This section is from the book "The Manufacture Of Liquors, Wines, And Cordials, Without The Aid Of Distillation", by Pierre Lacour. Also available from Amazon: Manufacture of Liquors, Wines, and Cordials, Without the Aid of Distillation.
A bead is composed of one or more small white globules, found floating on the surface of any liquid that has been subject to agitation, and is supposed to denote the strength of liquors; for instance, if a portion of spirit be subjected to a brisk agitation for a moment in a tumbler, or proof glass, and the bubbles continue on the surface for a few minutes, it is called proof spirit; but if, on a discontinuance of the agitation, the bubbles disappear, the spirit is said to be below proof.
A bead can be given to spirits from three sources; first, from alcohol, which may be known from the globules being of the size of a duck shot; the second source is from filtering the liquid through any sub stances that may contain mucilage, or starch. This bead may be known from its magnitude, being twice and thrice that of the alcoholic bead, and also their great tenacity, by continuing for some time after the agitation has ceased; and when the exciting substance, viz. mucilage or starch, is added to excess, the surface of the spirit will be covered with these globules.
The distinguishing feature of this bead is the great magnitude of its globules, which greatly exceed any others.
The bead derived from the third source is a chemical compound, resulting from the combination of sweet oil and oil of vitriol; say by mixing drop by drop, twenty drops sulphuric acid, with thirty drops sweet oil; this quantity is used to give a bead to ten gallons of spirit. This quantity, in some instances, may not suffice, as the spirit may contain some incompatibles; in this case the mixture may be added until the proper bead can be seen by agitation. This bead may be distinguished by the globules bearing a strong resemblance to the frothy productions of soap: they are small, frothy, and white, lying compact, or closely knit together, on the surface of the liquid.
The above beading mixture should only be prepared when required, as it does not improve by age. To prevent a failure in the above preparation, owing to adulterated sweet oil being used, which has De-come so plentiful in market, any oil that will stand the following test, will answer: mix equal portions of nitric acid and sweet oil; if the margins of this mixture should become a yellowish or yellowish green color, the oil is pure.
Alum, alkalies, and acids, in solution, are all incompatible with the beading mixture.