158 , Scientific Intelligence. 



and filled the vessel with its vapor. The temperature of the bath 

 and the reading of the barometer being noted, the vessel was 

 withdrawn from the bath, allowed to cool and weighed, the 

 necessary corrections being applied in calculating the result. The 

 experiments were made at temperatures varying from 26*4° 

 (which is about 7° above the boiling point of hydrogen fluoride 

 under normal pressure) to 88*1°. The vapor density was found 

 to vary from 25*59 at the lower temperature, corresponding to a 

 molecular mass of 51*18, to 10*29 at the upper temperature, cor- 

 responding to a molecular mass of 20*58. The results of the 14 

 experiments are given in a table, from which values a curve has 

 been plotted, showing the law of the vapor density variation. 

 From this it appears at once that the process of dissociation is a 

 perfectly continuous one, and that if such a molecule as H 2 F 2 

 exists, it must be formed only during a transition process and be 

 capable of persisting only in the presence of definite proportions 

 of molecules both more and less complex than itself. At about 

 32° the density apparently corresponds with H 2 F 2 , but the curve 

 gives no indication of statical equilibrium in the neighborhood of 

 this temperature such as would be manifest were such a molecule 

 capable of an independent existence. " At temperatures below 

 this point, the vapor-density gradually increases in a regular 

 manner until at 26*4°, the lowest temperature observed, the vapor- 

 density becomes 1*773 (airz=l) equivalent to a molecular mass of 

 51*2 (H 8 F 3 =:60) ; as it is heated the vapor behaves like a mix- 

 ture of a complex molecule H X F X or of H X F X and H y F y molecules 

 with a gradually increasing number of molecules of HF, the pro- 

 cess of dissociation being perfectly continuous until the tem- 

 perature increases to about 60° when the density becomes ap- 

 proximately normal ; that is, corresponds to a vapor consisting 

 wholly of HF molecules."— J. Chem. Soa, lv. 163, April, 1889. 



G. F. B. 



2. On the decomposition of Potassium chlorate by heat, in 

 presence of Manganese dioxide. — McLeod has studied the nature 

 of the reaction which takes place in the ordinary method of pre- 

 paring oxygen by heating a mixture of potassium chlorate and 

 manganese dioxide. He concludes that the mechanism of the action 

 of the manganese oxide on the chlorate is probably as follows: 

 First, the formation of permanganate, chlorine and oxygen 

 according to the reaction (KC10 3 ) 2 + (Mn0 2 ) 2 =K 2 Mn 2 8 + Cl 2 + 

 2 ; since chlorine is certainly evolved at the commencement of 

 the action. Second, the permanganate is decomposed by the 

 heat, producing manganate, an oxide of manganese and oxygen ; 

 a reaction which may be written in the ordinary way K 2 Mn 2 8 = 

 K 2 Mn0 4 + Mn0 2 + 2 . The third stage is not quite so clear. It is 

 very improbable, the author says, that the manganate is trans- 

 formed into permanganate by the oxygen from the chlorate, for 

 in certain of the experiments in which permanganate and chlo- 

 rate were heated together, manganate remained in the residue. 

 He regards it as more likely that the manganate is acted on by 

 more chlorine produced by the action of the peroxide on fresh 



