tions, the receiver being changed with each rise of 10° in the retort, and the liquid retained in a state of incipient ebullition. In this way a succession of products were obtained, but they were by no means constant; for the portions, for instance, which came over when the fluid was boiling from 160° to 170°, when re-distilled began to boil at 130°, and a part remained which did not rise under 200°. By repeatedly rectifying all these portions, and adding similar products together, I was able to diminish these differences of temperature, and at last bring them more nearly to resemble a series of substances of different volatility. During these operations I had occasion to remark, that the boiling-point was more constant at or between 170° and 190°, than at any other temperature, large quantities of fluid distilling over without any change in the degree, whilst in other parts of the series it was constantly rising. This induced me to search in the products obtained between these points for some definite substance; and I ultimately succeeded in separating a new compound of carbon and hydrogen, which I may by anticipation distinguish as bicarburet of hydrogen.
Bicarburet of Hydrogen.—This substance was obtained in the first instance in the following manner:-Tubes containing portions of the above rectified products were introduced into a freezing mixture at 0°; many of them became turbid, probably from the presence of water; one received at 170° (by which is meant that that was the boiling-point of the contents of the retort when it came over) became partly solid, crystals forming round the side, and a fluid remaining in the centre; whilst two other portions, one received at 180° and the other at 190°, became quite hard. A cold glass rod being introduced into one of these tubes, the mass within was found to resist considerable pressure; but by breaking it down, a solid part was thrust to the bottom of the tube, whilst a fluid remained above: the fluid was poured off, and in this way the solid portion partly purified. The contents of the tube were then allowed to fuse, were introduced into a larger and stronger tube, furnished with another which entered loosely within it, both being closed of course at the lower end; then again lowering the temperature of the whole to 0°, bibulous paper was introduced, and pressed on to the surface of the solid substance in the large tube by the end of the smaller one. In this way much fluid
