---

For any bees wanting some good formic, heres a tip, go and buy it, forget trying to get it from oxalic acid.

---

From Cohen's Practical Organic Chemistry

Formic Acid
Berthelot, Ann. Chim. Phys., 1856, (3) 46, 477 ; Lovin, Bull. Soc. Chim., 1866, (2) 5, 7 ; 1870, (2) 14, 367.

50 grams. anhydrous glycerol.
200 grams oxalic acid (in four portions of 50 grams).

The glycerol is dehydrated by heating it gently in a basin on a sand-bath until a thermometer with the bulb immersed in the liquid indicates 175°. Fifty grams of commercial crystallised oxalic acid and 5o grams of glycerol are heated in a retort (250 c.c.) over wire-gauze, with condenser and receiver. A thermometer is fixed through the tubulus with the bulb in the liquid. The reaction begins at about 80°, and at 90° proceeds briskly, carbon dioxide being evolved. The temperature is maintained at 105-110° until the evolution of gas has slackened. Some aqueous formic acid has meanwhile collected in the receiver. The contents of the retort are now cooled to about 80° and a further 50 grams of oxalic acid added. The reaction recommences on heating with the formation of aqueous formic acid, which becomes more concentrated with each fresh addition of oxalic acid until the distillate eventually contains 56 per cent. of acid. The other portions of oxalic acid are added in the same way. In order to regain the formic acid which remains as monoformin in the retort, the contents are transferred to a round flask, diluted with about 250 c.c. of water and distilled in steam, until the distillate has only a faintly acid reaction (about 250 c.c.).
Distillation in Steam.- A large flask, or preferably, a 1 gallon tin is closed by a double bored cork. A safety-tube passes through one hole, and a bent tube which terminates below the Cork passes through the second hole, and is attached by rubber tubing to the inlet tube of the distilling flask (1 litre). The flask is sloped to prevent the contents being splashed over into the condenser. It is heated on the sand bath or asbestos board to boiling, and steam passed in. The united distillates are poured into a basin and neutralised by adding lead carbonate until, on heating, no further effervescence occurs. The liquid is now left for a moment to settle, and the clear solution decanted, whilst hot, through a fluted filter. The residue in the basin is boiled up again with a volume of water equal to that decanted, and again a third and fourth time, and filtered hot each time until no more lead formate is dissolved. The lead formate will have now passed into solution and the liquid is then evaporated down on a sand-bath or ringburner, until crystals appear on the surface, when the liquid is put on one side to cool. Lead formate crystallises out in long white needles. Yield about 150 grams. In order to obtain pure formic acid, hydrogen sulphide is passed over the heated lead salt. It is carried out as follows:
The powdered salt, dried on the water­bath, is introduced in a long layer into a sloping wide tube, loosely stopped at the lower end by a plug of glass wool or asbestos. To the lower end of the tube a receiver, in the form of a distilling flask, is attached, which is protected from moisture by a drying-tube. The salt is heated gently by moving a flame along the tube whilst hydrogen sulphide, washed through water, and dried by passing through a U-tube containing calcium chloride, is led over the salt in not too rapid a stream. The lead formate blackens, and is slowly converted into lead sulphide and formic acid, which drops into the receiver. The acid, which retains a strong smell of hydrogen sulphide, is freed from the latter by distillation over a little dry lead formate. Yield is nearly theoretical.