Mr. Tennant discovered in 1791 that carbonic acid combined with the earths and alkalies is capable of decomposition by phosphorus, in a red heat; and Dr. Pearson, following up the discovery, found that pure or caustic lime may be united to phosphorus by heat so as to form phosphuret of lime; and that this dry compound when put into water is decomposed and gives out bubbles of phosphuretted hydrogen gas, which as usual explode spontaneously on reaching the surface of the water and coming into contact with the air.
In 1810 I published the method of analysing phosphuretted hydrogen by Volta’s eudiometer; having found that this gas and oxygen may be mixed together in a narrow tube without explosion and afterwards exploded as other similar mixtures by an electric spark.
Dr. Thomson published an essay on phosphuretted hydrogen in the Annals of Philosophy for August, 1816. He agrees with me very nearly as to the constitution and properties of this gas, as far as I have gone; but he has ascertained several additional properties of the gas, which I shall advert to in the sequel.
Sir H. Davy and Gay Lussac have investigated several compounds of phosphorus, particularly with muriatic and oxymuriatic acids, and with the new metals potassium and sodium, which I shall have to notice in their proper places.
Other authors have written on phosphurets besides those I have mentioned, but they do not require to be particularly distinguished in this enumeration. We shall therefore proceed to describe the phosphurets more particularly.
1. Phosphuret of hydrogen.
From recent experiments which I have made on phosphuretted hydrogen gas, I find the account already given (Vol. 1. page 456) is deficient, and in several respects inaccurate; I shall therefore substitute the following, as more perfect and correct.
Phosphuretted hydrogen may be obtained nearly pure, by the methods recommended by Dr. Thomson. Phosphuret of lime that has been carefully secluded from the atmosphere, may be put into a small phial filled with water, acidulated by muriatic acid; into this a cork with a bent tube must be immediately put under water, so that the phial and tube are both full of water; gas soon begins to appear, which rising to the top of the phial, expels a corresponding portion of water, and in due time the gas itself comes over and may be received as usual: if the phial in which the gas is generated be warmed to 140 or 150°, the gas is given out more readily. A half ounce phial with 20 grains of phosphuret in small lumps, will produce 3 or 4 cubic inches of gas. If the phosphuret of lime has been previously exposed for a few hours to the atmosphere, the gas is more abundant, but consists chiefly of hydrogen, mixed with a little phosphuretted hydrogen.
Pure phosphuretted hydrogen is distinguished by the following properties: 1. It explodes when coming into the atmosphere in bubbles, and a white ring of smoke subsequently ascends: 2. It is unfit for respiration, and for supporting combustion: 3. Its specific gravity is 1.1 nearly, that of atmospheric air being unity: 4. Water absorbs fully ⅛ of its bulk of this gas, which is expelled again by ebullition or by agitation with other gases, but not without some loss: 5. A small portion being electrified for some time, deposits abundance of phosphorus, and expands from one volume to 1⅓ nearly, which is found to be pure hydrogen: 6. Liquid oxymuriate of lime absorbs phosphuretted hydrogen, converting it into phosphoric acid and water, and leaves any free hydrogen that may be present; hence we are enabled to ascertain the proportion of free hydrogen in any such mixture, an important point as far as regards this gas: 7. One volume of pure phosphuretted hydrogen, requires two volumes of oxygen for its complete combustion by an electric spark, in Volta’s eudiometer; (the gases must be previously mixed in a tube not more than ³/₁₀ of an inch in diameter, to prevent an explosion in the act of mixing, after which they may safely be transferred into any other vessel); the result of the combustion is phosphoric acid and water: 8. One volume of phosphuretted hydrogen, mixed with from 2 to 6 volumes of nitrous gas, may be exploded by electricity in Volta’s eudiometer; or it may be exploded by sending up a bubble of oxygen, without electricity; in like manner, may the mixtures of phosphuretted hydrogen and oxygen be exploded by a bubble of nitrous gas: 9. One volume of phosphuretted hydrogen, mixed with 4, less or more, of nitrous oxide, is also explosive by electricity, but the mixture undergoes no change without electricity, at least in a day: 10. Mixtures of phosphuretted hydrogen and nitrous gas have a slow chemical action, by which in from 1 to 12 hours, the phosphuretted hydrogen is burnt and the nitrous gas decomposed into nitrous oxide and azotic gas: 11. According to Sir H. Davy and Dr. Thomson, phosphuretted hydrogen gas being heated along with sulphur in a dry tube, the gas is decomposed and a new gas, sulphuretted hydrogen, is formed, and the phosphorus unites with the sulphur. Davy says the gas is doubled in volume by this operation; but Thomson says it remains the same; some doubt therefore exists respecting this fact: 12. When phosphuretted hydrogen gas is let up to oxymuriatic acid gas, a quick combustion with a yellow flame is observed, and the result varies according to the proportions: when one volume phosphuretted hydrogen is put to 3 or 4 of acid gas, both of the gases disappear, and muriatic and phosphoric acids are produced.
As these properties differ in many respects from those hitherto assigned to this gas, it will be necessary to enlarge upon them. The sp. gr. of this gas has already been adverted to, (Vol. 1.), and its great variation from .3 to .85; more recently Dr. Thomson finds it about .9. In all these instances it was, I have no doubt, contaminated with less or more of hydrogen; at least it was so in my own instance; for, I have the proportion of oxygen which it required for its complete combustion, both before and after it was weighed. It was what I then thought pure gas: that is, 100 volumes required nearly 150 of oxygen; but I am now convinced that gas of this description contains ⅓ of its volume of free hydrogen; hence the correction of the sp. gravity. Davy estimates the sp. gr. of the gas which he denominates hydrophosphoric at .87 or 12 times that of hydrogen; this gas, as will appear from this and other properties, is in all probability phosphuretted hydrogen gas, nearly pure.