Chap. IV Of Borax
Process
To decompose Borax by the means of Acids, and to separate from it the Sedative Salt by sublimation and by crystallization.
Reduce to a fine powder the Borax from which you intend to extract the Sedative Salt. Put this powder into a wide-necked glass retort. Pour upon it an eighth part of its weight of common water, to moisten the powder; and then add concentrated Oil of Vitriol to the weight of somewhat more than a fourth part of the weight of Borax. Set the retort in a reverberatory, make a moderate fire at first, and augment it gradually till the retort become red-hot.
A little phlegm will first come over, and then with the last moisture that the heat expels the Sedative Salt will rise; by which means some of it will be dissolved in this last phlegm, and pass therewith into the receiver; but most of it will adhere in the form of saline flowers to the fore-part of the neck of the retort, just where it is clear of the groove of the furnace. There they collect into a heap, which the succeeding flowers push insensibly forward till they slightly stop the passage. Those which rise after the neck is thus stopped stick to the after-part of it which is hot, vitrify in some measure, and form a circle of fused Salt. In this state the flowers of the Sedative Salt seem to issue out of the circle, as from their basis: they appear like very thin, light, shining scales, and must be brushed off with a feather.
At the bottom of the retort will be left a saline mass: dissolve this in a sufficient quantity of hot water; filter the solution in order to free it from a brown earth which it deposites; set the liquor to evaporate, and crystals of Sedative Salt will form in it.
OBSERVATIONS.
Though Borax is of great use in many chymical operations, especially in the fusion of metals, as we shall have occasion to see, yet, till of late years, Chymists were quite ignorant of its nature, as they still are of its origin; concerning which we know nothing with certainty, but that it comes rough from the East Indies, and is purified by the Dutch.
M. Homberg was one of the first that attempted to analyse this Salt. He shewed, that on mixing it with the Vitriolic Acid, and distilling the mixture, a salt sublimes in little fine needles. This product of Borax he called by the name of Sedative Salt, because he found it had the property of moderating the great tumult and heat of the blood in fevers.
After M. Homberg, other Chymists also exercised themselves on Borax. M. Lemery discovered that the Vitriolic is not the only Acid by means of which the Sedative Salt may be obtained from Borax; but that either of the other two Mineral Acids, the Nitrous or the Marine, may be used in its stead.
M. Geoffroy hath greatly facilitated the means of obtaining the Sedative Salt from Borax; having shewn that it may be extracted by crystallization as well as by sublimation; and that the Sedative Salt so obtained is in no respect inferior to that which was procured before by sublimation only. To him also we are indebted for the discovery, that in the composition of Borax there is an Alkaline Salt of the same nature as the basis of Sea-salt. This he found by observing that he got a Glauber’s Salt from a solution of Borax into which he had poured some Vitriolic Acid with a view to obtain its Sedative Salt.
Lastly, M. Baron, whom we mentioned before on occasion of this Salt, hath proved, by a great number of experiments, that a Sedative Salt may be procured from Borax by the help of Vegetable Acids, which was never done by any body before him; that the Sedative Salt is not a combination of an Alkaline matter with the Acid made use of in extracting it, as some of its properties seemed to indicate; but that it exists previously and completely formed in the Borax; that the Acid employed to extract it only helps to disengage it from the Alkali with which it is united; that this Alkali is actually of the same nature as the basis of Sea-salt, because that after extracting the Sedative Salt, which by its union therewith forms the Borax, a Neutral Salt is found, of the same sort with that which would be produced by combining the basis of Sea-salt with the particular Acid made use of; that is, if with the Vitriolic Acid, a Glauber’s Salt; if with the Nitrous Acid, a quadrangular Nitre; and if with the Marine Acid, a true Sea-salt; and, lastly, that the Sedative Salt may be re-united to its Alkali, and reproduce a Borax.
Nothing therefore now remains, to give us all the insight we can desire into the nature of Borax, but to know what the Sedative Salt is. M. Baron hath already given us certain negative notices concerning it, by shewing what it is not; that is, that the Acid employed in its extraction doth not enter into its composition. We have great reason to hope, that he will carry his inquiries still further, and clear up all our doubts on this subject.
The Sedative Salt may be extracted from Borax, not only by the means of pure and simple Acids, but also by the same Acids combined with a metallic basis. Thus Vitriols, for instance, may be employed for this purpose with good success. It is easy to see, that the Vitriol must be decomposed on this occasion, and that its Acid cannot unite with the Alkali in which the Sedative Salt is lodged, without quitting its metallic basis, which must of course precipitate.
