of Pelouze. I subjoin Pierre's weighings, and add, in a third column, the ratio of TiCl, to 100 parts of silver:

It will be seen that the first three of these results agree well with each other and are much higher than the remaining six. The last four experiments were made purposely with tubes which had been previously opened, in order to determine the cause of the discrepancy. According to Pierre, the opening of a tube of titanium chloride admits a trace of atmospheric moisture. This causes a deposit of titanic acid near the mouth of the tube, and liberates hydrochloric acid. The latter gas being heavy, a part of it falls back into the tube, so that the remaining chloride is richer in chlorine and poorer in titanium than it should be. Hence, upon titration, too low figures for the atomic weight of titanium are obtained. Pierre accordingly rejects all but the first three of the above estimations:

The memoir of Pierre upon the atomic weight of titanium was soon followed by a paper from Demoly,* who obtained much higher results. He also started out from titanic chloride, which was prepared from rutile. The latter substance was found to contain 1.8 per cent. of silica; whence Demoly inferred that the TiCl, investigated by Rose and by Pierre

* Ann. Chem. Pharm., 72, 214. 1849. Berz. Jahresb., 30, 58.

3

might have been contaminated with SiCl,, an impurity which would lower the value deduced for the atomic weight under consideration. Accordingly, in order to eliminate all such possible impurities, this process was resorted to: the chloride, after rectification over mercury and potassium, was acted upon by dry ammonia, whereupon the compound TiCl,.4NH, was deposited as a white powder. This was ignited in dry ammonia gas, and the residue, by means of chlorine, was reconverted into titanic chloride, which was again repeatedly rectified over mercury, potassium, and potassium amalgam. The product boiled steadily at 135°. This chloride, after weighing in a glass bulb, was decomposed by water, the titanic acid was precipitated by ammonia, and the chlorine was estimated in the filtrate as silver chloride. Three analyses were performed, yielding the following results. I give the actual weighings:

1.470 grm. TiCl, gave 4.241 grm. AgCl and .565 grm. TiO2.

The "801" in the last column is certainly a misprint for .901. Assuming this correction, the results may be given in three ratios, thus:

These three ratios give three widely divergent values for

the atomic weight of titaniun;

The value assumed by Demoly is 56; who employs but

one ratio and ignores practically the others.

Upon comparing Demoly's figures with those obtained by Rose, certain points of similarity are plainly to be noted. Both sets of results were reached by essentially the same method; and in both the discordance between the percentages of titanic acid and of silver chloride is glaring. This discordance can rationally be accounted for by assuming that the titanic chloride was in neither case absolutely what it purported to be; that, in brief, it must have contained impurities; such for example as hydrochloric acid, as shown in the experiments of Pierre, or possibly traces of oxychlorides. Considerations of this kind also throw doubt upon the results attained by Pierre, for he neglected the direct estimation of the titanic acid altogether, thus leaving us without means for correctly judging as to the character of his material. In fact, not one of the determinations of the atomic weight of titanium can be regarded as trustworthy. All depend upon the chloride, and the volatile chlorides of metals are as a class especially liable to contaminations of a kind most difficult to recognize. Possibly a series of good determinations might be based upon analyses of some of the titanofluorides. I subjoin a combination of the foregoing mean values, feeling that such a general average is a little better than any one set of determinations taken singly:

This mean agrees with the average of all of Pierre's ex

periments.

ZIRCONIUM.

The atomic weight of zirconium has been determined by Berzelius, by Hermann, and by Marignac. Berzelius* ignited the neutral sulphate, and thus ascertained the ratio in it between the ZrO, and the SO,. Putting SO, at 100, he gives the following proportional quantities of ZrO2:

89.255,.039; or, if O 16, then Zr=

=

=

Hermann's estimate of the atomic weight of zirconium was based upon analyses of the chloride, concerning which he gives no details or weighings. From sublimed zirconium chloride he finds Zr 831.8, when O= 100; and from two lots of the basic chloride 2ZrOC1,.9H,O, Zr = 835.65 and 851.40 respectively. The mean of all three is 839.62; whence, with modern formulæ and O= 15.9633, Zr becomes = 89.354.

Marignac's results were obtained by analyzing the double fluoride of zirconium and potassium. His weights are as follows:

1.000 grm. gave .431 grm. ZrO, and .613 grm. K2SO.

These figures give us three ratios. A, the ZrO, from 100

Poggend. Annal., 4, 126. 1825.
Journ. für Prakt. Chem., 31, 77.
Ann. Chim. Phys., (3,) 60, 270.

Berz. Jahresb., 25, 147.
1860.

parts of salt; B, the K,SO, from 100 parts of salt; and C, the ZrO, proportional to 100 parts of K,SO:

2

Combining with Berzelius' work we get this result:

These figures need little criticism. They show conclusively that the atomic weight of zirconium ought to be redetermined. Probably the method employed by Berzelius was the best with respect to manipulation, while on the other hand it is likely that Marignac worked with purer material. Hermann's experiments could hardly have yielded certain results, since the zirconium chloride might so easily become contaminated with traces of moisture and thence of oxygen.