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.
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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. Lastly, the pressure itself will vary proportionally with the absolute temperature, as defined by the theory of a perfect gas, and will serve to determine it. MM. Berthelot and Vielle operated with a bomb, at first kept at ordinary temperatures in the air, and afterward heated in an oil bath to 153 deg. Cent. They also employed isomeric mixtures of the gases; methylic ether, cyanogen, hydrogen, acetylene, and other gases were experimented upon, and the general conclusions are as follows: 1. The same quantity of heat being furnished to a gaseous system, the pressure of the system varies proportionally to the density of the system. 2. The specific heat of the gas is sensibly independent of the density as well toward very high temperatures as about deg. Cent. This is all true for densities near to those that the gas possesses cold under normal pressure, and which varied in the experiment to double the original value. 3. The pressure increases with the quantity of heat furnished to the same system. 4. The apparent specific heat increases parallel with this quantity of heat. These conclusions are independent of all hypotheses on the nature and laws of gases, and were simply drawn from the experiments in question.