Having in the preceding Section, entered somewhat largely on the nature and properties of Gunpowder, and consequently of the ingredients which compose it, any further observations on them would be unnecessary, providing the ingredients and proportions always remained the same. But as the ingredients used in the manufacture of that article are frequently employed in various other proportions, to form compositions for filling fire-works, it is necessary to give some further directions for the choice and purification of these articles, which, together with the apparatus made use of in the making of fire-works, will form the subject of the present section.
1.Nitre.—Among the various articles made use of in the composition, none are of greater importance than salt-petre, for on the quantity and purity of this depends all the force and much of the brilliancy of the fire. The most common sort is that usually sold by the grocers, and is generally in large lumpsformed of an assemblage of small crystals somewhat transparent, and often mixed with earthy matter and many other impurities. In its purest state it is in the form of small six-sided prismatic crystals, not apt to grow moist or powdery on exposure to the air. The pure nitre is now become very expensive, so it is of consequence to know how the common nitre, or nitre of commerce may be purified, for it is found to answer no purpose in Pyrotechny unless such change or purification in it have been effected.
Nitre is found, (like most of other saline bodies) to be much more soluble in boiling water, than in water of the ordinary temperature. If therefore the nitre of commerce be dissolved in a small quantity of boiling water, and the solution be properly strained, the liquor, when cold, will afford crystals that are very pure. The following is the most convenient method of proceeding: dissolve the nitre in boiling water, (which should be soft water,) in the proportion of about a quart to each pound of nitre; and that the solution may be more easily effected, let the nitre be reduced to a powder, previous to its being immersed, and let the vessel containing the nitre and water be kept at the boiling heat till all the salt is dissolved; then strain the liquor, while hot,through thick blotting paper, placed in a clean funnel; and set by the filtered liquor in a shallow vessel, in a cold place, to crystallize. The crystals thus obtained are to be dried, first in blotting-paper, and then before the fire, and kept for use. From the remaining solution, which is sometimes calledmother-water, fresh crystals may be procured by boiling it in a clean tin vessel till a filming scum arises to the surface, then filtering it through paper, and setting it aside to crystallize as before.
Very pure nitre may also be obtained from damaged gunpowder, which may be sometimes procured at a cheap rate, at the shops where it is sold for this purpose. The damaged powder must be ground with a small quantity of hot water, in a large wooden or stone mortar, otherwise it may be boiled over a gentle fire, with as much water as will cover it, till as much as possible of the nitre is dissolved; the liquor is then to be strained through a thick flannel bag, afterwards filtered through blotting-paper while hot, the sediment to be boiled down till a film rises on the surface; again filtered and set by to cool and crystallize, as directed in the process for the former method.
As the nitre must always be reduced to fine powder, previous to mixing it with othersubstances, this is easily done by dissolving it in a little more than its own weight of boiling water, keeping the solution over a gentle fire, and continually stirring it with a flat stick till all the water is evaporated, when the powder is to be taken out and dried before a gentle fire; during which, care must be taken not to let it remain too long, or exposed to too great a heat, otherwise it will be melted into a firm cake. The drying may be completed by suffering it to remain a sufficient time on paper before the fire. For the purification of salt-petre, both these methods may (by attending to the foregoing instructions,) be practised with success; but of the two, we would more strongly recommend the former.
