SECTION I.OF FIRE.
Thoughfire is the chief cause and principle of almost every change in bodies, and though persons untaught in chymistry imagine they understand its nature, yet, certain it is, few subjects are so incomprehensible, or elude so much our nicest research. The senses are very inadequate judges of it; the eye may be deceived, and suppose no fire in a bar of iron, because it does not appear red, though at the same time it may contain enough to generate pain: the touch is equally unfaithful, for a body, containing numberless particles of heat, will to us feel cold, if it is much more so than ourselves.
The great and fundamental difference among philosophers, in respect to the nature of fire, is, whether it be originally such, formed by the Creator himself, at the beginning of things; or whether it be mechanically producible in bodies, by inducing some alteration in the particles thereof. It is certain that heat may be generated in a body, by attrition; but whether it existedthere before, or was caused immediately by the motion, is a matter of no great import to the art of brewing; for the effects, with which we are alone concerned, are the same.
Fire expands all bodies, both solid and fluid. If an iron rod just capable of passing through a ring of the same metal, is heated red-hot, it will be increased in length, and so much swelled as not to be able to pass through the ring, as before:2if a fluid is put into a bellied glass, with a long slender neck, and properly marked, the fluid, by being heated, will manifestly rise to a considerable height.
The expansion of fluids, by heat, is different in different fluids; with some exceptions, it may be said to be in proportion to their density. Pure rain water, gradually heated to ebullition, is expanded one 26th part of its bulk,3so that 27 gallons of boiling water, will, when cold, measure no more than 26, and 27 gallons of boiling wort will not yield so much, because worts contain many oily particles, which, though less dense than water, have the property of being more expansible: hence we see the reason why a copper, containing a given number of barrels of wort, when cold, is not capable to hold the same of beer, when boiling.
Bodies are weakened or loosened in their texture by fire: the hardest, by an increased degree of heat, will liquify and run; and vegetables are resolved and separated by it into their constituent parts. It must be owned vegetables seem at first, on being exposed to the fire, to become rigid or stiff; but this is owing to the evaporation of the aqueous particles, which prevented a closer adhesion of the solid matter. It is only in this manner fire strengthens some bodies which before were weak.
That the texture of bodies should be loosened by fire, seems a consequence of expansion; for a body cannot be expanded but by its particles receding farther from one another; and if these be not able to regain the situation they had when cold, the body will remain looser in its texture than before it suffered the action of fire. This is the case of barley when malted.
Fire may be conveyed through most bodies, as air, water, ashes, sand, &c. The effect seems to be different according to the different conveyances. A difference appears between boiling and roasting, yet they answer the same purpose, that of preserving the subject; and this, in proportion to the degree of heat it has suffered. A similar variety appears, even to our taste, from thedifferent conveyance of fire to malt: for acids having a great tendency to unite with water, if this element does not naturally contain any itself, is the reason why a great heat is conveyed through water, and applied to extract the virtues of pale malt; the water gaining from the grain some of these salts, or possessing them itself, the effect of this great aqueous heat is not to imprint on the palate a nauseous burnt taste, as is the case of great heats, when conveyed through air to the same grain. The salts the water has obtained, or perhaps had, being sheathed by the oils it draws from the malt, rather become saccharine, which cannot be the case when oils are acted upon by a strong heat, entirely void of any such property; but malt, the more it is dried, the longer is it capable of maintaining itself in a sound state, and the liquor brewed with it will, in proportion to its dryness, keep the longer sound, the hotter the water is, applied to malt, provided its heat doth not exceed the highest extracted degree, the more durable and sound will the extract be.
The last consideration of fire or heat, relative to brewing, is the knowledge of its different degrees, and how to regulate them. Till of late, chymists and all others, were much to seek in this respect; they distinguished more or less fire in a very vague and indeterminate manner, as the first, second, third, and fourth degree of heat, meaning no precise heat, or heat measured by any standard; but, by the invention of the thermometer, weare enabled to regulate our fires with the utmost precision. Thermometers are formed on different scales; and therefore, when any degree of heat is mentioned, in order to avoid confusion, the scale made use of should be indicated. I have constantly employed Fahrenheit’s, as it is the most perfect, and the most generally received. According to this instrument,4by the author of it, an artificial cold was made so as the mercury stood at 72 divisions below the first frost. The gentlemen of the French Academy, in the winter of the year 1736, observed, at Torneao, Latitude 65° 51´, the natural cold to be 33 degrees below 0: these are proofs there are colds much more intense than the first frost, or 32 degrees, where water first begins to harden into ice; from 32 to 90 degrees are the limits of vegetation, according to the different plants that receive those or the intermediate heats. The 40th degree is marked by Boerhaave as the first fermentable heat, and the 80th as the last: 47 degrees I have found to be generally the medium heat of London, throughout the year, in the shade; 98 degrees is said to be that of our bodies when in health, as from 105 to 112 are its degrees when in a fever. Hay stacked with too much moisture, when turned quite black, in the heart of the rick, indicated a heat of 165 degrees. At 175 the purest and highest-rectified spirits of wine boil, and atthis degree I have found well-grown malts to charr, at 212 degrees water boils, at 600 quicksilver and oil of vitriol. Gold, silver, iron, and most other metals in fusion exceed this heat; greater still than any known is the fire in the focus of the burning lens of Tschirnhausen, or of the concave mirror made by Villette; they are said to volatilise metals and vitrify bricks. Thus far experiments have reached; but how much more, or how much less, the power of this element extends, will probably be forever hid from mankind.