Page:Experimental researches in chemistry and.djvu/236

1827.] ultimately there remained nothing in several of the receivers but a brown substance, heavy, adhesive like honey or treacle, and in certain cases even almost solid. From the circumstances of the experiments, no hesitation could arise in concluding that a spontaneous chemical change had taken place; and it does not seem at all unlikely that a similar change, or one to a much greater extent, may have occurred suddenly during the rapid alteration in the mechanical condition of the gas in Mr. Gordon's experiment; the most con dens able of the substances in the mixture of' elastic matters which constitute oil-gas, being perhaps those which are most altered, and in that case Mr. Gordon's account of the phenomena would be correct.

Transference of Heat by change of Capacity in Gas.

of the copper vessels in which gas is compressed at the Portable-Gas Works are cylinders from two to three feet in length, terminated by hemispherical ends. These are attached at one end to the system of pipes by which the gas is thrown in, and being so fixed, the communication is opened; it frequently happens, that gas previously at the pressure of thirty atmospheres in the pipes and attached recipients, is suddenly allowed to enter these long gas-vessels, at which time a curious effect is observed. That end of the cylinder at which the gas enters becomes very much cooled, whilst, on the contrary, the other end acquires a considerable rise of temperature. This effect is produced by change of capacity in the gas; for, as it enters the vessel from the parts in which it was previously confined, at a pressure of thirty atmospheres it suddenly expands, has its capacity for heat increased, falls in temperature, and consequently cools that part of the vessel with which it first comes in contact; but the part which has thus taken heat from the vessel being thrust forward to the further extremity of the cylinder by the successive portions which enter is there compressed by them, has its capacity diminished, and now gives out that heat, or a part of it, which it had the moment before absorbed; this it communicates to the metal of that part of the gas-vessel in which it is so compressed, and raises