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3.1044 grammes gallium ammonium alum, upon ignition, left .5885 grm. Ga203.

Hence Ga 68.071. If O=16, Ga= 68.233.

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.4481 grammes gallium, converted into nitrate and ignited, gave .6024 grm. Ga2O3.

Hence Ga= 69.538.

69.538. If O

=

16, Ga = 69.693.

These values, assigned equal weight, give these means: If O = 15.9633, Ga= 68.854. If O = 16, Ga = 68.963.

In brief, for all practical purposes, 69 may be assumed as the atomic weight of gallium.

INDIUM.

Reich and Richter, the discoverers of indium, were also the first to determine its atomic weight.* They dissolved weighed quantities of the metal in nitric acid, precipitated the solution with ammonia, ignited the precipitate, and ascertained its weight. Two experiments were made, as follows:

.5135 grm. indium gave .6243 grm. In2O3.

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Hence, in mean, In = 110.61, if O= 16; a value known now to be too low.

An unweighed quantity of fresh, moist indium sulphide was also dissolved in nitric acid, yielding, on precipitation, .2105 grm. In,, and .542 grm. BaSO.

Hence, with BaSO, = 233, In

=

111.544; also too low.

Soon after the publication of Reich and Richter's paper the subject was taken up by Winkler.† He dissolved indium in nitric acid, evaporated to dryness, ignited the residue, and weighed the oxide thus obtained.

* Journ. für Prakt. Chem., 92, 484.

† Journ. für Prakt. Chem., 94, 8.

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In a later paper by Winkler* better results were obtained. Two methods were employed. First, metallic indium was placed in a solution of pure, neutral, sodio-auric chloride, and the amount of gold precipitated was weighed. I give the weighings and, in a third column, the amount of indium proportional to 100 parts of gold:

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Hence, if Au == 196.155,.095, In 113.417, ± .074.

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Winkler also repeated his earlier process, converting indium into oxide by solution in nitric acid and ignition of the residue. An additional experiment, the third as given below, was made after the method of Reich and Richter. The third column gives the percentage of In in In‚0 ̧: Per cent., 82.550

1.124 grm. In gave 1.3616 grm. InО ̧.

2 3

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These figures were confirmed by a single experiment of Bunsen's, published simultaneously with the specific heat determinations which showed that the oxide of indium was In2O,, and not InO as had been previously supposed :

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1.0592 grm. In gave 1.2825 grm. In,О ̧. Per cent. In, 82.589

For convenience we may add this figure in with Winkler's series, which gives us a mean percentage of In in In, 0, of 82.564, .0082. Hence, if O= 15.9633, .0035, In = 113.385,.060.

* Journ. für Prakt. Chem., 102, 282.

† Poggend. Annal., 141, 28.

Combining results, we have the following general mean:

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Although cerium was discovered almost at the beginning of the present century, its atomic weight was not properly determined until after the discovery of lanthanum and didymium by Mosander. In 1842 the investigation was 'undertaken by Beringer,* who employed several methods. His cerium salts, however, were all rose-colored, and therefore were not wholly free from didymium; and his results are further affected by a negligence on his part to fully describe his analytical processes.

First, a neutral solution of cerium chloride was prepared by dissolving the carbonate in hydrochloric acid. This gave weights of ceroso-ceric oxide and silver chloride as follows. The third column shows the amount of CeO, proportional to 100 parts of AgCl:

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The analysis of the dry cerium sulphate gave results as follows. In a fourth column I show the amount of CeO, proportional to 100 parts of BaSO:

* Ann. Chem. Pharm., 42, 134.

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Beringer also gives a single analysis of the formate and the results of one conversion of the sulphide into oxide. The figures are, however, not valuable enough to cite.

The foregoing data involve one variation from Beringer's paper. Where I put CeO, as found he puts Ce,O,. The latter is plainly inadmissible, although the atomic weights calculated from it agree curiously well with some other determinations. For instance, in the chloride series, the assumption of Ce, O, as the formula of the oxide obtained, gives Ce 137.749, while CeO, makes Ce = 141.636. The former agrees with the results of Wolf, Wing, and others quite fairly; the latter is near the value obtained by Bührig. Obviously, the presence of didymium in the salts analyzed should tend to raise rather than to lower the apparent atomic weight of cerium.

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Shortly after Beringer, Hermann* published the results. of one experiment. 23.532 grm. of anhydrous cerium sulphate gave 29.160 grm. of BaSO4. Hence 100 parts of the sulphate correspond to 123.926 of BaSO..

In 1848 similar figures were published by Marignac,† who found the following amounts of BaSO, proportional to 100 of dry cerium sulphate:

122.68

122.00

122.51

Mean, 122.40, .138

If we give Hermann's single result the weight of one experiment in this series, and combine, we get a mean value of 123.019,

.113.

* Journ. für Prakt. Chem., 30, 185. 1843.

† Arch. des Sciences Phys. et Nat., (1,) 8, 273. 1848.

Still another method was employed by Marignac. A definite mixture was made of solutions of cerium sulphate and barium chloride. To this were added, volumetrically, solutions of each salt successively, until equilibrium was attained. The figures published give maxima and minima for the BaCl, proportional to each lot of Ce2(SO4)3. In another column, using the mean value for BaCl, in each case, I put the ratio between 100 parts of this salt and the equivalent quantity of sulphate. The latter compound was several times recrystallized:

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Omitting the valueless experiments of Kjerulf,* we come next to the figures published by Bunsen and Jegel† in 1858. From the air dried sulphate of cerium the metal was precipitated as oxalate, which, ignited, gave CeO2. In the filtrate from the oxalate the sulphuric acid was estimated as BaSO4:

1.5726 grm. sulphate gave .7899 grm. CeO, and 1.6185 grm. BaSO. 1.6967

66

.8504

66

1.7500

66

Hence, for 100 parts BaSO4, the CeO, is as follows:

48.804 48.575

Mean, 48.689, ± .077

One experiment was also made upon the oxalate : .3530 grm. oxalate gave .1913 CeO, and .0506 H2O.

Hence, in the dry salt, we have 63.261 per cent. of CeO2.

* Ann. Chem. Pharm., 87, 12.
† Ann. Chem. Pharm., 105, 45.

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