Malt, when dried, has its oils made tenacious, in proportion to the power of heat it has been affected with; the grain, though ground, if the water for the extraction is not at least as hot as what occasioned this tenaciousness, must remain in great measure undissolved in the first extract, and deposit itself as just now was mentioned. 2. _The first extract should always have some froth or head in the underback._ The oils and salts of the malt, being duly mixed, form a saponaceous body, the character of which is that, on being shook, it bears a froth on its surface. 3. _The head or froth in the underback appearing red, blue, purple, or fiery, shews the liquors to have been taken too hot._ The hotter the water is, when applied to the malt, the more must the extract abound with oils, and consequently be more capable to reflect colors in a strong manner. But how precarious this method of estimating the quality of an extract is, in comparison to that which the thermometer affords, will appear from the following observation of Sir Isaac Newton: “Saponaceous bubbles will, for a while, appear tinged with a variety of colors, which are agitated by the external air, and those bubbles continue until such time as, growing excessive thin, by the water trickling down their sides, and being no longer able to retain the enclosed air, they burst.” Now as these bubbles vary in their density, in proportion to their duration, the colors they reflect must continually change, and therefore it is not possible to form an accurate judgment of the condition and saponaceousness of the extracts, by the appearance of their froth. 4. _When the grist feels slippery, it generally is a sign that the liquors have been taken too high._ This appearance proceeds from an over quantity of oil being extracted, and is the effect of too much heat. 5. _Beer ought always to work kind, out of the cask, when cleansed, but the froth, in summer time, will be somewhat more open than in winter._ The higher and hotter the extracting water is, the more oils doth it force into the must; when a wort is full charged with oils, the fermentation is neither so strong nor so speedy, and consequently the froth, especially the first, is thin, open, and weak. This improves as the liquor is more attenuated, and heat, which expands all bodies, must rarify the yeasty vesicles, the principal part of which is elastic air; but this open head, even in summer time, improves to one more kind, as the first, the most active period of fermentation, draws nearer to its conclusion. However vague and indeterminate these signs are, it would not be impossible to bring them to some degree of precision; but, upon the whole, this method would increase our difficulties, and yet, as to certitude, be inferior to the rules we have endeavoured to establish, we think it unnecessary to pursue any farther a research most likely neither entertaining nor useful. SECTION XVIII.