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by passing steam into the outer tube of the condenser. Sulphuretted hydrogen washed through water and

then dried by passing over calcium chloride is led over the salt in not too rapid a stream.

The arrange

FIG. 30.

ment of the apparatus is shown in Fig. 30. The lead formate blackens, and is slowly converted into lead sulphide and formic acid, which flows down into the receiver. The acid, which retains a strong smell of sulphuretted hydrogen, dissolved in the acid is freed from the latter by a second distillation over dry lead formate.

C3H5(OH)3 + C2H2O =

Glycerin Oxalic Acid

(OH)2 C3H5O.COH

(OH)2 C3H5 150.COH + CO, + H,O

Monoform.n.

+ H2O = HCO2H + С ̧Н5(OH)3

Formic Acid.

Properties.-Colourless liquid with a penetrating smell; b. p. 99°; sp. gr. 1°223 at 0°; solidifies below o° to colourless crystals; m. p. 8.6°; soluble in water and alcohol; decomposes on heating with silver and mercury salts, the metals being deposited.

PREPARATION LXXII.

ALLYL ALCOHOL, CHO CH2: CH.CH2OH

=

LITERATURE.-Cahours, Hofmann (1857), Ann. Ch. Pharm. 102, 285; Tollens, Henninger (1870), Ann. Ch. Pharm. 156, 129.

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A mixture of 50 grms. commercial powdered oxalic acid, 200 grms. commercial glycerin, and grm. salammoniac, are heated in a retort of about litre capacity over wire gauze with a Bunsen lamp.* Strong evolution of carbonic acid gas at first occurs, and the temperature, indicated by a thermometer inserted into the retort, remains for some time stationary at about 130°. As the temperature slowly rises, the evolution of gas slackens, and after a time (at about 180°) entirely ceases. When the temperature has reached 195° the receiver, which now contains aqueous formic acid, is changed. At 200-210° carbonic acid is again given off, and oily streaks are observed to run down the neck of the retort; at the same time a disagreeable penetrating smell is perceptible. By gently heating the contents of the retort, a temperature of 220-230° is maintained for some time, and when it has finally risen to 260° the distillation is stopped. The distillate is a mixture of allyl alcohol and water, and there is also present allyl formate, glycerin, and acrolein. Excess of glycerin remains behind in the retort, and may be used again by repeating the operation with a smaller quantity of oxalic acid (30-40 grms.) until the residue is too small or has become dark-coloured and thick. The whole of the allyl alcohol, together with a small quantity of formic acid, and acrolein, is obtained by submitting the distillate to a second distillation. The distillation

is this time continued until on treating the last portions with potassium carbonate no oily layer (usually of a faint yellow colour) separates. This occurs at about 105°. On adding solid potassium carbonate to the distillate, the allyl alcohol settles out as an oil. This is drawn off, and 5-10 per cent. powdered caustic potash added. After having been allowed to stand for twenty-four hours and well shaken or gently warmed for a short time, the liquid loses the smell of acrolein and at the same time assumes a brown colour. In order to abstract the last traces of water, which are obstinately retained, the allyl alcohol is left in contact with anhydrous baryta and then distilled.

CH2O+C3H8O3 = C3H7O2. O2CH + H2O + CO2
Oxalic Acid Glycerin Monoformin.

C2H2O2O2CH = C3H5OH + H2O + CO2
Allyl Alcohol.

Properties. Colourless liquid with a pungent odour; b. p. 96°; sp. gr. o858 at 0°.

PREPARATION LXXIII.

5

ALLYL IODIDE, C2H,I=CH2: CH.CH2I. LITERATURE.-Berthelot, de Luca (1855), Ann. Ch. Phys. (3) 43, 257; Tollens, Henninger (1870), Ann. Ch. Pharm. 156, 156; Saytzew, Kanonikoff (1877), Ann. Ch. Pharm. 185, 191; Wagner (1876), Ber. 9, 1810.

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Through a mixture of 100 grms. glycerin dehydrated at 175°, and 70 grms. dry powdered iodine, contained in a retort of about 1-litre capacity and connected with condenser and receiver, a slow current of dry carbonic acid is passed.* 23 grms. yellow phosphorus cut into pieces about the size of a pea and dried between filter-paper are gradually added. The action is assisted at first by gently warming the retort with a small flame. A rather violent reaction then sets in, which is maintained by the addition of more phosphorus, and must be so regulated that the allyl iodide distils as it is produced; otherwise isopropyl iodide is formed. The distillate divides into two layers, and is coloured by dissolved iodine, which has been carried over. The lower layer is washed with dilute caustic soda solution and with water, and is separated from the aqueous portion by a tap-funnel. After dehydrating the liquid over calcium chloride it is distilled. The portion passing over at 98-102° is nearly pure allyl iodide and may be used for further experiments.

C3H5(OH)3 + I + P = С ̧H2I + P(OH)3
Allyl Iodide.

Glycerin

Properties.-Colourless liquid with an alliaceous odour; b. p. 101-102°; sp. gr. 1789 at 16.o

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