Present name. - Sulphurous Anhydride. So2.

Sulphurous acid gas, dissolved in water, and constituting 9 "2 per cent. by weight of the solution.

Take of

Sulphuric Acid ....

4 fluid ounces;

Wood Charcoal, broken into small pieces . . . . .

1 ounce;

Water . . . . .

2 fluid ounces;

Distilled Water ....

20 fluid ounces.

Put the Charcoal and Sulphuric Acid into a glass flask, connected by a glass tube with a wash-bottle containing the 2 ounces of water, whence a second tube leads into a pint bottle containing the distilled water, to the bottom of which the gas-delivery tube should pass. Apply heat to the flask until gas is evolved, which is to be conducted through the water in the wash-bottle, and then into the distilled water, the latter being kept cold, and the process being continued until the bubbles of gas pass through the solution undiminished in size. The product should be kept in a stoppered bottle in a cool place.

Characters and Tests. - A colourless liquid with a pungent sulphurous odour. Specific gravity 1.04. It gives no precipitate, or but a very slight one, with Chloride of Barium, but a copious one if solution of Chlorine be also added. 34.7 grains by weight of it mixed with an ounce of distilled water and a little mucilage of Starch do not acquire a permanent blue colour with the volumetric solution of Iodine until 1,000 grain measures of the latter have been added. When evaporated it leaves no residue.

No proving has yet been made, but its use has been fully commented on in B. J. H. and M. H. R

Preparation. - The above may be considered as the 1x attenuation; dilute alcohol may be used for 1, and rectified spirit for all above.