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striking when the perfect crystalline structure of the body is considered. I have observed a similar abnormal composition in the salt of chloride of strontian, while the salt of chloride of potassium, for example, even when crystallized in the most confused manner, has a composition agreeing completely with theory.

Reserving further discussion for another occasion, when the subject shall have been more thoroughly investigated, the following is the view which I am at present inclined to take of this, as well as of some other cases of similar nature.

The body in question may be regarded as composed of normal salt, of definite atomic constitution, to which is added a certain excess, variable in amount, of cyanide of mercury; which latter is not combined chemically with the nominal salt, but enclosed like a foreign body in the interstices of its crystalline structure. If this view be correct, the water and barium should be present in the abnormal in the same relative proportion in which they exist in the normal salt; and if the excess of cyanide of mercury be deducted from the total salt analyzed, the barium found should be in the same proportion in the residue as it is in the normal salt. The one of which conditions is virtually included in the other.

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The abnormal crystals of this salt, which I have examined, agree pretty well with these conditions. Omitting details for the present, it may be stated that the water thus calculated on the barium found is in general deficient by about 0.5 per cent; it agreed in one case very nearly with the theory, and was found once to be 0.7 per cent in excess. this case unusual and perhaps inadmissible means had been taken to remove adhering moisture. The salt is permanent in a not too dry air, but in the air of a heated room, or in air kept dry by means of sulphuric acid, it effloresces and loses at last nearly the whole of its water of crystallization. When it is considered that the only means we possess of drying such a salt without expelling the water essential to its crystalline constitution is the mechanical operation of pressure between paper, the above-mentioned deviation from theory, amounting to 6 or 7 milligrammes on the quantity taken for analysis, may not be thought to exceed the limits of the unavoidable errors of observation.

Should this view be borne out by further investigation, and should it be admitted that crystallized bodies may hold certain of their constituents, or even foreign substances, in a state not of chemical but of physical or crystallographic combination, this property would serve to explain the

apparent inexactness of certain chemical analyses, as well as facts in mineralogy which at present are not reconcilable with the laws of atomic proportion; and would show that, where a deviation from these laws is coexistent with crystalline structure, such deviation may be merely apparent, and the crystalline form in reality dependent upon the presence of a body possessed of a definite atomic constitution.

Dr. C. T. Jackson exhibited a fragment of the Dhurmsala meteorite, which had been presented to the Boston Society of Natural History by the Governor-General of India.

Mr. Safford announced the results of his calculations on the perturbations of Uranus.

Five hundred and second meeting.

January 14, 1862. MONTHLY MEETING.

The PRESIDENT in the chair.

The Corresponding Secretary read various letters relative to the exchanges of the Academy.

F. H. Storer having declined to serve on the Rumford Committee, Prof. Winlock was chosen to fill the vacancy.

The Report to the United States Government on the Physics and Dynamics of the Mississippi, by Capt. Humphries and Lieut. Abbot, of the U. S. Topographical Engineers, received by the Academy from the authors, was referred to Professor Peirce.

W. P. Dexter communicated the following paper, viz. :

Remarks upon the Recent Determinations of the Atomic Weight of Antimony.

The atomic weight of antimony has been successively investigated by Berzelius, Kessler, Schneider, H. Rose, myself, and Dumas. Very recently Kessler has revised and repeated his determinations, and arrived at a result which "completely agrees "* with that previously

* "Welches (das Atomgewicht) sich nun nach meinen späteren Versuchen als durchaus ubereinstimmend mit dem von Dexter gefundenen herausstellt." — Pogg. Ann., Bd. CXIII. S. 134.

obtained by me. I have hitherto abstained from making any remarks upon these researches, or from entering upon any defence of my own work, from the conviction that a determination of an atomic weight, if correct, would certainly be in the end received, and if incorrect, would as certainly be superseded by a better.

The equivalent found by Berzelius* was 129, when reduced to the scale on which H: = 1, and it is remarkable as being the only instance in which a grave error has been detected in the numerous determinations to which he devoted a large part of his life.

Passing over the equivalent of Berzelius, which is now admitted to be altogether too high, the other determinations may be divided into two classes; those of Schneider and H. Rose, which place the equivalent at about 120, and those of Kessler, Dumas, and myself, which give a number not varying much from 122. Kessler claims to have been the first to show the error in the equivalent which had been universally adopted on the authority of Berzelius. His earlier experiments gave 123.58 to 123.84 for the atomic weight.†

A few months later appeared the elaborate research of R. Schneider of Berlin. A native sulphide of antimony, said by him to be free from appreciable quantities of arsenic and the metals by which it is usually accompanied, served as the basis of this work. The sulphide was reduced, at a temperature just sufficient to fuse it, by a slow stream of pure hydrogen. The loss of weight, after applying small corrections for a minute quantity of quartz present, for a portion of the antimony volatilized, and for a trace of sulphur retained by the reduced metal, gave the necessary data for the calculation of the atomic weight.

