shall be in a position to discuss the organic relations of both these substances under one head.

The substance phosphorus-of which I here show you a specimen in its common or ordinary condition— although presenting many analogies with sulphur, differs from that substance in many important respects. Sulphur is yellow; phosphorus, when pure, almost colourless sulphur is very brittle; phosphorus only brittle to an inconsiderable extent: sulphur is combustible, but does not undergo change when exposed to the air; whereas phosphorus, when similarly circumstanced, unites continuously with oxygen, producing intermediately that peculiar exalted or ozonised condition of oxygen, which I have already treated of in a former lecture. ·

As regards the conditions under which sulphur and phosphorus occur in nature, there is the great difference between the two,-that whereas sulphur is only found in small proportions diffused throughout organic nature, so that whenever we desire to procure it the mineral kingdom is our great magazine,--phosphorus, on the other hand, is but sparingly diffused as a component of minerals: it is to the animal kingdom that we turn for our supplies of phosphorus-to bones and the fluids of the body. These are our magazines of phosphorus, from which, by processes well understood, the substance is extracted in the large quantities. now required for lucifer matches and the other manufactures into which phosphorus enters.

The leading characteristic of phosphorus is its extreme combustibility, of which you have already seen an example on the occasion of my treating of oxygen. To illustrate this property in a familiar way, let me just take a minute portion of phosphorus upon the tip of a brimstone match, and rub it—immediately you will observe the match take fire; but the phenomena and the effects of the combustion of phosphorus will be well illustrated by igniting a small portion in an open tube,—which I proceed to do.

Having placed a small fragment of phosphorus in this open tube, I apply heat and ignite it,—when, on impelling a current of air through the tube the phosphorous burns with great rapidity. The combustion having terminated, you will observe the appearance of two different residues-one being a red-coloured substance, and the other white. The latter, or white, substance, is an acid compound of phosphorus with oxygen. Just this sort of result we should, a priori, have expected; the former was long imagined to be a combination of phosphorus with oxygen also, but in a lesser ratio than necessary to constitute an acid. Within the last few years, however, M. Schrötter, of Vienna, demonstrated that the red compound in question was merely phosphorus. No combination has taken place to form this red compound, but the phosphorus has assumed a second, or allotropic condition, just as sulphur under the operation of heat does the

same.

This allotropic or amorphous phosphorus, prepared in this small quantity by our tube apparatus, is now made on the large scale, and commercially applied to numerous purposes for which common phosphorus was formerly used; and with advantages which will presently appear.

Before we can have a just appreciation of the value of allotropic phosphorus, we must study the characteristics of this substance by comparison with phosphorus in its ordinary condition. Common phosphorus is remarkably combustible; tending to burst into flame on the application of very slight friction or low degree of heat; a quality which renders it well adapted to the purpose of forming lucifer matches. The quality of its colour, and its physical condition as to softness,

Well, here is a lump you will observe the

are also points of comparison. of allotropic phosphorus, and difference between the two. In the first place, the colour is totally different, that of the allotropic variety being dark; then the fracture is different, that of allotropic phosphorus being harshly brittle;-but the most striking difference between the two varieties of phosphorus is brought out by the application of friction, or of heat. Common phosphorus we are obliged to keep in water, for the purpose of guarding against spontaneous combustion; allotropic phosphorus, however, may be kept unchanged in atmospheric air; indeed, it may be wrapped. up in paper, and carried in the pocket even, with the most perfect impunity and in this way Professor

Schrötter quite surprised us by his temerity, until we at length gained confidence, and became acquainted with the real qualities of the new substance. Common phosphorus when rubbed takes fire; the allotropic variety, however, may be rubbed with impunity up to a certain point, after which its combustive qualities are brought out. But the extreme use of allotropic phosphorus in the arts will not be comprehended until you are informed of the frightful ravages produced by the vapours of common phosphorus on those who are subjected to their influence, as is the case in manufactories of lucifer matches. Persons thus situated are afflicted with a disease which corrodes, ulcerates, and destroys their bones, causing the most horrible torture, and frequently death. The employment of allotropic phosphorus is attended with no such calamitous results; and being capable of changing into ordinary phosphorus on the application of an adequate amount of heat or friction, it answers perfectly well for lucifer matches, and indeed most of the ordinary applications of phosphorus.

In many other respects these two conditions of phosphorus present differences. Thus, for instance, the power of solution in menstrua is different. Common phosphorus readily dissolves in the sulphuret of carbon, whereas allotropic phosphorus does not. Of this I can show you a ready proof, by pouring two portions of sulphuret of carbon respectively on common and on allotropic phosphorus. You can observe that there is a

but we

manifest difference as to the amount of solution; shall have a better proof by and by. Pouring a little of each of these solutions on two pieces of paper respectively the sulphuret of carbon, being exceedingly volatile, evaporates; when, observe-one piece of paper takes fire, owing to the amount of of dry phosphorus deposited upon it, whilst the other remains. unburnt.

This allotropic change of state is one of the most curious developments of modern chemistry; and now that our attention is directed to the subject, numerous manifestations of this condition are recognisable. Not the least curious fact in connection with this matter is that heat is not an invariable, an indispensable condition to developing the allotropic condition. Thus, for instance, if I add a solution of bichloride of mercury to a solution of iodide of potassium, I may get a yellow or a red compound, yet the composition of both is identical. Heat effects a similar change. On this paper is painted a red cross- -the red iodide of mercury being used as a pigment. If I hold the paper on which is this red cross over a spirit lamp flame, the redness presently changes to yellow. But I must not linger over this interesting subject of allotropism-my time admonishes me to bring before your notice the curious fact of the existence of sulphur and phosphorus in the organic world-phosphorus in large quantities, as I have already indicated; but sulphur in amounts more small-nevertheless, its presence in animals is universal.