This bell jar may by placed on the sand of a bath or better upon a ring of asbestos board on a sheet-iron pan or upon an iron plate. The object to be heated may be placed upon a tripoda triangle or such a porcelain support, with perforations for crucibles, etc., as is frequently used in desiccators.

The advantages over the ordinary copper air-bath are:

1. Cheapness. A bell jar of ten inches diameter costs less than a third as much as the copper bath of the same dimensions.

2. Cleanliness. There is no corrosion from acid fumes. Incrustations upon the sides and roof of the jar are easily seen and removed so that there is no risk of their falling back into the

dishes or casseroles. It will then be especially useful for the drying down of acid solutions in the separation of silica.

3. The operation of drying can be watched.

4. The only part requiring renewal is the iron pan or plate and either one of these is very cheap. The burning out of the copper bottom of the ordinary air-bath is of distressingly frequent occurrence.

5. Any warm plate may, by this bell jar, be turned into a drying-bath in which the temperature can be watched and

regulated by increasing the thickness of the asbestos board or by other means.

I am strongly convinced of the wide application and general usefulness of this modified drying apparatus.

UNIVERSITY OF NORTH CAROLINA.

ΤΕ

CONTRIBUTIONS TO THE CHEMISTRY OF ZIRCONIUM, No. 8.

SOME PROPERTIES OF ZIRCONIUM DIOXIDE.

BY F. P. VENABLE AND A. W. Belden.

Received February 14, 1898.

HERE are so many misstatements as to the properties of zirconia in the literature of chemistry that we think it well

to publish the results of our study of this body.

1. Specific Gravity.-The following values have been given: 4.30 (Berzelius), 4.90 (Berlin), 5.50 (Sjögren), and 5.45 (Hermann). Our determinations were made with quite pure material

and yielded as a mean 5.489.

2. Solubility. The strongly ignited zirconia is practically insoluble in all acids except hydrofluoric. In this it is readily soluble on heating. If soda is present along with the zirconia, as sodium zirconate, the mass is not dissolved, probably owing to the formation of sodium zirconium fluoride. The statement is frequently met with that zirconia is soluble in sulphuric acid. This is based upon observations of Berzelius and his directions are that the zirconia must be finely powdered and heated with a mixture of two parts sulphuric acid and one part water until the sulphuric acid volatilizes. Our experiments would show that it is quite insoluble in concentrated sulphuric acid and when the directions of Berzelius are followed out this dilute acid dissolves only 6.72 parts to the 1,000 parts of acid. Neither concentrated nor dilute hydrochloric acid nor nitric acid seem to have much action upon it.

Prolonged heating with sodium carbonate effects very little change in zirconia. It is only sparingly dissolved. Berzelius must have made use of a carbonate carrying some hydroxide in the experiments in which he speaks of dissolving the zirconia by means of sodium carbonate.

Again, half a gram of zirconia (finely powdered) was fused for nine hours with twenty grams of microcosmic salt.

The zirconia did not apparently enter into the fusion nor could the formation of crystals be observed as has been maintained. The same results were observed in a similar experiment with borax.

3. Zirconium Hydroxide.-The statement is made in Dammer's Handbook (1, 619) that of the two possible hydroxides only ZrO(OH), is known, and that, further, numerous pyrohydrates are known whose contents of water lie between this and the anhydride. This is based upon the work of G. J. Bruch,' who described a meta-zirconic acid, ZrO(OH),, prepared as a white, voluminous, almost gelatinous precipitate, by precipitating a solution of a salt of zirconium with ammonia.

In the following experiments this precipitate, gotten with ammonium hydroxide, was washed free of ammonia, then placed in a Gooch crucible and washed about twelve times with alcohol (ninety-five per cent). It was then washed with ether. After weighing the crucible it was heated strongly and the loss of water was 26.50 per cent. In a second experiment the zirconium hydroxide precipitate was pressed between filter-paper, placed in a Gooch crucible, and washed with petroleum ether until there was no further loss of weight. This washing was done in an atmosphere free from carbon dioxide. Afterwards the crucible was strongly heated. The loss of water was 26.19 per cent. A third experiment carried out in a similar manner yielded also 26.30 per cent. Other experiments gave losses of 25.97 per cent. and 27.21 per cent. The percentage of water in Zr(OH), is 22.69. It would therefore seem that treatment with petroleum ether brought the precipitate very nearly down to the composition Zr(OH),. In using alcohol and ether there seemed to be no definite limit to the removal of water and hence in several experiments final constant weights were not obtained. Two experiments gave respectively 11.11 and 9.45 per cent. of The percentage in ZrO (OH), is 12.80.

