INDIGO. PICRIC ACID.

149

EXERCISE X. (See (234) for Examples for Practice.)

172. IDENTIFICATION OF THE MORE COMMON ORGANIC SUBSTANCES.*

1. SOLID ORGANIC SUBSTANCES.

A. Characterized by color.

173. Indigo, C.H.NO.-Dark blue. Insoluble in water, alcohol, and ether.

Heated in a tube (17), yields violet vapors, smelling of

aniline and ammonia.

Strong sulphuric acid slowly dissolves indigo, when heated, giving a blue solution, which is changed to brown-yellow by nitric acid.

Shaken in a corked tube with sulphate of iron (ferrous sulphate) and slaked lime, and allowed to settle, indigo dissolves to a yellow solution (reduced indigo, C.H.NO), which becomes blue-green when decanted and acidulated with hydrochloric acid.

6

174. Picric or Carbazotic Acid, HC,H,O3NO,.-Yellow crystals. Very bitter. Stains the skin yellow.

Water dissolves it sparingly. Bright yellow solution. Alcohol dissolves it easily. The solution gives a yellow crystalline precipitate when stirred with a little potash. Heated in a tube, fuses, and sometimes explodes slightly. Strong sulphuric acid dissolves it, and deposits it unchanged on addition of water.

Heated with solution of chloride of lime (bleaching powder), it evolves a very pungent odor like oil of mustard, due to chloropicrine, CCI,NO,.

175. Caramel, C12HO,.-Dark-brown.

Slightly bitter.

18

Very soluble in water, dark-brown solution.

Sparingly soluble in strong alcohol.

Deliquescent.

* Excluding those which are treated of in Exercises 8 and 9.

Heated in tube, carbonizes, and emits the odor of burnt sugar.

Strong sulphuric acid carbonizes it.

B. Characterized by Odor.

176. Carbolic Acid (Phenic Acid); Phenole, CH ̧O. Moist needle-like crystals; colorless or pale brown. Powerful odor of coal-tar. Very easily melted. Water dissolves it sparingly. Easily soluble in potash.

Alcohol dissolves it readily.

Perchloride of iron (ferric chloride) gives a dark purpleblue color with the aqueous solution of carbolic acid.

Dropped into strong nitric acid, carbolic acid. is oxidized with great violence, yielding a red solution; if this be boiled and allowed to cool, it deposits prismatic crystals of picric acid which may be identified by (174).

176a. Hydrate of Chloral, CHCI,O.H2O., white crystalline solid. Easily dissolved by water.

Remarkable pungent odor.

Easily melted and volatilized.

Heated with potash, yields an oily-looking layer of chloroform and a solution of formiate of potash, which may be identified by neutralizing with dilute sulphuric acid, adding nitrate of silver in excess, decanting the clear liquid from any precipitated chloride of silver, and boiling it, adding ammonia, drop by drop, when metallic silver is precipitated.

C. Without Characteristic Color or Odor.

Examine by Table P.

TABLE P.

NOTES TO TABLE P.

178. The commonest of these organic substances which are dissolved to any considerable extent by being shaken with cold water are-*

179. Cane-sugar, C,,H,,O,,, identified.

12 22

Add to the solution a few drops of sulphate of copper, and, drop by drop, potash. The blue precipitate first produced redissolves in the excess of potash, to a blue liquid. Boil for some minutes, suboxide of copper (cuprous oxide) is deposited, first as a yellow hydrate, afterwards as the red anhydrous oxide.

To another part of the solution, add excess of potash, and boil, only a very light-brown color should be produced.

Heat a portion of the solid substance with strong sulphuric acid, which should carbonize it almost immediately.

To a part of the aqueous solution, add a few drops of dilute hydrochloric acid, and boil for a few minutes; the cane-sugar is thus converted into grape-sugar, which may be identified by the following tests.

180. Grape-sugar, C,H,,O,, identified.

Add to the solution an excess of potash, and boil. liquid should assume a rich brown color.

The

To another part of the solution, add a few drops of sulphate of copper, and, drop by drop, potash. The blue precipitate. first produced redissolves in the excess of potash, to a blue liquid, which deposits suboxide of copper when heated (at

*See foot-note on page 154.

MILK-SUGAR.

UREA.

PYROGALLIN.

153

first yellow and afterwards red) more readily than in the case

of cane-sugar.

Heat a portion of the solid substance with strong sulphuric acid it should not carbonize so readily as cane-sugar. Grape-sugar is much less sweet than cane-sugar.*

181. Milk-sugar, C12HO12, identified.

12 24

Very much less sweet than either cane- or grape-sugar.

Feels gritty between the teeth. Almost insoluble in ordinary alcohol, which dissolves cane- or grape-sugar on heating.

Answers to the same tests as grape-sugar.

182. Urea, C,H ̧ÑO,, identified.

Prismatic crystals. Resembles nitre in appearance and taste. Very soluble in water and alcohol.

Heated in a tube, melts easily, and evolves much ammonia. A pretty strong aqueous solution of urea, stirred with concentrated nitric acid in excess, and allowed to stand, deposits scaly crystals of nitrate of urea.

If a strong solution of oxalic acid be substituted for nitric acid, crystals of oxalate of urea are deposited.

If a solution of urea be mixed with a solution of mercuric nitrate, a white precipitate is produced.

On adding excess of silver nitrate to solution of urea, and boiling down, in a test-tube, to a small bulk, a crystalline precipitate of silver cyanate separates on cooling; if this precipitate be heated with dilute hydrochloric acid, it effervesces, and evolves the pungent odor of cyanic acid; on adding potash, and boiling, the odor of ammonia is perceived.

183. Pyrogallic acid or Pyrogallin, CHO,, identified. White or slightly brown crystalline powder. Often

* Sugar of fruits (fructose or uncrystallizable sugar) answers to the same taste as grape-sugar.

Prepared by adding finely-powdered red oxide of mercury to hot nitric acid as long as it is dissolved.