alkaline solution. The formation of a white precipitate indicates the presence of ZINC.

BB. If the original or the alkaline solution is green, and if the precipitate produced by soda and redissolved by an excess of the precipitant, was of a bluish color, SESQUIOXIDE OF CHROMIUM is present. To remove all doubt, heat the alkaline solution to boiling, or try the reaction before the blowpipe (§ 101).

77. Add chloride of ammonium to the alkaline solution. The formation of a white precipitate indicates the presence of ALUMINA. The reaction with solution of nitrate of protoxide of cobalt before the blowpipe will afford conclusive proof (§ 100).

4. Add to a portion of the original solution chloride of ammonium 62 and carbonate of ammonia, mixed with some caustic ammonia, and heat gently.

a. NO PRECIPITATE IS FORMED: absence of baryta, strontia, and lime. Pass on to § 180,5 (64).

b. A PRECIPITATE IS FORMED: presence of baryta, strontia, 63 or lime.

Add a considerable quantity of solution of sulphate of lime to a portion of the original solution.

a. The solution does not become turbid, not even after the lapse of from five to ten minutes: LIME. To remove all doubt,

test with oxalate of ammonia (§ 96).

B. The solution becomes turbid, but only after the lapse of

some time: STRONTIA.

sive proof (§ 95).

The alcohol flame will afford conclu

y. A precipitate is immediately formed: BARYTA. move all doubt, test with hydrofluosilicic acid (§ 94).

To re

5. Mix that portion of the solution of 4 in which carbonate of 64 ammonia has, after previous addition of chloride of ammonium, failed to produce a precipitate, with phosphate of soda, add some more ammonia, and rub the sides of the vessel with a glass rod.

a. No PRECIPITATE IS FORMED: absence of magnesia. Pass on to $180, 6 (65).

b. A CRYSTALLINE PRECIPITATE IS FORMED: MAGNESIA. 6. Evaporate a drop of the original solution on perfectly clean 65 platinum foil as slowly as possible, and gently ignite the residue.

a. THERE IS NO FIXED RESIDUE LEFT. Test for ammonia, by adding to the original solution hydrate of lime, and observing the odor and reaction of the escaping gas, and the fumes which it forms with acetic acid (§ 90).

b. THERE IS A FIXED RESIDUE LEFT: potassa or soda. Add 66 bichloride of platinum to a portion of the original solution, having first concentrated it by evaporation if dilute, and shake the mixture.

a. No precipitate is formed, not even after the lapse of ten or fifteen minutes: SODA. The blowpipe flame and alcohol flame are selected as conclusive tests, or the reaction with antimonate of potassa is resorted to for the purpose (§ 89).

B. A yellow crystalline precipitate is formed: POTASSA.

The reaction with tartaric acid, the blowpipe flame and
alcohol flame are selected as conclusive tests (§ 88).

Simple Compounds.

A. SUBSTANCES SOLUBLE IN WATER.

DETECTION OF THE ACID.

I. Detection of Inorganic Acids.

$181.

Reflect in the first place which of the inorganic acids form soluble compounds with the detected base (compare Appendix IV.), and bear this in mind in your subsequent operations.

1. ARSENIOUS ACID and ARSENIC ACID have already been consi- 67 dered in the preceding paragraph (detection of the base). These two acids are distinguished from each other by their respective behavior with nitrate of silver, or with potassa and sulphate of copper (see § 133).

2. The presence of CARBONIC ACID, HYDROSULPHURIC ACID, and 68 CHROMIC ACID, is also indicated already in the course of the process pursued for the detection of the bases. The two former betray their presence by effervescing upon the addition of hydrochloric acid; they may be distinguished from one another by their odor. Should additional proof be required, the presence of carbonic acid may be ascertained beyond a doubt by the reaction with lime-water (see § 149), and that of hydrosulphuric acid by the reaction with solution of acetate of lead (§ 156). The presence of chromic acid is invariably indicated by the yellow or red tint of the solution, as well as by the transition of the red or yellow color to green, accompanied by the separation of sulphur, upon the addition of hydrosulphuric acid water. To remove all doubt, try the reactions with solutions of acetate of lead and of nitrate of silver (§ 138, b).

3. Add some chloride of barium to a portion of the solution, then- 69 if the fluid has remained clear, and the reaction is acid-ammonia to slightly alkaline reaction.

a. THE FLUID REMAINS CLEAR. Pass on to 181, 4 (71). The absence of sulphuric acid, phosphoric acid, and silicic acid is certain, that of oxalic acid and boracic acid probable; as the baryta compounds of the two latter acids are kept in solution by ammoniacal salts, whilst borate of baryta does not separate from dilute solutions, even in the absence of ammoniacal salts.

b. A PRECIPITATE IS FORMED.

in moderate excess.

