It may be proper to advert more particularly to the hydrophosphoric gas of Davy. That this gas is the same as that we have been describing, can hardly admit of a doubt. Their near agreement in sp. gr., in their absorbability by water, in the quantity of oxygen requisite for their combustion, in their moderate expansion by burning with a minimum of oxygen and in their combustibility by oxymuriatic acid, are circumstances sufficient to warrant their identity. It is said that by heating potassium in this gas, one volume yields two of hydrogen; but it has not been found to yield two volumes by electricity, the more accurate criterion. Besides, both Davy and Gay Lussac find that potassium heated in the more common phosphuretted hydrogen expands it from 1 to 1⅓ or 1½ volume, which common electricity will not do; it is presumed therefore that the potassium in some way conduces to the production of a portion of the hydrogen. Spontaneous ignition or explosion is, I believe, no distinctive mark of variety in phosphuretted hydrogen; when this gas is _produced_, it is usually explosive from the uncombined phosphorus which it elevates; but the best and purest phosphuretted hydrogen loses the property wholly or partially by standing a while over water, though it loses no sensible part of its phosphorus. It is commonly stated that phosphuretted hydrogen deposits phosphorus by long standing. This seems to be true; but the deposition is slower than I imagined. Seven years ago I set aside a bottle of impure phosphuretted hydrogen which I then labeled, 10 combustible take 14.6 oxygen; this bottle has not been preserved with special care to seclude the atmosphere; notwithstanding that, it is now such, that 10 combustible take 6.7 oxygen, and hence it still contains some genuine phosphuretted hydrogen. 2 _and_ 3. _Phosphurets of carbone and sulphur._ See VOL. 1. page 464. _4. Phosphuret of lime._ This compound may be formed by subliming phosphorus in a glass tube containing small fragments of recently calcined lime, heated to a low red. The sublimed phosphorus coming into contact with the hot lime, the two unite with a vivid glow, and in due time mutual saturation is produced. The result is a dry, hard compound of a deep brown or reddish colour, which on cooling must be put into a bottle and well corked, if not intended for immediate use, as it soon changes by the action of atmospheric air and moisture. With this precaution, I have reason to think it may be kept unimpaired for years. As far as I know, no experiments have been published relating to the proportion in which phosphorus and lime unite. M. Dulong, in a valuable paper on the combinations of phosphorus and oxygen, in the _Memoires de la Société d’Arcueil_, VOL. 3. (1817,) has given some account of his experiments on the earthy phosphurets; but it is to be regretted that he has given none on the proportions of their elements.