2.Sulphur.—Sulphur is the next ingredient, in regard to importance, as being the most inflammable material we are acquainted with. It exists in three states, in all of which it is occasionally employed in fire-works; the first is that brought from the neighbourhood of volcanoes, and is callednative sulphur, but more commonlysulphur vivum, though (it may be observed,) what is sold in the shops under this name is a drossy powder, the refuse left after purification. The second is that in the roll, calledroll sulphur, orstone brimstone. The third is thesublimed sulphur, or as it is commonly calledflower of sulphur;this when genuine is the purest, and is found to answer best for all nice and delicate articles, and from its being already in a state of powder it is by far the most convenient, as the others require to be ground or mealed previous to their being used. The first kind is the cheapest, and answers pretty well for all large and coarse articles, but as it is most frequently mixed with earthy matter and other impurities, the use of it we would not very much recommend. The second is found to be the strongest, and which is mostly used, particularly for most of the ordinary articles; but such is the desire of gain, that this article of sulphur is not suffered to pass through the hands of dealers without its quality being reduced by adulteration, which they effect by mixing with it rosin, flour, &c.; when pure it is of a bright yellow colour, dense but not too heavy, easily cracks with the heat of the hand, and the broken parts look bright and crystallized. There is another kind ofsulphur(though not generally known among dealers) which does not burn like the others, and what is rather singular, it emits no sulphurous smell, for being put upon the fire it melts just like common wax; this sort is found in great abundance in Iceland near Mount Hecla, and Carniola. This sulphur is commonly of a reddish colour, like that found in the straitsof Heildesheim, where it is likewise of several colours, as pale yellow and green, and generally adheres to the surface of stone and rocks, from which it may be easily broken off and collected; that which is perfectly yellow of each kind is the best. That of our first description, orsulphur vivum, is sometimes calledquick sulphurfrom its undergoing no change by fire, since its productions by nature; and in some countries it is calledvirgin sulphur, because the women and girls in Campania frequently make a kind of paint of it, for no less delicate purpose than that of beautifying the face. Should either kind be met with in an impure state the following method may be applied for the purpose of purification.
3.To purify Sulphur.—Melt a quantity of it in an iron pan, by which means the earthy and metallic parts will be precipitated, and then pour it into a copper-kettle, where it will form another deposit of the impure matter with which it is mixed; after keeping it for some time in a melted state, pour it into cylindric wooden moulds, for the purpose of forming it into sticks; the moulds may be about an inch in diameter; their length may be various. If the sulphur should take fire during this operation it may be quickly extinguished by covering the pan close over at the top.
4.Charcoalis also a considerable ingredientin our compositions, but is of a much more simple nature than that of the foregoing ones. It may generally be procured at the hardware shops, or at foundries, or it may be easily prepared, for which put a quantity of small pieces of wood, such as beech or alder, into a large earthen or iron pot, filling up the vacuities, and covering the top with sand; then placing the pot in the middle of a strong fire, and keeping it at a red heat for two or three hours, as the sand excludes the air, the wood is thus reduced to charcoal without the possibility of its being consumed; and when the pot is cold, the charcoal is to be taken out and kept for use in some very dry place. Small quantities should only be made at a time, as it is always best newly prepared.
5.Steel-dustis another important ingredient in fire-works, for being mixed with mealed powder or some other composition, and the mixture inflamed in a proper tube, or case, the jet of fire produces a most brilliant appearance by the sparks arising from the ignition of the iron in the oxygen gas of the nitre.
Iron-filings, (for this Steel-dust is nothing more than pure iron reduced into small particles by filing or some other method,) when free from rust, and not mixed with any impurities, answer very well; but fire-workmakers generally prefer cast-iron reduced to powder, by beating thin plates of it on a cast-iron anvil with a heavy hammer, and sifting the broken particles through sieves of brass or iron wire, of different degrees of fineness, so as to separate the particles into grains of various sizes, according to the magnitude of the pieces. The grains thus sorted have been callediron-sand, and have been distinguished into sand of three or fourorders, according to their respective fineness; thus the sand that passes through the finest sieve, is called sand of thefirst order; and that which passes through the second, sand of thesecond order; and so on to the fourth, which is generally very coarse. The finest is calculated for fire-works of the smallest size, the second for pieces somewhat larger, and that of the last order, only for pieces of the largest size, such as gerbes of six or eight pounds, the composition of which being of proportionate strength to bring such large particles into a state of ignition.
As these grains are very apt to rust by keeping, they should be preserved either in close stopped bottles, well dried, or in boxes that shut close, and are lined with paper moistened in linseed oil. It sometimes happens that fire-works may be required to be kept a long time, or sent abroad; neither of which could be done with the brilliant fires,if made with filings unprepared, for this reason, that the salt-petre being of a damp nature it causes the iron to rust; the consequence of which is, that when the works are fired there will appear but very few brilliant sparks, but instead of them a number of red and drossy sparks; and besides, the charge will be so much weakened that if this were to take place in wheels, the fire would scarcely be strong enough to force them round; but to prevent such failures in the firing of them, the filings, or iron-sand, may be thus prepared:—
6.To prepare iron-sand.—Melt in a glazed earthen pan some brimstone over a slow fire, and when melted throw in some filings, which keep stirring till they are all covered with brimstone, this must be done while it is on the fire; then take it off and stir it very quickly till cold, when it must be rolled on a board with a wooden roller, till broken as fine as corned powder, after which sift from it as much of the brimstone as possible.
Second method.—There is another method of preserving filings so as to keep two or three months in winter, which is done by rubbing them between strong brown paper, which has been previously moistened with linseed oil. In heating the brimstone the caution given in Article 3, must be observed in the event of its catching fire.
We must observe in fine on this article, that it will be well to anticipate a little trouble in the preparation of this granulated Iron-sand, for cast-iron being of so hard a nature as not to be cut by a file, we are obliged to pulverize it, or reduce it to grains by the method we have described, which is rather difficult to perform; but when we consider what beautiful sparks this iron yields, no pains should be spared to granulate such an essential material.
We must further observe, that when these plates of iron cannot be procured, an old cast-iron pot may be employed; but especial care must be taken that its surface be perfectly free from rust and other impurities previous to its being pulverized, otherwise it will entirely destroy the effect it is intended to produce.
It is to the Chinese we are indebted for this method of rendering fire so brilliant and variegated in its colours, who discovered it long before Father d’Incarville made it known to the European countries. This sand, when it inflames, emits a light exceedingly vivid; and it is surprising to see fragments of this matter not larger than a poppy seed, form all of a sudden luminous flowers of stars, twelve and fifteen lines in diameter. These flowers are also of different forms, according to that of the inflamed grain, andeven of different colours, according to the matters with which the grains are mixed. But rockets, into which this composition enters, cannot be long preserved, unless prepared as described in the early part of this article.
There are many other substances occasionally employed in the composition of fire-works, but as they can be procured at all Chemists and Druggists ready for the purpose, we consider it unnecessary to give any detail respecting them, further than enumeration. They are chiefly the following, viz.Camphor, which is used to improve the appearance of the fire;Antimony, orSulphuret of Antimony,Sal-ammoniac,Verdigrease, andPitch, for giving to the fire different and particular shades of colour;Flowers of Benjamin, orBenzoic-acid, for imparting to it an agreeable odour; andSpirits of Wine, orCamphorated Spirits, for mixing up the ingredients into a paste. These liquids are found to answer much better than common water, or gum-water, which is sometimes used, as they do not dissolve the salt-petre, and are therefore not so liable to produce a separation of the materials employed.Lamp-blackis sometimes used instead of charcoal, and is supposed to have the effect of diminishing the heat of the fire, while it does not materially lessen its brilliancy. Thence it isa considerable ingredient in what is calledcold-fire, theseeming paradox ofwhich we shall hereafter reconcile. For the same purpose, that of diminishing the force of the composition,powdered glassandsaw-dusthave been frequently employed; but probably these effects might be better, and with more certainty answered, by lessening the proportion of nitre.
7Oil of Camphor.—This liquid is frequently used for the purpose of moistening the compositions; it is thus easily procured: put a small quantity of Camphor into a brass mortar, and to it add some oil of sweet almonds, sufficient to reduce it to a stiff paste, then work the mixture well together, and it will turn to a green colour, after which add a sufficient quantity of oil to liquify it for use. We must observe on the use of this liquid, that the composition into which it enters must be kept as much as possible from the air, as an exposure to it will cause it to evaporate, and thereby cause a failure in the exhibition.
8.Benzoin.—Benzoin, or as it is vulgarly called Benjamin, is a resinous matter obtained from the tree calledBenzoin, and is brought from different parts of the Indies, where it is found of various kinds, and of different colours; the best is that which is full of white spots and is easily broken. It is used inodoriferous fire-works, but prior to which it must be reduced to a fine powder, which may be effected by the following method:—put about three or four ounces of Benzoin grossly pounded into a deep and narrow earthen pot, and cover the pot over with a cone of thick paper, which tie closely round the edge, then place the pot over the fire and apply a moderate heat; after the interval of an hour take off the cone, and you will find some flower sticking to the under-side of it; or in the language of chemistry, the acid is sublimed and is deposited on the paper; the cone must be returned to the pot, and the operation continued till the flower appears very white and fine.
The acid which is frequently used may be obtained by digesting Benzoin in sulphuric acid, and by this it is obtained much purer and in finer crystals than by any other method.
On this article we deem it requisite to give the above information; but to the private practitioner, it will be more eligible to purchase it ready prepared.