308 FOOD AND FOOD ADULTERANTS. 



meiits made upoii the various albuminous constituents of beer with the 

 same test. Hops (known to be free from SO 2 ), malt, and even ground 

 barley, treated with hydrochloric acid and zinc gave a very distinct black- 

 ening 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 above-described experiments that the H 2 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 experi- 

 ments 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 SO 2 by its oxidation to H 2 

 SO 4 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 Mu- 

 nicipal 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 SO 2 is 

 present, a precipitate of sulphate of barium forms in the latter mixture. 

 Other oxidizing agents may be used instead of the iodine. Wartha 2 

 used nitrate of silver solution for a qualitative test; bichromate of pot- 

 ash furnishes a very convenient agent, and the solution of it may be 

 made standard and titrated afterwards to determine the extent of oxi- 

 dation. 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: lOOcc. 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 suljphate is made to admit of the hops being sul- 

 phured.) 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. 



'Zeit. Aiuil. Clifin. x:>, l.v.: Chem. News, l-sr,, :;.:,. 

 s Borichto d. Doutsch. Chern. Gcsell. 13, <>.">7. 



