then evaporated fully to dryness over boiling water, the number of grammes weight gained by the dish, when multiplied by ten, gives the percentage of solid residue contained in the vinegar. There are certain characteristics peculiar to the residue of a pure cider vinegar, the principal of which are the following:--It will be about 3 per cent. in weight, and never less than 2 per cent. It is always soft, viscid, of apple flavour, somewhat acid and astringent in taste. A drop of it taken up in a clean loop of platinum or of iron wire, and ignited in a colourless Bunsen gas-lamp flame, imparts to it the pale lilac colour of a pure potash salt, without any yellow, due to sodium, being visible. The ignited residue left in the loop of wire will be a fusible bead of quite a good size, and it will have a strong alkaline reaction upon moistened test-paper, effervescing briskly when immersed in an acid. The presence in a vinegar of the _slightest_ trace of any free mineral acid will prevent the ignited residue having any alkaline reaction, or effervescing with acids. The presence of any practical amount of commercial acetic acid added to “tone up” the strength of the vinegar will cause the igniting residue to impart another colour to the Bunsen flame, and the residue itself will have a smoky pyroligneous taste or odour. Any corn glucose used in the vinegar will cause its residue when ignited to emit the characteristic odour of burning corn, and, as the last spark glows through the carbonised mass, to usually emit the familiar garlic odour of arsenic, for the common oil of vitriol usually used in the production of glucose is now mostly derived from pyrites, which almost always contain arsenic. A glucose vinegar which has been made without vaporising the alcohol after the fermentation of the glucose will also have a strong reducing action upon a copper salt in an alkaline solution, and also will give a heavy precipitation of lime with ammonium oxalate. A true malt vinegar always contains phosphates, and a wine vinegar cream of tartar. The presence of any acrid vegetable substance in a vinegar is known by the residue having a pungent taste, especially if before the evaporation the vinegar has been exactly neutralised with soda.