whether the 50 cc. solution is evaporated to dryness and dissolved in 50 cc. of 10 per cent. citrate (20.69 cc.) or 25 cc. of solution are treated with 25 cc. of 20 per cent. citrate, and the solution allowed to stand sixteen hours (20.62 cc.). No. 6 in this series, as well as No. 7 in Series B, shows that the same result is not reached when dissolving the solid salt in citrate (B7= 21.90) and titrating as when evaporating to dryness, and redissolving in the same amount of citrate (B 6 21.62). Commercial alum is evidently not a homogeneous body, and further combination between the alumina or basic sulphate and the sulphuric acid takes place after solution in water. The analytical method as finally worked out is as follows: Dissolve 3 grams of alum in 100 cc. of water. Take 25 cc. sample, add 50 cc. strictly neutral 10 per cent. potassium-sodium tartrate and titrate with fifth-normal barium hydroxide, using phenolphthaleïn as indicator. This is equivalent to the sulphuric acid combined with the alumina plus the free acid. Evaporate a duplicate 25 cc. sample to dryness on the water-bath, dissolve in 50 cc. strictly neutral 10 per cent. sodium citrate, allow to stand ten minutes and titrate with barium hydroxide, with phenolphthalein indicator as before. The difference between these results is equivalent to one-third of the sulphuric acid combined with the alumina and hence to one-third of the alumina. The barium hydroxide solution should be standardized by a blank determination upon a solution of sulphuric acid in which approximately enough precipitated aluminum hydroxide has been dissolved to correspond to aluminum sulphate. The aluminum hydroxide may be best made by precipitation of the chloride to insure absence of sulphate. Caustic soda, even when freed from carbon dioxide by barium hydroxide, does not give such satisfactory results as the barium hydroxide. As examples of the practicability of the method the following results on two widely differing alums are cited. Alum B, a C. P. aluminum sulphate: 30 grams per liter (25 cc.) sample=0.750 gram sample. 10.90 X 3 = 32.70 cc. fifth-normal barium hydroxide equals total sulphur trioxide theoretically necessary to combine with alumina, and therefore equals alumina. 32.70 X 0.003407=0.1114 gram alumina equals 14.86 per cent. alumina. Alumina determined gravimetrically equals 14.73 and 14.80. The close agreement between the figures 32.52 cc. (free and combined sulphur trioxide) and 32.70 cc. (combined sulphur trioxide) show that the alum is almost exactly neutral with an excess equal to 0.18 cc. of fifth-normal alumina. Alum C, a commercial aluminum sulphate: 30 grams per liter (25 cc.) sample = 0.750 gram sample. 12.90 X 338.70 cc. fifth-normal barium hydroxide equals total sulphur trioxide theoretically necessary to combine with alumina and therefore equals alumina. 38.70 X 0.003407 = 0.1318 gram alumina equals 17.58 per cent, alumina. Alumina determined gravimetrically equals 17.57 and 17.50. 38.70 33.595.11 cc. fifth-normal alumina equals 0.0174 gram alumina equals 2.32 per cent. alumina more than is sufficient to form aluminum sulphate. Alum B, as shown by the above figures, is slightly basic, but a determination of free acid by the method of Beilstein and Grosset' gave 0.9 per cent free acid. This method of Beilstein and Grosset has been investigated by V. Keler and Lunge,' who state that it gives results which are uniformly slightly high but otherwise very accurate, and it therefore became necessary to explain the discrepancy. The method of Beilstein and Grosset is as follows: Dissolve 1 or grams of alum in 5 cc. of cold water, add 5 cc. of a cold, saturated solution of ammonium sulphate, allow to stand, with frequent stirring, for fifteen minutes, and then add 50 cc. 95 per cent. alcohol. Filter, wash with 50 cc. 95 per cent. alcohol, evaporate to dryness on water-bath, dissolve in water, and titrate with tenth-normal potassium hydroxide, using litmus as indicator. All the alum is, in this process, supposed to be precipitated as normal ammonium alum together with most of the excess ammonium sulphate, and the free sulphuric acid re 1 Bulletin de l'Academie Imperiale des Sciences in St. Petersburg, 1890, p. 147. 2 Zlschr. angew. Chem. (1894), p. 669. mains in solution together with a small amount of ammonium sulphate. Three determinations of free acid in alum B by this method gave 0.86, 0.88, and 0.89 per cent. free acid as sulphur trioxide-as good an agreement as could be desired. To test whether an error in Beilstein and Grosset's method due to hydrolysis might not be responsible for this apparent free acid, variations were made in amount of water and concentration of sulphur trioxide, with the following results : The Blank determinations showed that the change in results was not due to impurities in the ammonium sulphate or alcohol. results show that the decrease in the relative amount of water decreases the apparent amount of free acid, but although hydrolysis does thus play a part in influencing the results, there remains as the lowest figure, o.6 per cent., which can hardly be attributed to an error in the method. Turning back to the series of results obtained by titrating alum B in presence of citrate, it was remarked that the figures obtained by dissolving the alum directly in citrate were higher than those obtained by dissolving the alum in water, then evaporating to dryness and redissolving in citrate which showed a greater amount of free acid in the original alum than after evaporation to dryness. If the results in B 7 are taken and calculation made we find that there are required Fifth-normal barium hydroxide for tartrate titration... 