1865.] :Phjsics. . 695 



temperature at which it took place was only raised one or two degrees. 

 He concludes that the difficulty gases have in quitting liquids holding 

 them in solution comes of a purely physical adhesion, and not of a 

 chemical a ffini ty. 



A paper by M. Fizeau, on the Dilatation of the Diamond, and 

 Crystallized Protoxide of Copper under the influence of heat, pre- 

 sented to the Academy of Sciences at their sitting in June last, 

 contains some curious observations. 



The author finds that these bodies, like water, present a maximum 

 of density at a certain temperature. The diamond, for example, has 

 its maximum at - 38 • 8° C, and protoxide of copper at 4°. M. Fizeau 

 has also determined the co-efficients of dilatation in these two bodies. 

 These are the first two solid bodies in which the maximum of density 

 has been satisfactorily determined, although the probability of a 

 variation with temperature has been shown. 



The thermic equivalent of magnesium has been determined by 

 Dr. T. Woods,* by a method described by him in 1852, namely, by 

 dissolving the metal in dilute sulphuric acid, marking the rise of 

 temperature of the fluid and correcting the result by making the 

 proper allowances for the heat absorbed by the decomposition of the 

 water, and that evolved by the combination of the magnesia with the 

 acid. The result at which the author has arrived, is that the quantity 

 of heat developed by the combustion or oxidation of an equivalent of 

 magnesium is exactly twice as much as that produced by the oxidation 

 of an equivalent of zinc. Zinc will raise the temperature of 1,000 

 grains of water 9 ■ 6° Fahr. by the combustion of 4 grains or 1 

 equivalent, oxygen = 1. Magnesium by the combustion of 1^ grains, 

 or 1 equivalent, will raise the temperature of 1,000 grains of water 

 19 -2° Fahr. This is the greatest amount of heat produced by an 

 equivalent of any substance with which we are acquainted. 



A useful paper on the easily fusible alloys of cadmium has been 

 published by Dr. C. R. von Hauer. The alloys were made by fusing 

 the ingredients in a covered porcelain crucible at the lowest possible 

 temperature. After stirring with a glass rod, the fused mass was 

 poured upon a cold metal plate, where it instantly solidified. The 

 specific gravity and the melting point were determined after the alloy 

 had been so melted and cooled two or three times. In the two or 

 three fusions a partial oxidation of the metals takes place, which 

 occasions a slight alteration in the equivalent proportions, and which 

 it is almost impossible to avoid. The melting point was determined 

 under hot water, and also by placing a thermometer in the fused mass 

 without water. Under water the alloys quickly oxidize. They have 

 also the property of becoming pasty below their proper melting point, 

 which may lead to error in the determinations. The author's de- 

 terminations were made when the alloy was really fluid. 



The following table gives the equivalent proportions of the 



* • Phil. Mag.,' July, 18G5. 



