Principles and practice of agricultural analysis. Volume 3 (of 3), Agricultural products

Chapter IX: Preface: To Volume Third (9)

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The set solution of barium hydroxid must be preserved from contact with the carbon dioxid of the air. The burette should be directly attached to the bottle holding the set solution, by any of the usual appliances, and the air entering the bottle must be deprived of carbon dioxid. The water used in the work must be also free of air, and this is secured by boiling immediately before use.

_Example._—A sample of flour selected for the analysis weighed 3.212 grams. The starch was separated and reduced to paste in the manner described above. Thirty and four-tenths cubic centimeters of tenth-normal hydrochloric acid were exactly neutralized by ten cubic centimeters of the barium hydroxid solution. After treatment as above described, fifty cubic centimeters of the clear liquor, corresponding to ten cubic centimeters of the added barium hydroxid, required 19.05 cubic centimeters of tenth-normal hydrochloric acid. Then 30.4 - 19.05 = 11.35, and 11.35 x 5 = 56.75, which number corresponds to the total titration of the residual barium hydroxid in terms of tenth-normal hydrochloric acid. This number multiplied by 0.0324, _viz._, starch corresponding to one equivalent of barium, gave 1.8387 grams of starch or 57.24 per cent of the weight of flour employed.

The barium hydroxid method has been given a thorough trial in this laboratory and the results have been unsatisfactory when applied to cereals. The principle of the process, however, appears to be sound, and with a proper variation of working details, it may become practical.

=193. Disturbing Bodies in Starch Determinations.=—Stone has made a comparison of the standard methods of starch determinations, and the results of his work show that in the case of pure starch all of the standard methods give approximately correct figures. For instance, in the case of a pure potato starch, the following data were obtained:

By inversion with hydrochloric acid, 85.75 per cent; by inversion with oxalic and nitric acids, 85.75 per cent; by solution in salicylic acid, 85.47 per cent; and by precipitation with barium hydroxid, 85.58 per cent.[161]

When these methods are used, however, for the determination of starch in its original state, the widest variations are secured. Stone shows that these variations are due chiefly to the inverting effect of the reagents employed upon the pentosans present. In experiments made with pure xylan obtained from wheat straw, the methods employed gave from 44.73 to 67.16 per cent of material, which would be calculated by the usual methods as starch. Stone also shows that the pentosans are practically unaffected by the action of diastase or malt extract. Pure xylan treated with diastase, under the condition in which starch is converted into maltose and other soluble carbohydrates, fails to give any subsequent reaction whatever with alkaline copper solution. In all cases, therefore, where starch occurs in conjunction with pentose bodies, it is necessary to separate it by diastatic action before applying any of the methods of conversion of the starch into dextrose or its precipitation by barium hydroxid.

=194. Colorimetric Estimation of Starch.=—The production of the intensely blue color which starch gives with iodin has been used not only as the basis of a qualitive method, but also of many attempts at quantitive determination. These attempts have, as a rule, been attended with very unsatisfactory results, due both to the extraordinary delicacy of the reaction and to the fact that starches of different origin do not always give exactly the same intensity of tint when present in the same quantity. At the present it must be admitted that little should be expected of any quantitive colorimetric test.

In case such a test is desired the procedure described by Dennstedt and Voigtländer may be followed.[162] A weighed quantity of the starch-holding material, containing approximately half a gram of starch, is placed in a two liter flask and boiled with a liter of water. After cooling, the volume is completed to two liters and the starch allowed to subside. Five cubic centimeters of the clear supernatant liquor are placed in a graduated cylinder holding 100, and marked in half cubic centimeters. One drop of a solution of iodin in potassium iodid is added and the volume completed to the mark. A half gram of pure starch is treated in the same way and different measured portions of the solution treated as above until the color of the first cylinder is matched. From the quantity of pure starch in the matched cylinder the quantity in the sample is determined. The test should be made in duplicate or triplicate. If a violet color be produced instead of a blue, it may be remedied by treating the sample with alcohol before the starch granules are dissolved.

=195. Fixation of Iodin.=—In addition to forming a distinctive blue color with iodin, starches have the power of fixing considerable quantities of that substance. The starches of the cereals have this power in a higher degree than those derived from potatoes. In presence of a large excess of iodin the starches of rice and wheat have a maximum iodin-fixing power of about nineteen per cent of their weight. When only enough of iodin is employed to enter into combination the percentage absorbed varies from nine to fifteen per cent. The absorption of iodin by starches is a matter of importance from a general chemical standpoint, but as at present determined has but little analytical value. It is evident, however, that this absorption must take place according to definite chemical quantities and the researches of investigators may in the future discover some definite quantitive method of measuring it.[163]

=196. Identification of Starches of Different Origin.=—It is often important, especially in cases of suspected adulteration, to determine the origin of the starch granules. For this purpose the microscope is the sole resort. In many cases it is easy to determine the origin of the starch by the size or the shape and marking of the grains. In mixtures of more than one kind of starch the distinguishing features of the several starches can be clearly made out in most instances. There are, however, many instances where it is impossible to discriminate by reason of the fact that the characteristics of starch granules vary even in the same substance and from year to year with varying conditions of culture.

In many cases the illustrations of the forms and characteristics of starch granules which are found in books are misleading and no reliance can be placed on any illustrations which are not either photographs or drawings made directly from them. In the microscopic study of starches the analyst will be greatly helped by the following descriptions of the characteristic appearance of the granules and the classifications based thereon.[164]

=197. Vogel’s Table of the Different Starches and Arrowroots of Commerce.=—_A._ Granules simple, bounded by rounded surfaces.

I. Nucleus central, layers concentric.
_a._ Mostly round, or from the side, lens-shaped.
1. Large granules 0.0396-0.0528 mm, _rye starch_:
2. Large granules 0.0352-0.0396 mm, _wheat starch_:
3. Large granules 0.0264 mm, _barley starch_.

_b._ Egg-shaped, oval, kidney-shaped: Hilum often long
and ragged:
1. Large granules 0.032-0.079 mm, _leguminous starches_.

II. Nucleus eccentric, layers plainly eccentric or meniscus-shaped.
_a._ Granules not at all or only slightly flattened:
1. Nucleus mostly at the smaller end; 0.06-0.10 mm,
_potato starch_:
2. Nucleus mostly at the broader end or towards the
middle in simple granules; 0.022-0.060 mm, _maranta
starch_.

_b._ Granules more or less strongly flattened.
1. Many drawn out to a short point at one end.
_a._ At most 0.060 mm long, _curcuma starch_:
_b._ As much as 0.132 mm long, _canna starch_:
2. Many lengthened to bean-shaped, disk-shaped, or
flattened; nucleus near the broader end; 0.044-0.075 mm,
_banana starch_:
3. Many strongly kidney-shaped; nucleus near the edge;
0.048-0.056 mm, _sisyrinchium starch_:
4. Egg-shaped; at one end reduced to a wedge, at the other
enlarged; nucleus at smaller end; 0.05-0.07 mm,
_yam starch_:

_B._ Granules simple or compound, single granules or parts of granules, either bounded entirely by plain surfaces, many-angled, or by partly round surfaces.

I. Granules entirely angular.
1. Many with prominent nucleus: At most 0.0066 mm, _rice starch_:
2. Without a nucleus: The largest 0.0088 mm, _millet starch_:

II. Among the many-angled also rounded forms.
_a._ No drum-shaped forms present, angular form predominating.
1. Without nucleus or depression very small; 0.0044 mm,
_oat starch_:
2. With nucleus or depression; 0.0132-0.0220 mm.
_a._ Nucleus or its depression considerably rounded;
here and there the granules united into differently
formed groups; _buckwheat starch_:
_b._ Nucleus mostly radiate or star-shaped; all the
granules free; _maize_ (_corn_) _starch_:

_b._ More or less numerous kettledrum and sugar-loaf like forms.
1. Very numerous eccentric layers; the largest granules
0.022-0.0352 mm, _batata_ (sweet potato) _starch_:
2. Without layers or rings; 0.008-0.022 mm.
_a._ In the kettledrum-shaped granules the nucleal
depression mostly widened on the flattened
side; 0.008-0.022 mm, _cassava starch_:
_b._ Depression wanting or not enlarged.
_aa._ Nucleus small, eccentric; 0.008-0.016 mm,
_pachyrhizus starch_:
_bb._ Nucleus small, central, or wanting.
_aaa._ Many irregular angular forms;
0.008-0.0176 mm, _sechium starch_:
_bbb._ But few angular forms; some with
radiate, nucleal fissure; 0.008-0.0176 mm,
_chestnut starch_.

_C._ Granules simple and compound; predominant forms, oval, with eccentric nucleus and numerous layers; the compound granule made up of a large granule and one or more relatively small kettledrum-shaped ones; 0.025-0.066 mm, _sago starch_.

=198. Muter’s Table for the Detection of Starches when Magnified about 230 Diameters.=

[All measurements are given in decimals of an inch.]

_Group I_: All more or less oval in shape and having both hilum and rings visible.

_Group II_: With strongly developed hilum more or less stellate.

_Group III_: Hilum and rings practically invisible.

_Group IV_: More or less truncated at one end.

_Group V_: All granules more or less polygonal.

=199. Blyth’s Classification.=—Blyth gives the following scheme for the identification of starch granules by their microscopic appearance.[165]

_Division I.—Starches showing a play of colors with polarized light and selenite plate_:

The hilum and concentric rings are clearly visible, and all the starch granules, oval or ovate. Canna arrowroot, potato, arrowroot, calumba, orris root, ginger, galangal and turmeric belong to this division.

_Division II.—Starches showing no iridescence, or scarcely any, when examined by polarized light and selenite_:

Class I.—The concentric rings are all but invisible, and the hilum stellate. The bean, pea, maize, lentil, dari and nutmeg starches are in this class.

Class II.—Starches which have both the concentric rings and hilum invisible in the majority of granules: this important class includes wheat, barley, rye, chestnut, acorn, and many starches in medicinal plants.

Class III.—All the granules are truncated at one end. This class includes sago, tapioca and arum, several drugs and cinnamon and cassia.

Class IV.—In this class all the granules are angular in form and it includes oats, tacca, rice, pepper and ipecacuanha.

=200. Preparation of Starches for Microscopical Examination.=—The approximately pure starches of commerce may be prepared for microscopic examination by rubbing them up with water and mounting some of the suspended particles by one of the methods to be described below.

In grains, seeds and nuts the starch is separated by grinding with water and working through fine linen. The starch which is worked through is allowed to subside, again beaten up with water if necessary and the process continued until the grains are separated sufficiently for microscopic examination. A little potash or soda lye may be used, if necessary, to separate the granules from albuminous and other adhering matter. The analyst should have a collection of samples of all common starches of known origin for purposes of comparison.

The granules are mounted for examination by plain light in a medium of glycerol and camphor water. When polarized light is used the mounting should be in Canada balsam.[166] The reader can find excellent photomicrographs of the more common starches in Griffith’s book.[167]

=201. Appearance in Balsam with Polarized Light.=—Mounted in balsam the starches are scarcely visible under any form of illumination with ordinary light, the index of refraction of the granules and the balsam being so nearly alike. When, however, polarized light is used the effect is a striking one. It is very easy to distinguish all the characteristics, except the rings, the center of the cross being at the nucleus of the granule.

With the selenite plate a play of colors is produced, which is peculiar to some of the starches and forms the basis of Blyth’s classification.

=202. Description Of Typical Starches.=—The more commonly occurring starches are described by Richardson as they appear under the microscope magnified about 350 diameters.[168]

The illustrations, with the exception of the cassava starch, and the maize starch accompanying it were drawn by the late Dr. Geo. Marx from photographs made by Richardson in this laboratory. The two samples excepted were photographed for the author by Dr. G. L. Spencer.

_Maranta Starch._—Of the same type as the potato starch are the various arrowroots, the only one of which commonly met with in this country being the Bermuda, the starch of the rhizome of _Maranta arundinacea_, and the starch of turmeric.

The granules are usually not so varied in size or shape as those of the potato, averaging about 0.07 millimeter in length as may be seen in Fig. 48. They are about the same size as the average of the potato, but are not often found with the same maximum or minimum magnitude, which circumstance, together with the fact that the end at which the nucleus appears is broader in the maranta and more pointed in the potato, enables one to distinguish the two starches without difficulty. With polarized light the results are similar to those seen with potato starch, and this is a ready means of distinguishing the two varieties, by displaying in a striking way the form of the granule and position of the hilum.

