630 SCIENTIFIC RECORD FOR 1883. 



it is found that the ratio of O to H is not constant, but varies with the 

 state of division and of saturation of the oxide, the duration of contact 

 of the water formed with the oxide and with the temperature, from 7.95 

 to 8.15. The latter value is obtained with a saturated and divided oxide 

 filling the tube ; the former, with oxide in lumps filling the tube for a 

 space of 25 centimeters. With a larger empty space the ratio has fal- 

 len to 7.90. 



Prof. Josiah P. Cooke, jr., calls attention to the fact that he expressed 

 similar views and fully worked them out more than twenty-five years 

 ago. He quotes from his paper on " Two new crystalline compounds 

 of zinc and antimony, and on the cause of the variation of composition 

 observed in their crystals," published in the Memoirs of the American 

 Academy of Arts and Sciences in 1S55 (new series, vol. v., p. 337). 

 He also refers to a paper published in the American Journal of Science 

 (second series, xx, 1855) entitled "On an apparent perturbation of the 

 law of definite proportions observed in the compounds of zinc and anti- 

 mony." In these papers the opinions now under discussion were 

 brought forward, not simply as speculations, but as a legitimate theory 

 advanced to explain the facts observed in his investigations. Professor 

 Cooke shows that as long since as 1855 he questioned the absolute 

 character of the law of definite proportions ; he then suggested that the 

 variation is due to the very weak affinity between elements manifesting 

 a fluctuating composition; and he wrote at that time, " To what extent 

 this perturbation of the law of definite proportions prevails among 

 chemical compounds future investigation must determine. There are, 

 however, a number of facts which tend to prove that it is very general 

 whenever chemical affinity is weak." Professor Cooke fully substanti- 

 ates his claim to priority, and then proceeds to consider whether the 

 progress of chemistry since 1855 has tended to confirm or to invalidate 

 these views. He says, in conclusion, that he " feels that the weight of 

 evidence is at present in favor of the atomic theory, and of that abso- 

 lute definiteness of combiuing proportions which this theory involves ; " 

 yet at the same time he " is very glad that the whole question " is 

 again open to discussion. "But, although it must be admitted that the 

 atomic theory is the only basis on which a consistent philosophy of 

 chemistry can at present be built," Professor Cooke confesses that 

 "he is rather drawn to that view of nature which refers all differences 

 between substances to dynamical causes, and which regards the atomic 

 theory as only a temporary expedient for representing the facts of 

 chemistry to the mind." (Am. J. Sci. (3), xxvr, 63 and 310.) 



Atomic Weight Determinations. 



Didymium. — Owing to the discrepancies in the existing figures for 

 the atomic weight of didymium, B. Brauner has re-examined the mh 

 ject. Cleve had previously assigned the figures 117.2, and Brauner 

 himself had found 116.58. The latter undertook experiments to decide 



