bisulfide and separated from this solution with gasoline. This treatment has the double effect of removing the free bromine more exhaustively and converting the precipitate into a stable crystallized form. The crystals are oxidized with nitric acid in the original vessel in which they were precipitated. A sufficient, measured amount of standard silver nitrate solution is added and the mixture gently heated. The nitric acid has to be replaced from time to time, and the manipulation continued

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... l the bromine is all combined as silver bromide. The excess of silver nitrate is titrated back by Volhard's well known method with ammonium thiocyanate. The formula C"H"Br, forms the basis for the calcu1a:ion of pure rubber, four bromines corresponding to one caoutchouc, C"H". In applying the method it is preferable t o extract the sample first with acetone and eventually with alcoholic potash to remove completely the resins which might prove a disturbing factor by forming insoluble bromine compounds. Spence has only recently demonstrated by his investigations on rubberproteins and their behavior towards bromine that the amount of the latter added to the tetrabromide in Budde's method is too small to materially influence the final results, provided the tetrabromide is calculated from the amount of bromine contained in the precipitate. The same author observed a regular loss of bromine when oxidizing the *tetrabromide with nitric acid as proposed by Budde, a fact which was confirmed by Hinrichsen and Kindscher. They therefore suggested t o replace the oxidizing and titrating process by a combustion in a current of oxygen or fusion with sodium-potassium-carbonate and potassium-nitrate mixture. The fusion method has been improved and more fully described by Spence who obtained satisfactory results. Budde's method, therefore, gives in the case of raw rubber, even a t its present stage a fair idea as to the amount of rubber contained in a given sample. A more difficult problem faces the chemist in the case of vulcanized goods. The question, "What reactions take place during the bromination?" %ecomes more complicated and the composition of the products is a matter of great uncertainty ; the method is, therefore, practically valueless for the estimation of pure rubber in cured goods. Attempts to solve this problem were made by two different investigators. Axelrod precipitated the tetrabromide from a solution in kerosene with Budde's bromination mixture. The precipitate was washed in the same way as b y Budde, and dried a t from 50 to 60' C.; after weighing, it was ignited and the ash deducted. By analyzing a number of compounds of known composition he established a factor for the calculation of pure rubber from the bromo-sulfo compound. A moment's thought will a t once reveal that such a determination is hardly applicable for general use. All sulfur of vulcanization is included in the bromine precipitate, and, as the coefficient of vulcanization is subject to considerable variation, it follows necessarily that the composition of the bromo-sulfur compound of rubber will be just as a proper theory of vulcanization, no means to judge what reactions take place and what compounds result when cured rubber is brominated. If the sulfur of vulcanization is combined chemically with the rubber molecule, there is, of course, no room left for an addition of bromine to the double linkages which are saturated with sulfur. Huebener took this question into consideration, and, by adopting the Weber-Ditmar theory of vulcanization, concluded the reaction product of bromine and vulcanized rubber consisted of three distinct compounds: tetrabromide, dibromomonosulfide. and disulfide. For purposes of calculation it is necessary to consider only tetrabromide and disulfide because two molecules of dibromomonosulfide are equal to one molecule of tetrabromide and one molecule of disulfide. Therefore, not only bromine but also sulfur of vulcanization has to be determined to find the equivalents for pure rubber, He proposed at the same time a somewhat simplified method, originally designed for hard rubber, which has the advantage of eliminating the often very troublesome and long proposition of dissolving the rubber. The sample is finely rasped and brominated with elementary bromine under water. The results obtained in our laboratory have been invariably high, as it seems practically impossible to free the precipitate from the excess of bromine by a simple washing with hot water. Of course I have to admit that we have not made an exhaustive study of the subject and therefore are not ready to condemn the method as valueless. Even if all methods, as described before, have failed to be satisfactory to everybody and in every instance, their development marks a decided progress in rubber chemistry. It can be justly hoped that a t a not too far distant time chemists will be able t o submit such methods of analysis as will be acceptable to both the merchant and the manufacturer. The importance of this problem was recognized a t the International Rubber Exhibition at London when for the first time the International Testing Committee met in full session to discuss the questions which should be settled by this body.