Twenty-five grams of ground malt are extracted with 500 c.c. of pure distilled water for three hours at 21.1°, and filtered. The first 100 c.c. of the filtrate are rejected. Of the perfectly bright residual filtrate, 3 c.c. are allowed to act on 100 c.c. of a 2 per cent. solution of soluble starch at 21.1° for an hour in a 200 c.c. flask.

1 J. Inst. Brewing, 1906, 12, 6.

Decinormal alkali (10 c.c.) is then added in order to stop further diastatic action, the liquid cooled at 155°, made up to 200 c.c. with distilled water at the same temperature, well shaken, and titrated against 5 c.c. portions of Fehling's solution, ferrous thio-cyanate solution being used as indicator.

The method of titration (Ling) is carried out in the following manner: -

Five c.c. of Fehling's solution (34.64 grams of crystallised copper sulphate, 70 grams of sodium hydroxide, and 175 grams of sodium potassium tartrate, per litre) are accurately measured into a 150 c.c. boiling flask, and raised to boiling over a small naked Bunsen flame. The converted starch solution is added from a burette, at first in small quantities of about 5 c.c, the mixture being kept rotated and boiled after each addition until reduction of the copper salt is complete, which is ascertained by rapidly withdrawing a drop of the liquid with a glass rod and bringing it at once in contacl with a drop of the indicator on a porcelain or opal glass slab. Then if x denotes the number of c.c. of the converted solution required to reduce the 5 c.c. of Fehling's liquid, and y the number of c.c. of malt extract contained in 100 c.c. of the same converted solution (200 c.c),

Diastatic power = 1000 / xy

A gravimetric method of determining diastatic activity has been proposed by Sherman, Kendall, and Clark,1 which they state is capable of greater accuracy than Lintner's method.

Soluble starch can be prepared by various methods. Lintner obtained it by allowing potato starch to remain in contact with 7 5 per cent, hydrochloric acid for seven or eight days. Brown and Morris, using 12 per cent, acid, obtained a similar product in twenty-four hours. Starch thus treated, and washed free from acid, dissolves in hot water without forming a viscid paste. To prepare it by Lintner's method for the foregoing determination, purified potato starch is mixed with about twice its weight of hydrochloric acid, sp. gr. 1037, at the ordinary temperature (15-18°), and allowed to act for seven days, stirring up every day. The acid is then poured off, the starch washed very thoroughly by decantation with water until free from acid, filtered on a Buchner filter, and drained as dry as practicable at the filter pump; then

1 .7. Amer. Chem. Sac, 1910. 32, 1082 spread on a new porous plate, and dried as quickly as possible at a temperature of about 43°. The starch is then triturated in a porcelain mortar and rubbed through a fine hair sieve. It is dissolved in boiling water in the proportion of 2 grams per 100 c.c, and cooled to 21.1° for use in the experiment as above described. The solution should not be gelatinous, should be neutral to litmus, and should show only a negligible reduction of Fehling's solution.

If the malt is found to have a diastatic power exceeding 50, less than 3 c.c. of the malt extract must be taken, and the experiment repeated.

Alternatively, the "Lintner value" of malt is often determined by a comparative series of test-tube experiments carried out as follows. Eight or ten clean test-tubes, of about 2 cm. internal diameter, are arranged in a stand suitable for placing in a water-bath. In each of the tubes 10 c.c. of the 2 per cent, solution of soluble starch are placed, and the temperature brought to 21.1° by immersing the stand in a bath kept at this temperature. Quantities of 01, 02, 03 . . . c.c. of the malt extract, prepared as already described, are run into the tubes, so that each tube receives 0 1 c.c. more than the preceding one. The time is noted, the contents of each tube well mixed, and all are kept in the bath at 211° for exactly an hour. At the end of this period 5 c.c. of Fehling's solution are mixed with the contents of each tube. The whole are then heated in a boiling water-bath for ten minutes, and allowed to settle. In the series of tubes there will usually be found some in which the sugar produced has been insufficient to reduce the whole of the Fehling's reagent, so that the supernatant liquid is blue; and also others in which the reduction is complete, and the liquid is colourless or yellow. In particular, two neighbouring tubes will be found, one showing under-reduction and the other exact reduction or over-reduction, from which the quantity, x, of malt extract just necessary for the reduction can be judged. Then, taking the diastatic power of 0 1 c.c. of malt extract (1 to 20) as 100, the diastatic power of the sample is given by 0.1 x 100 / x.

From this value 1.5 is deducted on account of reducing sugars in the extract.

An "iodine method" of determining diastatic power is described by Sherman, Kendall, and Clark.1

A standard starch paste is prepared by suspending a quantity of air-dry potato starch, equivalent to 10 grams of anhydrous starch, in 100 c.c. of cold water; this suspension is added to a quantity of water, sufficient to make up the total volume to 1 litre, which has meanwhile been heated nearly to boiling under a reflux condenser; then the whole is boiled for two hours under the condenser, and allowed to cool.

1 J. Amer. Chem. Soc, 1910, 32, 1073.

Portions of 250 grams of this standard paste (=25 grams of anhydrous starch) are placed in flasks of 350-400 c.c. capacity immersed in a water-bath kept at 40°, and the desired amount of the enzyme preparation introduced together with 20 c.c. of water. The contents of the flask are well mixed, and digestion is continued at 40° until 025 c.c. of the mixture yields no coloration with 5 c.c. of a standard dilute iodine solution. Tests are made with varying amounts of the enzyme solution until that amount is found which completes the conversion in 30 minutes (+ 1 minute).

The diastatic power is expressed as the weight of starch (2 5 grams) divided by the weight of enzyme preparation required to digest it under the prescribed conditions.

The iodine solution is prepared by dissolving 2 grams of iodine and 4 grams of potassium iodide in 250 c.c. of water, and diluting 2 c.c. of this solution to 1 litre.

The values obtained are, very roughly, about three times the values given by Lintner's method.