The Cultivation of The Native Grape, and Manufacture of American Wines

by George Husmann

"If a solution of 1,369 per cent, of caustic ammonia is added to this red fluid, and the tube is turned around to effect the necessary mixture, keeping its mouth closed with the thumb, after the addition of more or less of the ammonical fluid, it will change into violet. This tinge indicates the saturation of the acids, and the height of the fluid in the tube now shows the quantity of acid in the must, by whole, half and fourth parts per cent. The lines marked 1, 2, 3, 4, indicate whole per cents.; the short intermediate lines, one-fourth per cents."

When Dr. Gall, shortly before the vintage of 1850, first publicly recommended the dilution of the acids, he was obliged to refer to this instrument, as already known, and everywhere at hand, which was at the same time cheap, and simple in its use. "It is true, however, that if must is examined by this instrument, the quantity of acids contained in it, is really somewhat larger than indicated by the instrument; because the acids contained in the must require for their saturation a weaker solution of ammonia than acetic acid." As however, Otto's acidimeter shows about one eighth of the acids less than the must actually contains, and about as much acids combined with earths is removed during fermentation, Dr. Gall recommends that the quantity of acids be reduced to 6½, or at most 7 thousandths of Otto's acidimeter, and the results have shown that this was about the right proportion; as the wines in which the acids were thus diluted were in favor with all consumers.

"The acidimeter referred to was afterwards improved, by making the tube longer and more narrow, and dividing it into tenths of per cents, instead of fourths; thus dividing the whole above 0 into thousandths. But although by this improved acidimeter the quantity of acids could be ascertained with more nicety, there remained one defect, that in often turning the glass tube for mixing the fluids, some of the contents adhered to the thumb in closing its mouth. This defect was remedied in a new acidimeter, invented by Mr. Geisler, who also invented the new vaporimeter for the determination of the quantity of alcohol contained in wine. It is based on the same principle as Otto's, but differs altogether in its construction. It is composed of three parts, all made of glass; the mixing bottle, Fig. 34; the Pipette, Fig. 35; and the burette, Fig 36. Besides, there should be ready three small glasses—one filled with tincture of litmus, the second with a solution of 1,369 per ammonia, and the third with the must or wine to be tested; also, a taller glass, or vessel, having its bottom covered with cotton, in which glass the burette, after it has been filled with the solution of ammonia, is to be placed in an upright position until wanted.

Fig. 34. Fig. 35. Fig. 36.

"To use this instrument the must and the tincture of litmus, having first received the normal temperature of 14° Reaumer, are brought into the mixing bottle by means of the pipette, which is a hollow tube of glass, open on both ends. To fill it, place its lower end into the tincture or must, apply the mouth to the upper end, and by means of suction fill it with the tincture of litmus to above the line indicated at A. The opening of the top is then quickly closed with the thumb; by alternately raising the thumb, and pressing it down again, so much of the tincture is then allowed to flow back into the glass so as to lower the fluid to the line indicated at A. The remainder is then brought into the bottle, and the last drops forced out by blowing into the pipette.

"In filling it with must, raise the fluid in the same way, until it comes up to the line indicated at B, and then empty into the mixing bottle.

"The burette consists of two hollow tubes of glass. In filling it, hold the smaller tube with the right hand into the glass containing the solution of ammonia, apply the mouth to the larger one, and by drawing in the fluid the tube is filled exactly to the line indicated at 0 of the tube.

"Holding the mixing bottle by the neck between the thumb and forefinger of the left hand, place the smaller tube of the burette into the mouth of the mixing bottle, which must be constantly shaken; let enough of the solution of ammonia be brought drop by drop, into the mixture in the bottle, till the red has been changed into the deep reddish blue of the purple onion. This is the sign of the proper saturation of the acids. To distinguish still better, turn the mixing bottle upside down, by closing its mouth with the thumb, and examine the color of the fluid in the tube-shaped neck of the bottle, and afterwards, should it be required, add another drop of the ammonia. Repeat this until the proper tone of color has been reached, neither red nor blue. After thus fixing the precise point of the saturation of the acids, the burette is held upright, and the quantity of the solution of ammonia consumed is accurately determined,—that is, to what line on the scale the burette has been emptied. The quantity of the solution so used corresponds with the quantity of acids contained in the must—the larger division lines opposite the numbers indicating the thousandths part, and the smaller lines or dots the ten thousandths part.

"Until the eye has learned by practice to recognize the points of saturation by the tone of color, it can be proven by means of litmus paper. When the mixture in the bottle begins to turn blue, put in the end of a slip of litmus paper about half an inch deep, and then draw this end through your fingers, moistened with water. So long as the ends of the blue litmus paper become more or less reddened, the acids have not been completely saturated. Only when it remains blue, has the point of saturation been reached.