; it yields reactions in pars. (317) and (319). It dissolves in water to an acid, poisonous liquid.

TARTRATES (-"CH12, or - "T).

Fora neutral Tartrate use Na2T.2H2O

or KNaT. For an acid tartrate use H2T or NaHT.

320. A solid tartrate or solid H2T when heated strongly in a tube chars, giving off a smell of burnt sugar.

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321. A solid tartrate or solid H2T heated with strong H2SO, blackens, giving off a mixture of CO, CO, and SO,. 322. AgNO, gives with solution of a neutral tartrate a white curdy precipitate (Ag2T), soluble in AmHO and in HNO. Allow some of the above precipitate (Ag2T) to settle in a test-tube, and pour off as much of the liquid from above it as possible; then pour very dilute AmHO drop by drop into the tube, until the precipitate, after being shaken up with the liquid, is nearly but not quite dissolved: then heat the test-tube gradually and gently (best by immersing it in a

beaker of cold water and slowly raising its temperature to 60°), a brilliant mirror of Ag will form on the interior of the tube. If the liquid, instead of being slowly raised to 60°, be quickly boiled, the Ag deposits as a black precipitate which is not so characteristic.

323. CaCl, precipitates from a neutral tartrate solution white or crystalline CaT: the precipitate often separates only after shaking the liquid well and letting it stand for a time; it is soluble in acids, and its formation is retarded by AmCl and other Am-salts. This precipitate is soluble in strong cold KHO,* is reprecipitated by boiling, but dissolves again more or less completely on cooling.

Decant the liquid from the precipitate and pour upon the precipitate a little very dilute AmHO in a test-tube, drop in a crystal of AgNO, and warm carefully as in par. (322). A silver mirror forms on the part of the glass on which the AgNO3 rests.

324. KCl (or better KĀ) if added to solution of H2T or an acid tartrate, gives on stirring or shaking a white crystalline precipitate (KHT). If HA is added at the same time, the precipitate may also be obtained with neutral tartrates. Addition of alcohol assists the formation of the precipitate, which is soluble in alkalis and in mineral acids.

325. If a few drops of FeCl solution be added to H,T or KNaT solution, then KHO (or AmHO) until the liquid is strongly alkaline, no precipitate forms. The precipitation of several other metals (e.g., Al, Mn, Cu) by alkalis is similarly prevented by H2T: this is owing to the formation of a double tartrate of the alkali-and the other metal, which salt is not decomposed by an alkali.

Hydrogen tartrate, or tartaric acid (HT), occurs in colourless crystals which do not alter in the air; they taste pleasantly acid, and dissolve in water and in alcohol. They are detected by heating them alone or with strong H,SO (320, 321): if dissolved and neutralised they also yield the reactions in (322, 323).

* A milkiness remaining, however, if the potash solution contains carbonate.

ACETATES ('C2H3O2, or 'A).—-Use NaÃ. 3H2O.

326. Solid NaA if strongly heated blackens, giving off a peculiar smell and a vapour (acetone) which burns with a bright flame when kindled.

327. Heated with strong H2SO4 vapour of Hà is given off, recognised by its pungent smell (that of vinegar). If alcohol be first added to the Naà then strong H2SO4, and the mixture warmed, a fragrant smell of ethyl-acetate (ETA) is emitted; it is most decided when the liquid is shaken after cooling for a short time.

328. FeCl added in small quantity to a little Naà dissolved in water, gives a deep red colour: on boiling the solution, made neutral but not alkaline with AmHO (if necessary), all the Fe separates as a light brown precipitate and the liquid becomes colourless. The red colour of the solution before being boiled is changed to yellow by addition of HCl (difference from the coloration due to sulphocyanide).

Hydrogen acetate, or acetic acid (HA)." Glacial acetic acid" is at 17° C. a colourless crystalline substance, possessing (especially when heated) a very pungent smell, and giving inflammable vapour : it is strongly acid. It dissolves in water readily, imparting its peculiar smell to the liquid in a mild degree. The acid is completely volatile without decomposition.

329. The above organic acid-radicles may be specially tested for by any of their reactions; (318) being generally used to test for an oxalate in solution, (317) or (319) when it is solid; a tartrate is best detected in solution by reaction (322) or (323), or if solid by (320); an acetate is found by (326) or (327).

*** After completing the reactions for the acid-radicles the student may proceed to try the preliminary examinations of solid substances for metals and acid-radicles, as directed in paragraphs (375-377), unless he is intending only to learn the analysis of simple salts, when he proceeds to Section V. (330 et seq.)

SECTION V.

ANALYSIS OF SIMPLE SUBSTANCES CONTAINING ONE METAL AND ONE ACIDRADICLE.*

Note. This section may be neglected by a student who is proceeding through the senior analytical course.

330. The ordinary method of proceeding to detect the metal or acid-radicle or both in a simple substance, is to make a few preliminary experiments, which will usually give some idea as to what substance is present, and will occasionally even detect metal or acid-radicle, or both of them, with certainty. If the composition of the substance has not been satisfactorily proved by this preliminary examination, the next process is to endeavour to dissolve the substance, if it is not already in the liquid form, in water or acids: then by adding to the solution certain group-reagents in the proper order of succession, it is found to which Analytical Group the metal present belongs. The following Table gives the analytical groups for metals, each group being headed by its distinctive number, name, and group-reagent :

Two metals may occasionally be present, as when an alum, or tartaremetic [K(SbO)T], is given for analysis; also there may be two acidradicles in the liquids given for analysis, since a salt insoluble in water is occasionally dissolved in an acid: but the student should always be informed of this if it in any way complicates the analysis. It will not usually do so, since in the most commonly occurring case, that of an alkaline earth phosphate dissolved in HCl, the (-"PO4) is detected in Group III. and accordingly no other acid-radicle is looked for.