_Potato Starch._—The starch grains of the potato are very variable in size, being found from 0.05 to 0.10 millimeter in length, and in shape from oval and allied forms to irregular and even round in the smallest. These variations are illustrated in Fig. 49, but the frequency of the smaller granules is not as evident as in some other cases. The layers are visible in some granules with great distinctness and in others hardly at all, being rather more prominent in the starch as obtained from a freshly cut surface. The rings are more distinct, too, near the hilum or nucleus, which in this, as in all tuberous starches, is eccentric, shading off toward the broader or more expanded portion of the granule. The hilum appears as a shadowy depression, and with polarized light its position is well marked by the junction of the arms of the cross. With polarized light and a selenite plate a beautiful play of colors is obtained. The smaller granules, which are nearly round, may readily be confused with other starches, but their presence serves at once to distinguish this from maranta or Bermuda arrowroot starch. Rarely compound granules are found composed of two or three single ones each with its own nucleus.

_Ginger Starch._—This starch is of the same class as those from the potato and maranta and several others which are of underground origin. In outline the granules are not oval like those named, but more rectangular, having more obtuse angles in the larger ones and being cylindrical or circular in outline in the smaller, as indicated in Fig. 50. They average nearly the same size as maranta starch, but are much more variable, both in size and form. The rings are scarcely visible even with the most favorable illuminations.

_Sago Starch._—This exists in two modifications in the market; as raw and as prepared sago. In the prepared condition it is characterized by a larger circular depression in the center of most of the granules. The rings are not visible. They are mostly circular in form or approaching it, and vary from 0.025 to 0.065 millimeter in diameter, as indicated in Fig. 51.

DRAWN BY GEO. MARX.

A. Hoen & Co., Lithocaustic]

DRAWN BY Geo. MARX.

A. Hoen & Co., Lithocaustic]

PLAIN ILLUMINATION.]

PLAIN ILLUMINATION.

A. Hoen & Co., Lithocaustic]

_Pea and Bean Starches._—These starches produce but a slight effect with polarized light. The rings are scarcely visible, and the hilum is stellate or much cracked along a median line, the bean more so than the pea, the latter resembling fresh dough kneaded again into the center as in making rolls, and the former the shape assumed by the same after baking. The grains of both are somewhat variable in size, ranging from 0.025 to 0.10 millimeter in length, as shown in Figs. 52 and 53.

_Wheat Starch_ grains are quite variable in size, varying from 0.05 to 0.010 millimeter in diameter. They belong to the same class as barley and rye, the hilum being invisible and the rings not prominent. The granules are circular disks in form, and there are now and then contorted depressions resembling those in pea starch. They are the least regular of the three starches named and do not polarize actively. The typical forms of these granules are shown in Fig. 54.

_Barley Starch_ is quite similar to that of wheat, but the grains do not vary so much in size, averaging 0.05 millimeter. They have rings which are much more distinct, and very small granules adhering to the largest in bud-like forms, as seen in Fig. 55.

_Rye Starch_ is more variable in size, many of the granules not exceeding 0.02 millimeter, while the largest reach 0.06 to 0.07 millimeter. It lacks distinctive characteristics entirely, and is the most simple in form of all the starches. Fig. 56 shows the appearance of the granules under the microscope.

_Oat Starch_ is unique, being composed of large compound masses of polyhedral granules from 0.12 to 0.02 millimeter in length, the single granules averaging 0.02 to 0.015 millimeter. It does not polarize actively, and displays neither rings nor hilum. The illustration, Fig. 57, shows its nature with accuracy.

_Indian Corn Starch._—The granules of maize starch are largely of the same size, from 0.02 to 0.03 millimeter in diameter, with now and then a few which are much smaller. They are mostly circular in shape or rather polyhedral, with rounded angles, as shown in Figs. 58 and 61. They form very brilliant objects with polarized light, but with ordinary illumination show but the faintest sign of rings and a well-developed hilum, at times star-shaped, and at others more like a circular depression.

