Gun-cotton, upon the relation between the quantity as well as the degree of heat applied and the amount of surface of the Gun-cotton, and upon other conditions. While a small spark, or a thin platinum wire heated to full redness, only induces slow combustion in the compact Guncotton yarn, a thick rod of iron, heated only to dull redness, will invariably inflame it in the ordinary manner. A piece of open yarn cannot be ignited so as to burn in the slow manner; on the other hand, the more compactly the Gun-cotton is twisted, the more superficial is the slow form of combustion induced in it; indeed, the Gun-cotton may be rendered so compact that it will simply smoulder in open air, if ignited as described, leaving a considerable carbonaceous residue; and the heat resulting from this most imperfect combustion will sometimes be abstracted by the escaping gases more rapidly than it is developed, so that the Gun-cotton will then actually cease to burn, even in open air, after a short time.

The remarkable facility with which the effect of heat upon Guncotton may be modified, so as even to produce results totally opposite in their characters, as exemplified by some of the experiments which have been described, renders it easily conceivable that this material may be made to produce the most varied mechanical effects, when applied to practical purposes; that it may indeed be so applied as, on the one hand, to develope a force, very gradual in its action, which may be directed and controlled at least as readily as that obtained by the explosion of gunpowder, while, on the other hand, it may be made to exert a violence of action and a destructive effect far surpassing those of which gunpowder is susceptible. The results arrived at in Austria, which show that Gun-cotton may be made to produce effects from three to eight times greater than those of gunpowder, cease to be surprising after a study of the chemical and physical characteristics of this interesting explosive agent.

The products obtained by the explosion of Gun-cotton, and its decomposition under various conditions, have as yet been very imperfectly studied, but there is little doubt that they vary in their nature almost as greatly as the phenomena which attend the exposure of the material to heat under different circumstances. It is well known that, when Gun-cotton is inflamed in the open air, there is produced (in addition to water, carbonic oxide, carbonic acid, and nitrogen) a considerable proportion of binoxide of nitrogen, so that the gaseous mixture assumes a red-brown tinge, and becomes very acid when it mixes with air. The products of the different forms of imperfect combustion which Gun-cotton has been described as susceptible of undergoing, are undoubtedly much more complex in their character than those just referred to. They include at times a proportion of some substances, not yet examined, which make their appearance as a white vapour or smoke; cyanogen can readily be detected in all the products of imperfect combustion; the proportion of binoxide of nitrogen is generally so large that the gaseous product becomes very highly coloured when mixed with air; peroxide of nitrogen has also

been observed in some instances; lastly, there is little doubt that the products occasionally include a proportion of oxidizing gases.

The products which have just been alluded to are the results of the decomposition of Gun-cotton either at ordinary or diminished atmospheric pressures; when the explosion of the material is effected in a confined space, in such a manner that the main decomposition takes place under pressure, the metamorphosis which the material undergoes is of a more simple and complete character.

It has been found by Karolyi that, when Gun-cotton is exploded by voltaic agency in a shell which is burst by the explosion, and which is enclosed within an exhausted chamber, so that the products of decomposition are collected without danger, the results obtained under these conditions are comparatively simple; the analysis of the contents of the chamber, after the explosion, showed that they consisted of carbonic acid 20.82 per cent., carbonic oxide 28 95, nitrogen 12.67, hydrogen 3.16, marsh gas 7.24, water 25 34, and carbon I 82. The decomposition of Gun-cotton under these conditions (which are similar to those of its explosion when employed as a destructive agent) appears, therefore, not to be attended by the production of any oxide of nitrogen. The lecturer found, in some preliminary experiments made under the same conditions as those of Karolyi, that only a minute proportion of binoxide of nitrogen was produced. These results, when compared with those obtained by the ignition of Gun-cotton in open air and rarefied atmospheres, show that, just as the decomposition of this material is of a more complicated and intermediate character, in proportion as its combustion is rendered imperfect by diminution of pressure or other circumstances, so, conversely, the change which it undergoes will be the more simple, and its conversion into gaseous products the more complete, the greater the pressure, beyond normal limits, under which it is exploded: that is to say, the greater the resistance offered to the generated gases upon the first ignition of a charge of Gun-cotton (and consequently the higher the temperature at which the decomposition of the confined Gun-cotton is effected). It is therefore readily intelligible that the notions hitherto generally entertained with regard to the very noxious character of the products of explosion of Gun-cotton and their powerfully corrosive action upon metals-based as these notions have been upon the effects observed on exploding Gun-cotton in open airhave been proved to be erroneous by the results of actual application of Gun-cotton to artillery and other purposes. The foregoing considerations contribute, moreover, to the ready explanation of the fact, established by the experiments in Austria, that the destructive effect of Gun-cotton is greatly increased, within certain limits, by increasing the resistance which the products of explosion have to overcome before they can escape into the air.