A specific gravity determination of the hydroxide containing 25.97 per cent. of water gave 3.25.

4. Solubility of the Hydroxide.-The statement of Bruch, that this substance is soluble in 5,000 parts of water and turns litmus

1 Jahresber, 1854, 729.

paper blue and turmeric paper orange-yellow is cited by several authors. This is manifestly an error. The alkaline reaction observed was doubtless due to the ammonia which it so persistently retains when ammonium hydroxide is used in the precipitation. Bailey and others have noted how prolonged the washings must be to free the hydroxide from ammonia. Experiments were carefully carried out to test this point but we failed to detect in the pure hydroxide any alkaline reaction or any appreciable solubility in pure water. Certainly it is less than the figure given by Bruch.

The solubility of the cold precipitated hydroxide in acids is as follows: It is very readily soluble in concentrated and dilute hydrochloric acid (which is the best solvent for it), in hydrofluoric acid, and in hydrobromic acid. It is very sparingly dissolved by hydriodic acid. Concentrated and dilute nitric acid dissolve it easily.

Among the organic acids it was found that oxalic acid was the best solvent, dissolving it nearly as well as the mineral acids. Saturated solutions of tartaric and citric acids dissolved less than 11,000 and glacial acetic acid also dissolved very little. If the zirconium hydroxide is precipitated from a hot solution it is much less soluble in the dilute acids. Thus dilute hydrochloric or dilute nitric acid will dissolve only about I: 100 and dilute oxalic acid dissolves only about half as much. If the precipitate, however, stands for some days in contact with the acid it is dissolved to about the same extent as when precipitated cold.

As to the solubility in basic substances, ammonia (sp. gr. 0.90) does not seem to appreciably dissolve it, but when diluted (sp. gr. o.96) there is dissolved about 1: 10,000 parts of ammonia. Clarke' has shown the solubility in potassium hydroxide, and in sodium hydroxide to be as follows:

Gram.

50 per cent. KOH solution dissolved per cc. ...... 0.00233

Certain salts of ammonia exert quite a solvent action. Thus a saturated ammonium carbonate solution will dissolve about I: 100, and a solution of ammonium tartrate rendered strongly ammoniacal has a somewhat smaller solvent action.

5. Absorption of Carbon Dioxide.-Zirconium hydroxide shows a decided tendency to absorb carbon dioxide. This may be observed on exposing the moist precipitate to the air or on prolonged heating at a low temperature (100°-150°) over an ordinary burner. Such a mass will gain very noticeably in weight. The extent of this absorption of carbon dioxide was tested as follows: About two grams of the moist hydroxide were placed in a porcelain boat in a tube and pure carbon dioxide passed over it for some twenty-five or thirty hours. At the end of this time the hydroxide had contracted into small, hard, horn-like particles and no further change was observable. Purified air was next passed over these particles for eighteen or twenty hours and the carbon dioxide coming off was caught in a barium hydroxide solution and determined. Then the particles were heated and the carbon dioxide was caught by a fresh solution of barium hydroxide. It was found that about one-third of the carbon dioxide which had been absorbed came off without heating. As no distinct point could be observed at which this carbon dioxide ceased coming off (no clear line of demarcation between that lost at ordinary temperatures and that lost on heating), no inferences were drawn and the carbon dioxide was all reported together. The percentages of carbon dioxide absorbed were 16.42, 5.72, and 7.05. These show a wide variation and can scarcely be taken as showing more than the fact that considerable amounts of the gas are absorbed with the formation of basic carbonates. The basic carbonate, Zr(CO,),. 2Zr(OH),, contains 16.68 per cent. of carbon dioxide, and Zr(CO,),.6Zr(OH), contains 7.55 per cent., and Zr(CO,),. 8Zr(OH), contains 5.96 per cent.

This experiment was varied somewhat by suspending the zirconium hydroxide in water and passing carbon dioxide through the water. This gave 6.73 and 6.00 as the percentages of carbon dioxide absorbed in two separate trials.

UNIVERSITY OF NORTH CAROLINA.