and Duell was proposed by Rodewald." The determination of the molecular weight was accomplished by means of the lowering of the vapor pressure of water. The calculated value was 4370, equivalent to (C6H10O5) 27; the correct weight for this formula is 4374.

This reduction in size of the proposed molecular weight of starch was reversed, however, two years later by Friedenthal,12 who dissolved a commercial soluble starch (called ozone starch) in water and reprecipitated it with alcohol. This product showed, by the freezing-point method, a molecular weight of 9450, which, according to Friedenthal, corresponds with the formula

(C6H10O5)60

In 1899, Brown and Millar13 presented the results of several years of further work upon the hydrolytic products of starch. The main feature of their paper was the discovery of a reducing dextrin to which they gave the formula 39 (C6H10O5) + (C6H12O6), or 40(C6H10O5) + H2O. As the empirical formula indicates, it might be made up by the condensation of forty glucose molecules with the elimination of thirty-nine molecules of water, in accord with the appended structural formulas:

The ordinary combustion method would fail to reveal the pres

ence of one H2O-group in a molecule of this size. This difficulty was surmounted by the oxidation of this dextrin by mercuric oxide to a dextrinic acid, which, in turn, was precipitated by lime to form the calcium salt. This salt contained the theoretical amount of calcium, 0.3 percent; and, upon hydrolysis, yielded the correct amount of glucose. As previously mentioned, the earlier work of Brown and Heron resulted in the suggestion of the equation,

10 C12H20010 + 8H2O→8 C12H22O11 + 2 C12H20010,

Maltose

as a correct representation of hydrolytic changes.

Dextrin

Inasmuch as this newly discovered dextrin could not be represented by a formula simpler than 40 C6H10O5 + H2O, it was necessary to modify the above equation to allow for it, as follows:

If this equation holds, then the starch molecule must be at least five times the size of the dextrin molecule. Now, the molecular weight of the dextrin is 6498 or 6480 + 18; therefore, the weight of the starch molecule is at least 32,400, equivalent to (C6H10O5)200. (In 1889 Brown and Morris had found that the freezing-point method indicated a molecular weight, for soluble starch, of about 20,000 to 30,000.)

Since starch is non-reducing it has no free carbonyl group and, hence, the simplest manner, to quote Brown and Millar, "to express its constitutional form with due regard to all facts is to consider it made up of the residues of eighty maltan and forty dextran groups linked in a ring form by means of oxygen atoms. On hydrolysis the dextran complex is split off with the formation of stable dextrin, whilst the maltan part of the ring is attacked at the oxygen linkings of the C12 groups, hydrogen ions of reacting water moving in one direction and hydroxyl ions in another, thus forming by successive stages of hydrolysis, maltodextrins and maltose."

This reasoning seems to be logical and, if the experimental results have been correctly interpreted, the starch molecule may be correctly represented by their proposed configuration (Fig. 1):

This structure has lately been attacked by Ling, who claims that the hydrolysis of starch by malt diastase does not produce eighty percent of maltose; maltodextrins being present. This statement, however, due to the great amount of evidence in favor of the production of eighty percent of maltose by the action of malt enzyme on starch, is open to question. Ling prefers to regard the starch formula as (C6H10O5)n - (n-1 H2O), similar to the (C6H10O5)n + H2O proposed by Kiliani, inasmuch as he considers carbohydrates to be derived from monoses by a series of condensations with the elimination of water. This view is at the present time quite general. As the proposed starch structure of Brown and Millar does not allow for this one molecule of water, their formula may, of course, possess other weak points.

In the year previous to the publication of the last mentioned work there appeared a paper by Johnson16 in which he proposed a molecular formula for starch. Experimental evidence is lacking,

the structure being the result wholly of hypothesis. The author says that the schema was intended to convey, only in a figurative manner, the probable nature of the starch molecule. The formula is based upon the fact that starch must be a multiple of (C6H10O5) 4, these groups being arranged as follows:

FIG. 2. Proposed structural formula for starch (Johnson).

To use Johnson's own words, - "As is seen, two dextrose molecules condense in a secondary group (HC.OH HO.CH) whilst the maltose molecules condense in the primary group (H2C.OH HO.CH2), the former becoming HC.O-CH and the latter H2C.O-CH2. The two aldehyde groups of the original dextrose molecules condense in the amylin groups as is shown above. This explains the non-reducing character of the starch."

The suggested condensation of "primary" and "secondary" OH groups in each sugar molecule has no experimental justification. In my opinion it does not seem necessary to assume polymerization of the aldehyde groups to explain the non-reducing character of starch. The disaccharide sucrose is not a reducing sugar, yet we do not assume that the aldehyde groups of the constituent monoses polymerize with one another.

The latest attempt to construct a starch molecule, and probably the most painstaking of any previous hypothesis, was brought out by Synkiewski" in 1902. His work consisted in studying the products of hydrolysis of starch by infusions of malt, with exhaustive investigation of the properties of the several dextrins isolated therefrom. The starting point in his work was the isolation of two dextrins, one called by him "protodextrin I" which was formed by hydrolyzing starch at ordinary temperature; and another, called "protodextrin II," which was formed by the hydrolysis of starch at 78° C.

The preparation of protodextrin II was accomplished by allowing malt extract to act on starch at about 78° C. until all starch was hydrolyzed. The dextrin was then separated by evaporation of the water, extraction with dilute alcohol to remove soluble carbohydrate, and final precipitation with strong alcohol. The product was a white amorphous powder which, after ultimate analysis and by determination of the depression of the freezing point of water, showed a molecular weight and structure equivalent to C36H62031 or (C6H10O5)6 + H2O. This is similar to the formula for the