[1]. Could not find any record of its Sp. Gr., 3.0 is assumed.

Cd CdSO4 At. Wt.
I. (112.35 can only be regarded as a preliminary experiment)
II. 1.15781 2.14776 112.35

Discussion of the Results.

These results agree fairly well with those obtained by the chloride and bromide methods. The second experiment is more trustworthy than the first. In it, we started with pure metal and the manipulations were so simple that no serious error could have been made in them. Hence it will only be necessary to consider the end-product, i.e., the cadmium sulphate. The titration showed that the sulphate was not basic owing to loss of sulphur trioxide, and after deducting the weight of the excess of sulphuric acid we must have left a weight of cadmium sulphate which is equivalent to the metal employed. The question now is, did it contain anything else and what would be its effect? Clearly the effect of water or any other impurity would be to lower the atomic weight found, hence the atomic weight must be at least as high as the experiment indicates. As the cadmium sulphate is deposited, at least the later part of it is from a strong sulphuric acid solution, it probably does not contain any water and in this case would fix a maximum value as well as the minimum value, and thus determine the atomic weight. It might be objected to the second experiment that the sulphuric acid found may have been present as SO3 and not as H2SO4 as was assumed. This seems highly improbable, and even if it were so the error introduced would be only about .03 of a unit in the atomic weight. As the first determination was found practically neutral, it does not apply to it at all. The most probable conclusion from these experiments is that the atomic weight of cadmium is about 112.35. A more thorough study of this method would have been made if time had permitted it.

The Oxide Method.

As the chloride and bromide methods and the synthesis of cadmium sulphate all lead to approximately the same high result, it seemed probable that the oxide method which had given a much lower result (Morse & Jones 112.07) must be affected by some error. Accordingly it was examined in the manner about to be described. A set of crucibles was prepared as described by Morse and Jones in their work on this method, and in the present paper under the oxalate method. After they had been heated in a nickel crucible over a blast lamp and weighed, a weighed piece of cadmium was introduced into the smaller inside crucible, and dissolved in nitric acid with the aid of heat. An equal quantity of nitric acid was added to the tare. The acid was then evaporated off, and the resulting nitrate converted into oxide exactly as has already been described under the oxalate. The first experiment was made in this way and the second one exactly like it, only the porcelain crucible used was the one which had been employed in the first determination. The glaze had been removed by the cadmium oxide of the first determination, and before using for the second one the crucible was boiled out with nitric acid, and heated to constant weight over a blast lamp as before. Determinations III, IV and V were made in the same way except that the small inner crucible was platinum instead of porcelain. All weighings were reduced to the vacuum standard on the basis of 8.54 for the Sp. Gr. of cadmium and 8.15 for the Sp. Gr of cadmium oxide and 8.4 for the brass and 21 for the platinum weights.

The results are as follows:

Cd CdO At. Wt. Cd.
I. 1.26142 1.44144 112.11
II. .99785 1.14035 112.04
Average 112.08
III. 1.11321 1.27247 111.84
IV. 1.02412 1.17054 111.91
V. 2.80966 3.21152 111.87
Average 111.87

The oxides resulting from these determinations were always tested for oxides of nitrogen, sometimes by using meta phenylene diamine and at other times by sulphanilic acid and naphthylamine sulphate, but no traces were ever found. The average of the determinations made in porcelain crucibles is 112.08. Morse and Jones obtained the same figure or, if their results are reduced to the vacuum standard, 112.06, by the same method under the same conditions. The results of the determinations made in platinum crucibles are equally constant, but their average is 111.88 being .20 of a unit lower. Therefore, more oxide is obtained when platinum crucibles are used instead of porcelain ones. In two cases the platinum crucibles were weighed at the end of the determinations after the cadmium oxide had been removed. Their weight remained unchanged. The most probable explanation of these facts seems to be that something is retained in the oxide in both cases, but that the amount is greater in the determination made in platinum crucibles than in those in which porcelain ones were employed. We should expect this, because in porcelain crucibles some of the oxide is absorbed forming a silicate, and any volatile impurity must be expelled from this part of the oxide. Not finding oxides of nitrogen, it was thought that gases probably nitrogen and oxygen might be occluded although Richards and Rogers (Amer. Chem. Jour. 15, 567.) had examined cadmium oxide prepared from the nitrate and found only a trace of gas. Accordingly two specimens of cadmium oxide obtained in the above determinations were powdered in an agate mortar and boiled with water for some time in order to remove any adhering air. They were then dissolved in dilute hydrochloric acid from which the air had been removed by boiling. A small amount of gas was found in each case but not nearly enough to account for the difference of .31 unit in the atomic weight of cadmium between 112.38 and the oxide method. In fact not more than about one sixth of the amount required was found. It may be that the powdering of the oxide and then boiling up in water may have been to severe a treatment, and that the greater part of the occluded gas escaped during these processes. It seems that there is at least some error due to occluded gases in methods involving the decomposition of cadmium nitrate to oxide, but no satisfactory idea of its magnitude could be obtained from these two experiments as carried out.

The following experiments were then made and they seem to give definite evidence not only of the existence of an error but also of its magnitude. Carbonate of cadmium was made by dissolving pure cadmium in nitric acid, adding an excess of ammonia and a small quantity of ammonium carbonate. After standing for some time the cadmium carbonate was filtered off and rejected. The filtrate was treated with an excess of ammonium carbonate and the precipitated cadmium carbonate allowed to digest in it for some time. After washing by decantation several times the carbonate was transferred to a funnel containing a porcelain filter-plate, covered with a piece of ashless filter paper of slightly larger diameter, and washed thoroughly. with water. It was then transferred to a platinum dish, care being taken to avoid contamination with filter paper and heated gently to convert it into oxide. The resulting oxide was powdered in an agate mortar, returned to the platinum dish and heated to incipient whiteness for seven hours in a muffle furnace. The temperature must not be too high, otherwise the oxide will distill readily leaving no residue. The oxide is slightly volatile at good red heat as was observed in trying to make a determinant at this temperature by the oxide method. A weighed portion of the oxide which had been prepared from the carbonate in the manner described was dissolved in a weighed porcelain crucible and the resulting nitrate converted into the oxide again by heat just as in the oxide method. This constitutes experiment I. Experiments two and three were made in exactly the same way except that a platinum crucible was used instead of a porcelain one. The results are: