Cider vinegar, which is recognized in this country as the type of vinegars and which the law regards as being the substance which should be furnished when vinegar is asked for, is usually made without any artificial fermentation or treatment whatever except to leave hard cider for a year or two in a barrel, trusting to the natural ferments to produce the acetification. The formation of acetic acid goes forward usually to a degree inversely proportional to the temperature to which it is subjected. In winter acetification goes forward slowly, while in summer it goes forward more rapidly. The acetic ferment gradually increases in quantity, and by agglutination forms ropy deposits which are known as "mother of vinegar." The quantity of acid formed when acetification is complete is slightly greater than that of the original alcohol. In Alwood's experiments as high as 7.1 percent of acidity was secured when acetification was complete. The sample above cited, which contained a little over 7 percent of acetic acid, was completely fermented at ordinary cellar temperatures in a little over a year.