It is an invidious task, especially for a fellow-laborer, to examine into the causes of error in a work so elaborately and conscientiously executed. The results show, however, and Schneider himself admits the presence of, some constant error, in consequence of which the proportion of antimony in the sulphide seemed to increase regularly with the quantity of material operated upon. So that those determinations gave the highest atomic weight in which the largest quantity of sulphide was employed. I am inclined to think that the error may have arisen in part from the action of the flame upon the glass of the

* Schweigg. Journ., Bd. VI. S. 144, and Bd. XXII. S. 69.

† Pogg. Ann., Bd. XCV. S. 204.

Ibid., Bd. XCVIII. S. 293.

tube in which the reduction was effected. It is stated by Stas,* that "all kinds of glass, when long exposed to a red heat in contact with the flame of alcohol or of gas, lose slowly, but continuously, in weight.” This loss would have apparently increased the amount of sulphur in the sulphide, and so have led to a too low valuation of the atomic weight. That this is not the only constant error is shown by the fact that those determinations gave the highest equivalent in which, the quantity of substance being the largest, the glass was longest exposed to the action of the flame.

Secondly, these experiments were made with a native sulphide of antimony; their success depended upon its purity, and upon its having the precise atomic constitution attributed to it. On the first of these points we have the opinion of Berzelius, that "native compounds are never sufficiently pure to be used in such researches." † We know by the experience of Dumas, of Erdmann and Marchand, and of Scheerer in the determination of the atomic weights of calcium and magnesium, how difficult it is to detect and make allowance for the presence of minute quantities of foreign bodies; and every one who has worked with antimony will admit that the difficulty in this case is still greater. On the subject of the precise atomic constitution of these native compounds I have long had doubts; and the paper which I recently had the honor of submitting to the Academy shows that they may not be without foundation, even when the body can be obtained in well-defined crystals.

Whatever may be thought of these doubts, which it is indeed easy to raise about the best-executed work, the fact of the dependence of the atomic weight in Schneider's experiments upon the quantity of matter operated upon, seems to me sufficient to destroy confidence in his results. I have, accordingly, not calculated the probable error of his determinations; his extreme numbers are 120.08 and 120.53, the mean of eight being 120.3.

Professor Rose's work was published rather as a confirmation of

*"Sans exception aucune, tout verre chauffé longtemps au rouge dans la flamme de l'alcool ou du gaz éclairant, diminue de poids lentement, mais constamment." - Recherches sur les Rapports Réciproques des Poids Atomiques, (Bruxelles, 1860,) p. 17.

† "Les composés naturels ne sont jamais assez purs pour être propres à des pareilles recherches." - Traité de Chimie, (Paris, 1847,) Tom. IV. p. 529.

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the equivalent obtained by Schneider, than as an independent research upon the atomic weight. He gives as trustworthy the result of but one analysis of the chloride, and that not made by himself. From this he derived the number 120.7.

Of the researches which place the atomic weight at about 122, my own * was the first in point of time, and was commenced before the publication of that of Schneider. After attempting without success to deduce the atomic weight from the quantity of gold which a known weight of antimony could precipitate, with the view of rendering as small as possible the influence of the errors of the operation upon the result, the determination was finally effected by oxidizing the pure metal by nitric acid, and ascertaining the weight of the resulting antimoniate of oxide of antimony. That this body has really the composition SbO was also proved by a separate experiment. The process, besides its simplicity and accuracy, has the advantage of giving the atomic weight directly dependent upon that of oxygen. In ten determinations the equivalent was found from 122.24 to 122.48. The most probable value is 122.33; and the probable error of the individual determinations is 0.05.

In the last edition of the Handwörterbuch der Chemie † this determination is spoken of as being not so accurate (weniger genau), by which is probably meant that it is not so correct, as that of Schneider. As no reason whatever is given for this opinion, I do not think it calls for any other remark than that the writer, H. Bolley, apparently had not read the paper which he thus criticises. For in the very next article,‡ by the same writer, the determination of chloride of antimony by means of the double chloride of gold and potassium is recommended; although this process had been thoroughly tried by me, in the hope of making it available in the determination of the atomic weight, and stated to lead to completely erroneous results. That this process had given Professor Rose apparently satisfactory results when the equivalent of antimony was taken at 129, would not generally be thought a good reason for supposing that it would give equally good ones when the equivalent was found to be only 120. In fact, Rose has since admitted in a similar case, and referring to my experiments, that the process must be abandoned. §

* Pogg. Ann., Bd. C. S. 563.

§ Pogg. Ann., Bd. CX. S. 541.

† Braunschweig, 1858. Art. Antimon., Bd. II. S. 43. Art. Antimon., Bestimmung und Trennung, S. 56.

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