Add dilute hydrochloric acid 70

a. The precipitate dissolves: absence of sulphuric acid. Pass on to 4 (71).

6. The precipitate remains undissolved, even on the addition

of a large quantity of water: SULPHURIC ACID.

4. Add solution of sulphate of lime to another portion of the 71 solution (which, if it has an acid reaction, must first be neutralized, or made slightly alkaline, by means of ammonia). If no salt of ammonia is present, add some chloride of ammonium before adding the solution of sulphate of lime.

a. No PRECIPITATE IS FORMED: absence of phosphoric acid, silicic acid, oxalic acid, and fluorine. Pass on to 5 (73). b. A PRECIPITATE IS FORMED. Add acetic acid in excess.

a. The precipitate redissolves readily: PHOSPHORIC ACID or SILICIC ACID. The reaction with molybdic acid (§ 143) will afford conclusive proof of the presence of the former acid; to obtain positive certainty as to the presence of the latter, evaporate the solution, acidified with hydrochloric acid, to dryness, and treat the residue with hydrochloric acid.

B. The precipitate remains undissolved or dissolves with difficulty: OXALIC ACID or FLUORINE. Oxalate of lime is pulverulent, fluoride of calcium flocculent and gelatinous. The reaction with binoxide of manganese and sulphuric acid (§ 146) will afford conclusive proof of the presence of oxalic acid; the reaction on glass (etching) of the presence of fluorine (§ 147).

72

5. Acidify a fresh portion of the original solution with nitric acid, 73 and add solution of nitrate of silver.

a. THE FLUID REMAINS CLEAR. This is a proof of the absence of chlorine, bromine, iodine, ferrocyanogen, and ferricyanogen; the absence of cyanogen (in simple cyanides) is also probable. Of the soluble metallic cyanides, cyanide of mercury is not precipitated by nitrate of silver; if, therefore, in the analytical process for the detection of the bases, mercury has been found, cyanide of mercury may be present. For the manner of detecting the cyanogen in the latter, see § 155, 8. Pass on to 6 (76).

b. A PRECIPITATE IS FORMED.

a. The precipitate is orange : FERRICYANOGEN; the reaction 74 with sulphate of protoxide of iron is resorted to as a confirmatory test (§ 155, Appendix).

B. The precipitate is white or yellowish-white. Add ammonia in excess.

aa. The precipitate is not dissolved: IODINE or FERROCYANOGEN. In the former case the precipitate is pale yellow, in the latter white and gelatinous. The reaction with starch and hyponitric acid (§ 154) will afford conclusive proof of the presence of iodine, the reaction with sesquichloride of iron of the presence of ferrocyanogen (§ 155, Supplement).

BB. The precipitate is dissolved: CHLORINE, BROMINE, 75 or CYANOGEN. If the original substance smells of hydrocyanic acid, and the silver precipitate dissolves with some difficulty in the ammonia, the precipitate may be assumed to consist of cyanide of silver, and, consequently, to indicate the presence of CYANOGEN. To remove all doubt on the point, add to the original solution sulphate of protoxide of iron, solution of soda, and hydrochloric acid (§ 155). If addition of chlorine water imparts a yellow tint to the original solution the precipitate may be held to consist of bromide of silver, and consequently indicates the presence of BROMINE; if the bromine is present only in very small proportion, ether must be used in conjunction with

chlorine water to make the reaction distinctly apparent
(§ 153). In the proved absence of both bromine and
cyanogen, the precipitate consists of chloride of silver, and
consequently shows the presence of CHLORINE.

6. Add to a small portion of the aqueous solution hydrochloric 76 acid, drop by drop, until a distinct acid reaction is just imparted to the fluid, then dip in a slip of turmeric paper, take it out, and dry it. If the dipped portion looks brownish-red, BORACIC ACID is present. To settle all doubt on the point, add sulphuric acid and alcohol, and set fire to the latter (§ 145).

7. With regard to NITRIC ACID and CHLORIC ACID, these are 77 usually discovered already in the course of the preliminary examination (see $174, 2, c [6]). The reaction with sulphate of protoxide of iron and sulphuric acid (§ 159) will afford conclusive evidence of the presence of the former, treatment of the solid salt with concentrated sulphuric acid, of the presence of the latter acid (§ 160).

Simple Compounds.

DETECTION OF THE ACID.

