Several samples of so-called “beer preservatives” examined by the author, consisted of a solution of sodium salicylate and borax, dissolved in glycerine. Salicylic acid is employed in order to prevent fermentation in beer, which is exposed to great variations in temperature. Its presence is detected by the following process, suggested by Röse,[78] which is equally applicable to wine:--The beer (or wine) is acidulated with sulphuric acid, and well shaken with its own volume of a mixture of equal parts of ether and petroleum naphtha. After standing at rest, the ethereal layer is removed by a pipette, and evaporated or distilled until reduced to a few c.c. A little water and a few drops of a dilute ferric chloride solution are then added, and the liquid filtered: in presence of salicylic acid, the filtrate will exhibit a violet colour. In the case of wines, where the presence of tannic acid might interfere with the salicylic acid reaction, the filtrate is re-acidulated, then diluted, and the treatment with the ether mixture and iron chloride repeated. The second residue will now show the violet coloration, even in wines rich in tannin, and containing but 0·2 milligramme of salicylic acid per litre. The tannin can also be removed by precipitation with gelatine, and the colour test for salicylic acid subsequently applied. Glycerine is likewise sometimes used as a preservative of beer, and is also added to render the liquor richer in appearance, by communicating a viscosity to the froth which causes it to adhere longer to the sides of the glass. It can be quantitatively estimated by evaporating 100 c.c. of the sample in a capsule at a temperature of 75°, until the carbonic acid has been expelled, then adding about 5 grammes of magnesium hydroxide, and thoroughly stirring the mixture until it forms a homogeneous, semifluid mass. The contents of the dish are allowed to cool, and are then well digested with 50 c.c. of absolute alcohol, and the fluid portion afterwards separated by decantation, the residual mass being again treated with 20 c.c. of absolute alcohol, and the alcoholic solution thus obtained added to the first. The malose, parapeptone, etc., present in the solution are now precipitated by adding (with constant stirring) 300 c.c. of anhydrous ether, after which the liquid is filtered, and the filtrate concentrated, at first by spontaneous evaporation, subsequently by heating over the water-bath, until it assumes the consistency of a syrup, when it is placed in an exsiccator which connects with an air-pump, where it is allowed to remain for twenty-four hours. The syrupy residue is then digested with 20 c.c. of absolute alcohol and filtered, the filtrate being collected in a tared capsule, which is again exposed to the heat of the water-bath, and allowed to remain in the exsiccator for twelve hours, after which it is weighed. The increase in weight gives approximately the amount of glycerine contained in the beer examined.[79]