The conditions (of temperature, pressure, &c.) which influence the nature of the decomposition of Gun-cotton, exert, unquestionably, a similar influence upon the nature of the explosion of gunpowder, and upon the mechanical effects which the products are capable of exerting,

Observations made by the lecturer, in experiments upon the ignition of gunpowder in rarefied atmospheres, point to the existence of products of comparatively complicated character among those found by the gradual decomposition of that material under the conditions described. The earlier investigations (Gay-Lussac, Chevreul, &c.), of the products of explosion of gunpowder, represent these as being of a very simple character, and in harmony with the theory that gunpowder is converted essentially by its explosion into carbonic acid (or a mixture of that gas and carbonic oxide), nitrogen and sulphide of potassium. But, more recent experimenters, Bunsen and Schischkoff, who have made a very elaborate examination of the products which they obtained by the explosion of gunpowder, represent the change to be one of a very complicated character; fix the percentage of solid substances found at a much higher figure than that hitherto accepted, and show that the sulphide of potassium, which has been considered as the principal of these products, was only produced in very small proportion, in their experiments. The conditions under which these chemists exploded the gunpowder did not, however, correspond at all in their character to those under which gunpowder is exploded in actual practice, and would, therefore, be very likely to furnish results greatly at variance with those produced when a charge of powder is fired in a gun, a shell, or a mine. That sulphide of potassium is abundantly produced, upon the discharge of a fire-arm, appears beyond doubt; it may be readily detected in the solid matter which remains in the barrel near the breech; it may be found deposited in considerable quantity near the muzzle of the arm, and there appears strong reason for believing that the flash of flame, observed at the mouth of a fire-arm upon its discharge, is due in part to the ignition, as it comes into contact with the air, of sulphide of potassium, which has been vapourized by the heat of the explosion, and is thus mixed with the escaping gases.

In comparing the effects of Gun-cotton, as an explosive agent, with those of gunpowder, and in basing theories, with regard to the difference in the mechanical effects exerted by the two, upon the analytical results of the products of their explosion which have been obtained up to the present time, it is necessary to proceed with great caution; for exceptional results cannot form any sound basis for correct theories or tenable arguments. It can only lead to incorrect conclusions, which may considerably retard the thorough investigation of a most important subject, if the facts be ignored or lost sight of, that, firstly, the condi tions which practically influence the nature of the products of the explosion of Gun-cotton have a similar influence upon the change which gunpowder may be made to undergo; and that, secondly, the effect of heat upon the water produced by decomposition of Gun-cot ton, which forms so important an element in the action of this explosive, has most probably its parallel, to no unimportant extent, in the vapourizing effect of heat upon the solids (especially upon sulphide of potassium) produced in the explosion of gunpowder. These are matters which demand their full share of consideration and investigation, before

it can be admitted that a sufficient explanation of the remarkable differences between the effects of gunpowder and Gun-cotton exists in the assumption, that certain products of decomposition of the former must be regarded entirely as waste matter in the material, simply because they are solid at ordinary temperatures. The fact, that Guncotton is entirely converted into gases and vapour at the moment of explosion, constitutes unquestionably one of the great advantages which that substance possesses over gunpowder; but it is premature, at present, to assume, in comparing the action of the two substances, that only thirty-two (or even sixty) per cent. of gunpowder exist as gas or vapour, at the moment of its explosion.

