with nitric acid, the chlorine was precipitated by a known amount of silver. The figures in the third column show the quantities of BiCl, proportional to 100 parts of silver: The first three of the foregoing series of experiments were made with slightly discolored material, and may therefore be rejected. The remaining six percentages give a mean of 97.791; whence Bi 209.78; or, if O 16, Bi 210.26. = = = As between the unaccordant results of Schneider and of Dumas, those of the former chemist are probably nearest correct. His method of determination was the more reliable, and the details which he gives concerning his manipulations afford strong presumptions of accuracy. Doubtless the bismuth trichloride used by Dumas, contained, like the corresponding antimony compounds, traces of oxychloride. We may fairly assume, for all practical purposes, that the atomic weight of bismuth cannot be far from 208. TIN. Stannic oxide and stannic chloride are the compounds which have been studied in estimating the atomic weight of tin. The composition of stannic oxide has been fixed in two ways; by synthesis from the metal, and by reduction in hydrogen. For the first method we may consider the work of Berzelius, Mulder and Vlaanderen, and Dumas. * Berzelius oxidized 100 parts of tin by nitric acid, and found that 127.2 parts of SnO, were formed. The work done by Mulder and Vlaanderen † was done in connection with a long investigation into the composition of Banca tin, which was found to be almost absolutely pure. For the atomic weight determinations, however, really pure tin was taken, prepared from pure tin oxide. This metal was oxidized by nitric acid, with the following results. 100 parts of tin gave of SnO,: Dumas oxidized pure tin by nitric acid in a flask of glass. The resulting SnO, was strongly ignited, first in the flask, and afterwards in platinum. His weighings, reduced to the foregoing standard, give for dioxide from 100 parts of tin the amounts stated in the third column: 12.443 grm. Sn gave 15.820 grm. SnO2. 127.14 Mean, 127.105, ± .024 In an investigation later than that previously cited, Vlaanderen || found that when tin was oxidized in glass or porcelain vessels, and the resulting oxide ignited in them, traces of nitric acid were retained. When, on the other hand, the oxide was strongly heated in platinum, the latter was perceptibly attacked, so much so as to render the results uncertain. He therefore, in order to fix the atomic weight of tin, reduced the oxide by heating it in a porcelain boat in a stream of hydrogen. Two experiments gave Sn = 118.08, and Sn = 118.24. These, when O= 16, become, if reduced to the above common standard, * Poggend. Annal., 8, 177. Journ. für Prakt. Chem., 49, 35. 1849. ||Jahresbericht, 1858, 183. 127.103 Mean, 127.082, .012 We have now four series of results showing the quantity of SnO, formed from 100 parts of tin. To Berzelius' single value may be assigned the probable error of a single experiment in Mulder and Vlaanderen's series: Dumas, in the paper previously quoted, also gives the results of some experiments with stannic chloride, SnCl.. This was titrated with a solution containing a known weight of silver. From the weighings given, 100 parts of silver correspond to the quantities of SnCl, named in the third column: All these data properly combined give us the following values for the atomic weight of tin: TITANIUM. The earliest determinations of the atomic weight of titanium are due to Heinrich Rose.* In his first investigation he studied the conversion of titanium sulphide into titanic acid, and obtained erroneous results; later, in 1829, he published his analyses of the chloride. This compound was purified by repeated rectifications over mercury and over potassium, and was weighed in bulbs of thin glass. These were broken under water in tightly stoppered flasks; the titanic acid was precipitated by ammonia, and the chlorine was estimated as silver chloride. The following results were obtained. In a fourth column I give the TiO, in percentages referred to TiCl, as 100; and in a fifth column the quantity of TiCl, proportional to 100 parts of AgCl: 2 If we directly compare the AgCl with the TiO, we shall find 100 parts of the former proportional to the following quantities of the latter: 14.243 14.081 14.153 14.373 14.324 Mean, 14.235, ± .036 From all these figures we can get three values for Ti, thus: * Gilbert's Annalen, 1823, 67 and 129. † Poggend. Annal., 15, 145. Berz. Lehrbuch, 3, 1210. These results will be discussed further along in connection with others. Shortly after the appearance of Rose's paper, Mosander* published some figures giving the percentages of oxygen in titanium dioxide, from which a value for the atomic weight of titanium was deduced. Although no details are furnished as to experimental methods, and no actual weighings are given, I cite his percentages for whatever they may be worth: 40.814 40.825 40.610 40.180 40.107 40.050 40.780 40.660 39.830 Mean, 40.428 These figures give values for Ti ranging from 46.277 to 48.231; or, in mean, Ti = 47.045. They are not, however, sufficiently explicit to deserve any further consideration. It will be noticed that the highest value nearly coincides with Rose's lowest. In 1847 Isidor Pierre made public a series of important determinations.† Titanium chloride, free from silicon and from iron, was prepared by the action of chlorine upon a mixture of carbon with pure, artificial, titanic acid. This chloride was weighed in sealed tubes, these were broken under water, and the resulting hydrochloric acid was titrated with a standard solution of silver after the method * Berz. Jahresbericht, 10, 108. 1831. |