Vinegar, as prepared in this country, from malt, should be of a pale brown colour, perfectly transparent, of a pleasant, somewhat pungent, acid taste, and fragrant odour, but without any acrimony. From the mucilaginous impurities which malt vinegar always contains, it is apt, on exposure to air, to become turbid and ropy, and at last vapid. The inconvenience is best obviated by keeping the vinegar in bottles completely filled and well corked; and it is of advantage to boil it in the bottles a few minutes before they are corked.

Vinegar is sometimes largely adulterated with sulphuric acid, to give it more acidity. The presence of this acid is detected, if, on the addition of a solution of acetate of barytes, a white precipitate is formed, which is insoluble in nitric acid, after having been made red-hot in the fire. (See p. 159.) With the same intention, of making the vinegar appear stronger, different acrid vegetable substances are infused in it. This fraud is difficult of detection; but when tasted with attention, the pungency of such vinegar will be found to depend rather on acrimony than acidity.Distilled vinegar, which is employed for various purposes of domestic economy, is frequently distilled, not in glass, as it ought to be, but in common stills with a pewter pipe, whence it cannot fail to acquire a metallic impregnation.

One ounce, by measure, should dissolve at least thirteen grains of white marble.

It should not form a precipitate on the addition of a solution of acetate of barytes, or of water saturated with sulphuretted hydrogen. The former circumstance shews, that it is adulterated with sulphuric acid; and the latter indicates a metal.

The metallic impregnation is best rendered obvious by sulphuretted hydrogen, in the manner stated, page 69. The distilled vinegar of commerce usually contains tin, and not lead, as has been asserted.