A. SUBSTANCES SOLUBLE IN WATER.
II. Detection of Organic Acids.
§ 182.

1. Add ammonia to a portion of the compound under examination to slight chloride of calcium. If the solution was acid, add chloride of ammonium before calcium.

aqueous solution of the 78 alkaline reaction, then neutral, or only slightly adding the chloride of

a. No PRECIPITATE IS FORMED, NOT EVEN AFTER SHAKING THE FLUID NOR AFTER THE LAPSE OF A FEW MINUTES: absence of oxalic acid and tartaric acid. Pass on to § 182, 2 (80).

b. A PRECIPITATE IS FORMED. Add lime-water in excess 79 to a fresh portion of the original solution, and then add solution of chloride of ammonium to the precipitate formed.

The re

a. The precipitate redissolves: TARTARIC ACID.
action with acetate of potassa may be resorted to as a confir-
matory test; but a still more positive proof will be afforded
by the deportment which the precipitate produced by the
chloride of calcium, and properly washed, exhibits with solu-
tion of soda or with ammonia and nitrate of silver (§ 162).
6. The precipitate does not redissolve: OXALIC ACID.
remove all doubt, try the reaction with concentrated sul-
phuric acid (§ 146).

To

2. Heat the fluid of 1, a, to boiling, keep at that temperature 80 for some time, and add some more ammonia to the boiling fluid.

a. IT REMAINS CLEAR: absence of citric acid. Pass on to § 182, 3 (81).

b. IT BECOMES TURBID, AND DEPOSITS A PRECIPITATE: CITRIC ACID. To remove all doubt as to the nature of the acid, add solution of acetate of lead in excess, wash the precipitate formed, and see whether it dissolves readily in ammonia (§ 163). 3. Mix the fluid of 2, a, with alcohol.

81

a. IT REMAINS CLEAR: absence of malic acid. Pass on to § 182, 4 (82).

b. A PRECIPITATE IS FORMED: MALIC ACID. To remove all doubt, it is invariably necessary to try the reaction with acetate of lead to see whether the precipitate produced by that reagent dissolves with difficulty in ammonia, and to examine its deportment when the fluid in which it is suspended is heated to boiling (§ 164).

4. Neutralize a portion of the original solution completely (if not already absolutely neutral) with ammonia or with hydrochloric 82 acid, and add solution of sesquichloride of iron.

a. A, BULKY PRECIPITATE FORMS, OF A CINNAMON BROWN, OR DIRTY YELLOW COLOR. Wash the precipitate, heat it with ammonia, filter, concentrate the filtrate by evaporation, divide into two parts, and add to the one some hydrochloric acid, to the other alcohol and chloride of barium. The formation of a precipitate in the first portion indicates the presence of BENZOIC ACID, a precipitate in the second denotes the presence of SUCCINIC ACID. Compare § 167 and § 168.

6. THE LIQUID ACQUIRES A RATHER INTENSE DEEP RED TINT, 83 AND, UPON PROTRACTED BOILING, A LIGHT REDDISH-BROWN PRECIPITATE SEPARATES: acetic acid or formic acid. Heat a portion of the solid salt under examination, or, if the substance is in the fluid state, of the residue left upon evaporating the fluid (which, if acid, you must neutralize first with soda), with sulphuric acid and alcohol (§ 170). The characteristic odor of acetic ether indicates the presence of ACETIC ACID.

If do not detect acetic acid in the fluid, you may conyou clude that the substance under examination contains FORMIC ACID to remove all doubt, try the reactions with nitrate of silver and chloride of mercury (§ 171).

Simple Compounds.

B. SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WATER, BUT SOLUBLE IN HYDROCHLORIC ACID, NITRIC ACID, OR NITROHYDROCHLORIC ACID.

Detection of the Base.*
§ 183.

Dilute a portion of the solution in hydrochloric acid, nitric acid, 84 or nitrohydrochloric acid with water,† and proceed exactly as directed § 180, beginning at 1 (46), in cases where the substance is dissolved in nitric acid, and at 2 (50), if the solution already contains hydrochloric acid. Particular regard must be had in this to the following observations: we have seen § 180, 3, b, f, cc (59), that if, in cases where we

*Regard is also had here to certain salts of the alkaline earths, as this course of examination leads directly to their detection.

If upon the addition of water the liquid becomes white and turbid or deposits a white precipitate, this indicates the presence of antimony or bismuth. Compare § 176, 4 (29). Heat with hydrochloric acid until the fluid has become clear again, and then pass on to § 180, 2 (50).