The Sedative Salt actually sublimes, when a liquid containing it is distilled; but it does not therefore follow, that it is naturally volatile. It rises only by the aid of the water with which it is mixed. The proof of this assertion is, that, when all the humidity of the mixture containing this Salt is dissipated, no more Salt will rise, be the fire ever so violent; and that by adding more water to moisten the dried mass containing it, more Salt will every time be obtained, through many repeated distillations. In the same manner, if some Sedative Salt be moistened, and exposed to a proper degree of heat, a small quantity thereof will rise at first by the help of the water; but as soon as it grows dry it remains exceedingly fixed. This observation we owe to M. Rouelle.
The Sedative Salt hath the appearance and the taste of a Neutral Salt: it does not change the colour of the juice of violets; nor does it easily dissolve in water; for it requires a quart of boiling water to dissolve two ounces of it: yet, with regard to Alkalis, it has the properties of an Acid; it unites with those salts, forms therewith a saline compound which crystallizes, and even expels the Acids that happen to be combined with them; so that it decomposes the same Neutral Salts that are decomposed by the Vitriolic Acid.
The Sedative Salt, when suddenly exposed to the violent heat of a naked fire, loses near half its weight, melts, puts on and retains the appearance of glass; but its nature still remains unchanged. This glass dissolves in water, and shoots anew into crystals of Sedative Salt. This Salt communicates to the Alkaline salt with which it is united, when in the form of Borax, the property of melting with a moderate heat, and forming a kind of glass; and it is this great fusibility that recommends the frequent use of Borax as a flux for assaying ores. It is also employed sometimes as an ingredient in the composition of glass; but, in time, it always communicates thereto the fault which its own glass hath, namely that of tarnishing with the air. The Sedative Salt hath, moreover, the singular property of dissolving in Spirit of Wine, and of giving to its flame, when set on fire, a beautiful green colour. All these observations we owe to Mess. Geoffroy and Baron.
M. Geoffroy prepares the Sedative Salt by crystallization only, in the following manner. “He dissolves four ounces of refined Borax in a sufficient quantity of warm water, and then pours into the solution one ounce and two drams of highly concentrated Oil of Vitriol, which makes a crackling noise as it falls in. When this mixture has stood evaporating for some time, the Sedative Salt begins to make its appearance in little, fine, shining plates floating on the surface of the liquor. The evaporation is then to be stopped, and the plates will by little and little increase in thickness and breadth. They unite together into little tufts, forming with each other sundry different groups. If the vessel be ever so little stirred, the regularity of the crystals will be disturbed; so that it must not be touched till the crystallization appears to be finished. The crystalline clusters, being grown too bulky and too heavy, will then fall of themselves to the bottom of the vessel. This being observed, the saline liquor must be gently decanted from those little crystals, which, as they are not easily dissolved, must be washed clean, by pouring cold water slowly on the sides of the pan, three or four times successively, in order to rinse out all remains of the saline liquor, and then set first to drain, and afterwards to dry in the sun. This Salt, in the form of light flakes of snow, is now soft to the touch, cool in the mouth, slightly bitter, crackling a little between the teeth, and leaving a small impression of acidity on the tongue. It will keep long without giving or calcining, if managed according to the preceding directions; that is, if it be exactly freed from its saline liquor.
“It differs from the Sedative Salt obtained by sublimation in this respect only, that notwithstanding its seeming lightness it is a little heavier than the other. M. Geoffroy supposes the cause of this weight to be, that, as several of the thin plates adhere together in crystallizing, they retain between them some small matter of humidity; or, if you will, that, as they form larger crystals, they present less surface to the air which elevates light bodies: whereas, on the contrary, the other Sedative Salt, being driven up by the force of fire, rises into the head of the cucurbit in a more subtile form, having its particles much more expanded and divided.
“M. Geoffroy, having put his Sedative Salt made by crystallization to all the same trials with that made by sublimation, satisfied himself that there is no other difference between the two. If the Sedative Salt made by crystallizations happens to calcine in the sun; that is, if its lustre tarnishes, and its surface grows mealy, it is a sign that it still contains either a little Borax or some Glauber’s Salt: for these two Salts are apt to calcine in this manner, and pure Sedative Salt should not be subject to this inconvenience. In order to purify it, and free it entirely from those Salts, it must be dissolved once more in boiling water. As soon as the water cools, the Sedative Salt reappears in light, shining, crystalline plates, swimming in the liquor. After standing four and twenty hours, the liquor must be decanted, and the salt washed with fresh water; by which means it will be very pure and beautiful.”
Glauber’s Salt and Borax dissolve in water with vastly more ease than the Sedative Salt, and consequently do not crystallize so readily by much: so that the small portion of those salts which may have been left on the surface of the Sedative Salt, being diffused through a large quantity of water, continues in a state of solution, while the Sedative Salt crystallizes; which being also washed afterwards with fair water, it is impossible that the smallest particle of those other Salts should remain adhering to it; and consequently this must be deemed an excellent way of purifying it.