It is to be expected that the investigations which are now being actively pursued upon the true chemical effects produced in the explosion both of Gun-cotton and Gunpowder, under conditions similar to those which attend their employment in practice, will aid materially in furnishing the correct data so essential for a thorough and impartial comparison of the nature and merits of these two explosive agents.

[F. A. A.]

WEEKLY EVENING MEETING,

Friday, April 22, 1864.

COLONEL SIR GEORGE EVEREST, C.B. F.R.S. in the Chair. PROFESSOR JOHN S. BLACKIE, M.A.

OF THE UNIVERSITY OF EDINBURGH.

On the Spartan Constitution and the Agrarian Laws of Lycurgus.

THE peculiar institutions and laws which go under the name of Lycurgus-in some respects a wonder and a problem to the ancients themselves-have in recent times received a very full and detailed discussion from some of the most distinguished scholars of Germany and England. Foremost among these, of course, is to be mentioned Ottfried Müller, in his great work on the Dorians; then, particularly, the historico-archæological disquisitions of C. F. Hermann and Schoemann; with the admirable summing-up the results of these investigations in the historical works of Curtius and Duncker. In our own country, after the solid and substantial substructure of Thirlwall, ground was broken by Dr. Arnold in one of the notes to his Thucydides, and the views there set forth were carefully sifted, and the whole question stated with complete originality and independence by the late Sir George C. Lewis in an essay in the Cambridge Philological Museum. After this, Mr. Grote, in the second volume of his great

historical work, propounded his views on the Spartan institutions generally, with great originality and boldness, and specially on the famous Agrarian laws. After such labours of such men, it seems not unreasonable to think that we should have now arrived at some certain and indisputable conclusions, on which those who read Aristotle, Isocrates, and Xenophon some two hundred years ago, could only have very misty apprehensions. It is the intention of this discourse, accordingly, shortly to review the results which, in this most interesting field of archæological research, we seem to have arrived at ; and in doing so the method which I shall adopt is to state shortly, in the first place, the undisputed points in reference to the Spartan Constitution-that is, such points as all well-instructed scholars, being men of sound judgment, and not hunters after novelty, are now agreed on; and in the second place, to discuss in detail one of the most characteristic of the Spartan institutions, which is still lying under the severe ordeal of Mr. Grote's sceptical reprobation, and which, therefore, cannot be considered as undisputed among European scholars.

Among the undisputed points I notice the following:

1. The political constitution of Sparta was a broad aristocracy, limited to some extent by regal rights and usages, but in no degree modified by popular influence in the modern, or even in the Roman or Athenian, sense of that term. By a broad aristocracy, I mean a large corporation of privileged proprietors, varying from 10,000 to 2,000, with a monopoly of political power, exercised indeed by different individuals in different degrees, but altogether exclusive of the great mass of the population, who were politically null, as much, or rather a great deal more than the unenfranchised class in this country, because they were in no sense recognized as members of the body politic, were never appealed to even in the most distant way, and had no influence of any kind in public affairs. This broad aristocracy was, in fact, the whole Spartan people, who, as Dr. Arnold properly expressed it, were "a nation of nobles," a brotherhood of privileged warriors, permanently encamped in a country whose native population they treated as a nullity, as much as the laity is ignored by the clergy of the Romish Church. The only limitation to which the great power of this aristocracy was subject, is found in the influence of the kings; and this, connected as it was with the great element of religion, and the important functions of war, must, when assisted by the weight of personal character, have often been considerable. Nevertheless, monarchy in Lacedæmon, weakened as it was by the general strength and breadth of the aristocracy, and also by the early splitting of the undivided Homeric kingship into two-itself the strongest proof of the great strength of the old aristocracy--never could have been in a position to stamp a permanently distinctive character on the constitution. Its proper type always was aristocracy: a "close, unscrupulous, and well-obeyed oligarchy" according to Mr. Grote, if any person prefers that phraseology.

2. The Spartan privileged class—that is, the whole Spartan people,