The use of sulphurous acid as a preservative agent in beer and wine, either in the form of soluble sulphites, liquid sulphite of lime, or sulphur fumes, is not at all recent. It is one of the oldest preservatives known. Together with other chemical preservatives its use is forbidden in France, and the German authorities include it with borax as an agent whose physiological effect is still too little known to allow of its indiscriminate use. It is also sometimes introduced into beers by the hops, which are very generally preserved by means of sulphur fumes. The Bavarian authorities allow its use in sulphuring barrels and hops, as will be seen when their method of analysis is described later. Of course the quantities brought into the beer in this way are very small.

The qualitative test, which is given by many of the books on the subject,2 viz, the reduction of the sulphur to hydric sulphide gas by means of nascent hydrogen, is entirely erroneous, as I have proved by experiments made upon the various albuminous constituents of beer with the same test. Hops (known to be free from S02), malt, and even ground barley, treated with hydrochloric acid and zinc gave a very distinct blackening of lead acetate paper in the course of fifteen minutes, and the test applied to the beers examined gave a distinct reaction in every case. I concluded from the abovedescribed experiments that the H1 S came from the sulphur contained in the albuminous bodies of the grain, which was reduced by the nascent hydrogen. Blank experiments with the reagents used gave no test for sulphur. Since I made these experiments similar conclusions were reached by M. von Klobulow,1 who found that sulphur was reduced from any of its compounds by nascent hydrogen, and so complete is this action that he has made it the basis for a new method of estimating sulphur. It was probably by this test that sulphurous acid was found in very old wines, as has been reported. The method of detecting the presence of S02 by its oxidation to H1 S04 is probably the best, and can be employed very successfully for the quantitative estimation also. There are various methods in use for affecting the oxidation, as well as for the subsequent determination of the sulphuric acid formed. In the method employed by the Paris Municipal Laboratory the beer is acidulated with sulphuric acid, and a current of pure carbonic acid gas is drawn through the liquid and then into a solution of chloride of barium mixed with iodine water. If S02 is present, a precipitate of sulphate of barium forms in the latter mixture. Other oxidizing agents may be used instead of the iodine. Wartha2 used nitrate of silver solution for a qualitative test; bichromate of potash furnishes a very convenient agent, and the solution of it may be made standard and titrated afterwards to determine the extent of oxidation. I have used permanganate of potash with very good results for a qualitative test. But probably the best method for both qualitative and quantitative determination is that used by the union of Bavarian chemists, which I have employed in testing the samples examined. It is as follows: 100cc. of the liquid to be examined are acidulated with phosphoric acid, and distilled in a stream of carbonic acid gas, and the distillate received in a flask containing 5cc. of normal iodine solution. After the first third is distilled off, the distillate, which should still contain excess of free iodine, is acidified with hydrochloric acid, heated, and barium chloride solution added. If a precipitate of more than 10 milligrams is obtained in the barium solution, the wine or beer contains sulphurous acid in excess of the legalized limit. (The allowance of 10 milligrams of barium sulphate is made to admit of the hops being sulphured.) In using this method I have found it necessary not only to have the delivery tube from the condenser dip into the iodine solution, but also to attach a mercury valve to the flask in which it is received.

1 Compt. Rend. 95, 786.

2 Konig, for instance, p. 410; Dietzsch, p. 123.

1 Zeit. Anal. Chem. 25, 155; Chem. News, 1886, 325. 2 Berichte d. Deutsch. Chem. Gcsell. 13, 657.

A few of the samples examined by this test gave a slight turbidity with barium chloride, viz: Serial Nos. 4804-6-10-13 and 14, while only one, No. 4815, gave sufficient precipitate to justify the assertion that a sulphite had been added to it. I have not been able to find any recorded instance of sulphurous acid being found in American beers.