CHEMISTRY. 



93 



peculiar differences in the behavior of fluo- 

 rine in entering into combination with other 

 elements. The analogies of fluorine with the 

 halogens on the one hand, and with oxygen 

 on the other hand, have often been remarked 

 upon. The compounds of fluorine generally 

 bear resemblance to compounds of chlorine, 

 but some striking differences in the character 

 of these compounds have also forced themselves 

 upon the attention ; and the tendency of the 

 fluorides to the formation of double salts, with 

 formulas analogous to those of oxygen com- 

 pounds, and the formation of salts including 

 both oxygen and fluorine, has suggested that 

 some close natural relation may exist between 

 these elements themselves. There has, there- 

 fore, been ground for questioning whether fluo- 

 rine should be classed with chlorine among the 

 monad elements, with the formula HF to rep- 

 resent hydrofluoric acid, and assigned an atom- 

 ic weight of 19, or with oxygen among the 

 dyads, with the formula HVF for hydrofluoric 

 acid, and an atomic weight of 38. Professor 

 Mallet's experiments bore a special reference to 

 this question. The result was such as to justify 

 the assumption that at the temperature of 30 

 centigrade the molecule of hydrofluoric-acid 

 vapor should be represented, not as HF, but 

 as H a F 2 , while at higher temperatures disso- 

 ciation takes place, leading to the production 

 of diatomic molecules of HF. The structure 

 of the molecule of double weight, HuFa, maybe 

 regarded as resulting from fluorine behaving 

 not only as a monad, but also as a triad, and 

 acting in double atoms like those of nitrogen 

 in the di-azotic compounds. In such a condi- 

 tion the element presents a pseudo-dyad char- 

 acter, and becomes capable of replacing oxy- 

 gen and of manifesting the linking function of 

 that element. This assumption, supported by 

 the experimental evidence brought forward by 

 Professor Mallet, may serve conveniently to ex- 

 plain the composition of a number of fluorine 

 compounds, whose formulas are difficult to 

 write in a satisfactory way if fluorine be con- 

 sidered exclusively monad. 



Atomic Weight of Platinum. The group of 

 metals embracing osmium, iridium, and plati- 

 num has until recently exhibited a series of 

 irregularities in that their atomic weights did 

 not manifest those relations to each other 

 which their properties, in connection with 

 Meyer and Mendelejeff's theory of classification, 

 indicated they should bear. Dr. K. Seubert, 

 two years ago, undertook the revision of the 

 atomic weight of iridium, and fixed it at 192'- 

 644, putting it below that of platinum. He 

 has since fixed the atomic weight of platinum 

 at 194-177, giving it the place above that of 

 iridiura and below that of gold, which the 

 theory requires it should occupy, while the 

 previous estimation of its atomic weight made 

 it above that of gold. The ascending series, 

 iridium, platinum, gold, is now, as to those 

 three metals, agreeable to theory ; but osmium 

 still occupies an anomalous position, its re- 



ceived atomic weight, 198'5, being above that 

 of gold, while the theory requires that it should 

 be below that of iridium. 



Molecular Weights of Decipium and Sama- 

 rium. M. Delafontaine, in 1878, described an 

 earth having a molecular weight of about 122, 

 which he had obtained from samarskite, and 

 which he called decipia, regarding it as an oxide 

 of a new metal, decipium. He has continued his 

 studies of this substance, and has been brought 

 to regard it as a mixture of two oxides, one of 

 them having a molecular weight of about 130, 

 and the other a lower molecular weight. The 

 former substance gives no absorption spectrum, 

 while the second gives the spectrum which 

 M. Delafontaine described in 1878 as that of 

 decipia. M. Lecoq has also announced the 

 discovery of a new metal in samarskite, cor- 

 responding with the second substance detected 

 by M. Delafontaine, to which the latter pro- 

 poses to give the name of samarium. The mo- 

 lecular weight of its oxide is believed t<> be less 

 than 117. Samaria appears to be identical 

 with the earth Y/3, having a molecular weight 

 of 115, which M. Marignac has found in sam- 

 arskite, while that chemist's Ya, having a mo- 

 lecular weight of 120'5, may be supposed to be 

 a mixture of decipia and terbia. 



Atomic Weight of Aluminum. Professor J. 

 W. Mallet, considering that the estimation of 

 the atomic weight of aluminum was resting on 

 an insufficient basis of accurate experiment, 

 has pursued, during three years, a course of 

 experiments for the revision of the determina- 

 tion, in which he has kept in view the princi- 

 ples 1. That each process used should be as 

 simple as possible, and should involve as little 

 as possible of known liability to error ; 2. That 

 different and independent processes should be 

 resorted to as the means of checking each 

 other's results; 3. That each process should 

 be carried out with quantities of material dif- 

 fering considerably from each other in succes- 

 sive experiments ; 4. That only such other 

 atomic weights should be involved as may be 

 counted, among those already known, with the 

 nearest approach to accuracy. Three series of 

 experiments were conducted, of which the 

 first series was based on the purification of am- 

 monium alum ; the second on the preparation 

 and purification of aluminum bromide ; and the 

 third on the preparation and application of 

 pure metallic aluminum. The mean result of 

 the twenty-five experiments which were re- 

 garded as the more accurate of the thirty that 

 were made, gives the atomic weight of alumi- 

 num as 27'02. This is believed by Professor 

 Mallet to bear in favor ot Prout's law, which 

 assumes that all the atomic weights are multi- 

 ples of that of hydrogen. 



Atomic Weight of Cadmium. Mr. Oliver 

 "W. Huntington, under the direction of Profess- 

 or J. P. Cooke, of Harvard College, has made 

 a revisionary determination of the atomic 

 weight of cadmium. He used a pure bromide 

 of cadmium, specially prepared for the pur- 