10.62 X 3 = 31.86 cc. 32.52 CC. ..... 32.52 21.90 10.62 Difference.... 31.86 = 0.66 cc. = 0.70 per cent. free acid as sulphur troxide. This result is in fair accord with the results obtained by the Beilstein and Grosset method of direct estimation, and probably corresponds closely to the amount of free acid actually present in the solid salt. It is entirely incorrect, however, to hold that the solution of this alum wll have that amount of free acid, as the results on p. 463 show that the amount of alumina in solution is slightly greater than the amount necessary to form the normal salt. The solid salt is evidently not uniform. When dissolved in water to dilute solution, these inequalities disappear quickly. In concentrated solution, as in the Beilstein and Grosset method or when the salt is dissolved in citrate, equilibrium is attained much more slowly, and a titration of such a solution soon after solution is complete gives approximately the conditions prevailing in the solid salt. If the solution is allowed to stand a sufficient length of time, equilibrium is finally reached as shown by experiments C 3 and C 5, on page 461. SUMMARY. If a solution of an alum to which has been added neutral potassium sodium tartrate (Rochelle salt) is titrated with barium hydroxide, the barium hydroxide used will correspond to the sulphuric acid combined with the alumina plus the free acid. The sulphuric acid combined with sodium or potassium is not estimated. If a duplicate solution of alum is evaporated to dryness, redissolved in neutral sodium citrate and titrated with barium. hydroxide, a smaller quantity of barium hydroxide is required, and the difference between the amounts of barium hydroxide used in the two titrations is equivalent to one-third of the alumina. From these two titrations can be calculated the alumina and the sulphuric acid combined with it whether the alum be basic or acid, and if the alum is acid, the excess of acid over that necessary to form the normal sulphate. Commercial aluminum sulphate may, in its solid state, carry free acid, although in the solution such uncombined acid may disappear, combining with what had been basic portions of the solid salt. Such free acid may be estimated by dissolving the solid salt directly in citrate and titrating with barium hydroxide at once. This method gives results closely concordant with Beilstein and Grosset's method, but it does not show that the alum contains more acid than is sufficient to form with the alumina the normal salt. When aluminum sulphate is titrated with barium hydroxide thus, in presence of neutral alkali tartrate or citrate, the precipitation of barium sulphate is retarded for a time, varying from a few minutes to several hours and when the precipitate does form it is in a very peculiar colloidal form which is undergoing further investigation. Consideration of this subject and also of the action of salts of other metals than aluminum and salts of other acids than tartaric and citric, as well as the theoretical points involved are reserved for a following paper. ANN ARBOR, MICH., THE ANALYTICAL CONSTANTS OF NEATSFOOT, TALLOW AND HORSE OILS. OF BY AUGUSTUS H. GILL AND ALLAN W. ROWE. F the commonly occurring oils, fewer data are to be found about these three than about any of the others; this work was undertaken to supply this need. The various tests were applied as described in a book published by one of us; that is, the specific gravity was taken with a correct Westphal balance at 15° C. or 100° C.; the Valenta test was done with an equal quantity of glacial acetic acid, proved to be 100 per cent. by titration; the Maumené test was performed with 100 per cent. sulphuric acid, its strength also determined by titration, in a jacketed beaker, the acid being run into the oil drop by drop from a burette; the iodine number, with the solutions after having been mixed twenty-four hours, and the oils allowed to stand for four hours with it. The titer test was carried out as prescribed by Lewkowitsch, the acid being melted in a 5" testtube held in a 100 cc. round-bottomed flask. The results given are usually the average of two closely agreeing determinations. The oils used were obtained from different dealers and guaranteed pure. The constants are as follows: °C. Sp. gr. Valenta. Maumené. Sp. temp. Iodine. Titer test. Iodine No reaction. No. fatty acid Neatsfoot oil, 1. 0.915 87.9 72.9 19-20 68.6 |