2CCl3CH(OH)2 + MgO = 2CHCl3 + (HCOO)2Mg + H2O.
The fluid may now be tested for formic acid: it will give a black precipitate with solution of silver nitrate—
(HCOO)2Mg + 4AgNO3 = 4Ag + Mg(NO3)2 + 2CO2 + 2HNO3.
It will give a white precipitate of calomel when treated with mercuric chloride solution—
(HCOO)2Mg + 4HgCl2 = 2Hg2Cl2 + MgCl2 + 2HCl + 2CO2.
Chloral (or chloroform), when boiled with resorcinol and the liquid made strongly alkaline with NaHO, gives a red colour, which disappears on acidifying and is restored by alkalies. If, on the other hand, there is an excess of resorcinol and only a very small quantity of NaHO used, the product shows a yellowish-green fluorescence; 1⁄10 of a milligramme of chloral hydrate gives this reaction distinctly when boiled with 50 mgrms. of resorcinol and 5 drops of a normal solution of sodium hydrate.[191]
[191] C. Schwarz, Pharm. Zeit., xxxiii. 419.
Dr. Frank Ogston[192] has recommended sulphide of ammonium to be added to any liquid as a test for chloral. The contents of the stomach are filtered or submitted to dialysis, and the test applied direct. If chloral is present, there is first an orange-yellow colour; on standing, the fluid becomes more and more brown, then troubled, an amorphous precipitate falls to the bottom, and a peculiar odour is developed. With 10 mgrms. of chloral in 1 c.c. of water, there is an evident precipitate, and the odour can readily be perceived; with 1 mgrm. dissolved in 1 c.c. of water, there is an orange-yellow colour, and also the odour, but no precipitate; with ·1 mgrm. in 1 c.c. of water, there is a weak, pale, straw-yellow colour, which can scarcely be called characteristic. The only substance giving in neutral solutions the same reactions is antimony; but, on the addition of a few drops of acid, the antimony falls as an orange-yellow precipitate, while, if chloral alone is present, there is a light white precipitate of sulphur.