There was absolutely nothing to attract public attention in the purchase from time to time of common, well-known substances, such as sulphur, quicklime, naphtha, &c. &c., by the authorities of the Arsenal; but the suspicions of the spies and traitors, always to be found in Constantinople,[68] would have been instantly roused by the importation of any new or rare substance such as saltpetre. And whence could saltpetre have come? M. Berthelot recognises the importance of this question, although he cannot answer it: “Comment se procurait-on le salpêtre?... Aucun renseignment n’est venu nous l’apprendre. Ce point pourtant est capital.”[69] Saltpetre would naturally have been obtained from the countries where it was most abundant and cheapest—from the East; but the Greeks could not have relied upon this source of supply, for whenever political complications arose between the Emperor and the Caliph—and they were interminable—the ports of Egypt and Syria were closed against Greek ships. However, saltpetre did not grow in the streets of Constantinople: the natural salt (if used) must have been collected somewhere, and sold to Government by someone, and transported somehow to the capital; and what despot could have tied the tongues of collectors, merchants, sailors, and porters? The mere facts that only one State trafficked in saltpetre, that this State only bought it in time of war, and that this State alone employed sea-fire, would have immediately betrayed the secret of its composition to these men, and what was known to them was known to the world. It is most improbable that the use of saltpetre could have been concealed for one year, much less the five hundred years during which the secret of the sea-fire was successfully guarded. I may be reminded of the Emperor Constantine VII.’s statement (in Chap. xiii. of his “Administration, &c.”), that on one occasion a Roman general, corrupted by a large bribe, did reveal the secret and shortly afterwards, when entering a church, was consumed by fire which fell from heaven upon him. The story is obviously legendary. The venal general is as unreal as the fire from heaven; he is merely introduced to us as “an awful example,” and we cannot endow him with reality by rejecting the fire. The claim of the Marquess Carabbas to reality is not established by denying the existence of Puss-in-Boots. Had the secret been divulged the sea-fire would have been used against the Greeks, and no mixture that can be identified with it ever was.
A saltpetre mixture, then, would not, in all probability, have fulfilled the first condition, nor would it have fulfilled the second. There is no conceivable connection between saltpetre and the sea, or water in general. A saltpetre mixture (of suitable proportions) would have proved a much better incendiary than Greek fire, but it would have acted as effectively from a fort as from a ship. Indeed, if we consider the ill effect of the moist sea air on the impure saltpetre of early times, we are justified in saying that the action of such mixtures on land would have been better, in general, than at sea.
A saltpetre mixture would have fulfilled the third condition by burning with much noise and smoke, which we may suppose to be the essential meaning of the Emperor Leo’s phrase, “thunder and smoke.”[70] We cannot reasonably attach greater significance to one of the commonest of all metaphors, thunder, which has been applied times unnumbered to the human voice, to the bursting of a child’s cracker,[71] and to the whirring of a dart. “Never burst such peals from the thunder-cloud,” says Vergil, as were produced by the javelin thrown by Æneas.[72]
As regards the fourth condition, the above statement of the Emperor Constantine about sea-fire and siphons[73] completely justifies us in concluding that there was some necessary connection between the two things. Now, there was no necessary connection between saltpetre mixtures, even when explosive, and siphons. Small quantities of such mixtures could have been, and eventually were, thrown by hand, in grenades, like Greek fire. Saltpetre mixtures, therefore, would not have fulfilled the fourth condition.
The result of the foregoing inquiry is, that a saltpetre mixture would have only fulfilled one, the third, of the four conditions to which the sea-fire was subject; and we have now to cast about for some mixture of known substances, not hitherto combined together for warlike purposes, which would have fulfilled them all.
A clue to the composition of the Kallinikos mixture may perhaps be found in its Greek name, “sea-fire” or “wet-fire.” One substance had long been known with whose combustion water was closely connected—quicklime, and with its properties Kallinikos, as an architect, must have been perfectly familiar. Its temperature rises—to 150° C. (302° F.) if the quantity be large—when sprinkled with water, and it can consequently be employed to ignite substances with low points of ignition. For example, if a mixture of quicklime and naphtha be thrown into water, the rapid rise in temperature of the lime causes a sudden and strong development of vapour from the naphtha, which on mixing with the air becomes highly explosive. Such a mixture, it is almost unnecessary to add, could not be handled with safety after it has been wet. Plutarch was aware of the explosive nature of naphtha vapour. “Naphtha,” he says, “is like bitumen, and is so easy to set on fire that, without touching it with any flame, it will catch light from the rays which are sent forth from a fire, burning the air which is between both.”[74] Pliny speaks of the heat developed by quicklime when sprinkled with water. “It is strange,” he says, “that what has already been burnt should be ignited by water” (mirum aliquid, postquam arserit, accendi aquis).[75] The same property is implicitly referred to in the “Kestoi,” attributed to Sextus Julius Africanus of Emaus, who lived under Alexander Severus, 222-235. The military portions of this work, however, must have been written long afterwards, in the end of the sixth or the beginning of the seventh century at the earliest; for Belisarius, who was born in 505, is mentioned in the sixty-sixth chapter.[76] In the forty-fifth chapter there is a recipe for a quicklime-asphalt composition, which is called “automatic fire.” This mixture was used by jugglers to exhibit “spontaneous combustion,” a little water being secretly poured on a plate on which a ball of the composition was placed.[77] It contained very little quicklime (παντελῶς ὀλίγον). Cameniata tells us that at the storming of Salonika in 904 the Moslems threw “pitch and torches and quicklime” over the walls.[78] By “quicklime” he probably meant the earthenware hand grenades, filled with wet quicklime, described by the Emperor Leo, who then sat on the throne (886-911). “The vapour of the quicklime,” he says, “when the pots are broken, stifles and chokes the enemy and distracts his soldiers.”[79]
The simplest and most probable explanation of the nature of the sea-fire then is, that it was a sulphur-quicklime-naphtha mixture of the same family as those shown in the following Table.
TABLE III.
Sea-Fires.