On the composition of chloride of barium

Abstract

The frequent employment of chloride of barium in delicate chemi­cal investigations, renders an exact knowledge of its composition pe­culiarly desirable ; and this has become a more important object of inquiry since it has been made by Dr. Thomson the basis of his calcu­lations of the chemical equivalents of sulphuric acid, and of thirteen metals and their protoxides. He has deduced from his experiments with the chloride of barium the number 36 as the equivalent of chlorine ; 70 as that of barium; and 78 as that of baryta; whence the equivalent of the chloride of barium would be 106 ; and accord­ingly, on mixing this quantity of the chloride with 88 parts of sul­phate of potash, each being previously dissolved in separate portions of distilled water, he finds a complete double decomposition has taken place ; the resulting sulphate of baryta, reduced to dryness, weigh­ing 118 parts, and the muriate of potash yielding 76 parts of chlo­ride of potassium. Hence he infers that 40 is the equivalent number for sulphuric acid, and 48 that for potash. Berzelius, however, maintained that this experiment, as well as the deductions from it, are not exact. Dr. Thomson having, in consequence of Berzelius’s objections, repeated his experiments, still asserts their accuracy. The author of the present paper investigated the subject with the greatest care, employing materials in a state of perfect purity, and obtained results which coincided with those of Berzelius. He details the pre­cautions he took for ensuring the conditions of perfect purity in the substances with which his experiments were made, and to the neglect of which he traces some of the errors which he imputes to Dr. Thomson’s analysis. But there exists also a more radical cause of error in the method employed by that chemist; for Dr. Turner finds that when solutions of muriate of baryta and of sulphate of potash are mixed together, a small portion of the latter salt adheres tenaci­ously to the sulphate of baryta, which is precipitated, and escapes decomposition. By employing different processes the author avoids this source of fallacy; first, from the chloride of barium, previously dissolved in water, he throws down sulphate of baryta by adding sulphuric acid; and, secondly, he effects a precipitation from a simi­lar solution of the chloride, by nitrate of silver, and infers the quantity of chloride from that of the fused horn-silver obtained, having pre­ viously determined, by a separate series of experiments, the exact composition of horn-silver. The conclusion he draws from his re­searches is, that 100 parts of chloride of barium correspond to 137·63 parts of the chloride of silver, which latter substance contains 34·016 parts of chlorine, and therefore leaves for the proportion of barium 65·984 parts. The real equivalent of barium, however, will depend upon that of chlorine, which is itself not yet satisfactorily de­termined.