I am not prepared at present to state the exact reaction which takes
place between salts of calcium and magnesium and a compound soap
containing sodium oleate and stearate. I publish these results because
I have not noticed anywhere the fact that some waters show a greater
hardness with soap when their temperatures approach the boiling point
than they do at the average temperature of the air, it being, I
believe, the ordinary impression that cold water wastes more soap than
hot water before a good and useful lather can be obtained, whereas
with very many waters the case is quite the reverse. Neither am I
aware at present whether it is well known that the use of sodium
oleate unmixed with sodium stearate dispenses with the process of
dilution even in very hard waters.--_Chem. News._
* * * * *
THE DENSITY AND PRESSURE OF DETONATING GAS MIXTURES.
MM. Berthelot and Vielle have recently been studying the influence of
the density of detonating gaseous mixtures upon the pressure
developed. The measure of pressure developed by the same gaseous
system, taken under two initial states of different density to which
the same quantity of heat is communicated, is an important matter in
thermodynamics. If the pressures vary in the same ratio as the
densities, we may conclude, independently of all special hypotheses on
the laws of gases, first, that the specific heat of the system is
independent of its density (that is to say, of its initial pressure),
and depends only on the absolute temperature, whatever that may mean;
and secondly, that the relative variation of the pressure at constant
volume, produced by the introduction of a determinate quantity of
heat, is also independent of the pressure, and a function only of the
temperature.
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