_Rice Starch_ is very similar to that of maize, and is easily confused with it, the grains being about the same size. The grain, however, is distinguished from it by its polygonal form, and its well defined angles, as indicated in Fig. 59. The hilum is more prominent and more often stellate or linear. Several granules are at times united.

_Cassava Starch._—This variety of starch is obtained from the root of the sweet cassava, which grows in great profusion in Florida. It is compared with maize starch in Figs. 60 and 61. In the illustration the granules are represented as magnified 150 diameters. The grains of the cassava starch measure about 0.012 millimeter in diameter and resemble very nearly maize starch, except that they have greater evenness of outline.[169]

For further descriptions of starch grains the reader is referred to the work of Griffith, already cited.

These descriptions, it will be seen, do not agree entirely with those of some other authors, but they are based on a somewhat extensive experience.

There are peculiarities of size, shape and appearance of starch granules, which must be allowed for, and the necessity for every investigator to compare a starch which he is desirous of identifying with authentic specimens, must always be recognized.

AUTHORITIES CITED IN PART SECOND.

[23] Vines, Vegetable Physiology.

[24] Berichte der deutschen chemischen Gesellschaft, Band 23, S. 2136; Stone, Agricultural Science Vol. 6, p. 180. Page 59, eighth line from bottom insert “original” before “optical.” Page 60, second line from top, read _d_ instead of _l_ fructose.

[25] Herles, Zeitschrift des Vereins für die Rübenzucker-Industrie, 1890. S. 217.

[26] Tucker; Wiechmann; Sidersky; von Lippman; Tollens and Spencer.

[27] Bulletin No. 28, Department of Agriculture, Division of Chemistry, p. 197.

[28] Physikalisch-Chemische Tabellen, S. 42.

[29] Tucker’s Manual of Sugar Analysis, pp. 100 et seq.

[30] Vid. op. cit. supra, p. 108.

[31] Op. cit. supra, p. 109.

[32] Op. cit. supra, p. 110.

[33] Op. cit. supra, p. 114.

[34] Spencer’s Handbook for Sugar Manufacturers, p. 92.

[35] Landolt’s Handbook of the Polariscope, pp. 95 et seq.

[36] Robb, vid. op. cit. supra, p. 8.

[37] Spencer’s Handbook for Sugar Manufacturers, pp. 22 et seq. Tucker’s Manual of Sugar Analysis, pp. 120 et seq.

[38] Sidersky; Traité d’Analyse des Matières Sucrées, p. 104.

[39] Journal of the American Chemical Society, 1893. Vol. 15, p. 121.

[40] Comptes rendus, 1879. Seance du 20th Octobre 1879; Dingler’s polytechniches Journal, Band 223, S. 608.

[41] Landolt’s Handbook of the Polariscope. p. 120.

[42] Sidersky; Traité d’Analyse des Matières Sucrées, p. 97.

[43] Manual of Sugar Analysis, pp. 143 et seq.

[44] Landolt und Börnstein, Physikalisch-Chemische Tabellen. S. 460.

[45] Bulletin No. 31. Department of Agriculture, Division of Chemistry, p. 232.

[46] Zeitschrift des Vereins für die Rübenzucker-Industrie. 1870, S. 223.

[47] Tucker’s Manual of Sugar Analysis, p. 164.

[48] (bis). Gerlach, Spencer’s Handbook for Sugar Manufacturers, p. 91.

[49] Vid. op. cit. supra, p. 45.

[50] Vid. loc. et op. cit. supra.

[51] Gill; Journal of the Chemical Society, Vol. 24, 1871, p. 91.

[52] Wiley; American Chemical Journal, Vol. 6, p. 289.

[53] Vid. op. cit. supra, p. 301.

[54] Zeitschrift des Vereins für die Rübenzucker-Industrie, 1890. S. 876.

[55] Weber and McPherson; Journal of the American Chemical Society. Vol. 17, p. 320; Bulletin No. 43. Department of Agriculture, Division of Chemistry, p. 126.

[56] Zeitschrift des Vereins für die Rübenzucker-Industrie, 1888, S. 51.

[57] Vid. op. cit. supra, Ss, 699 und 763; 1890. S. 217.

[58] Bulletin de l’Association des Chimistes de Sucrerie et de Distillerie, May, 1890, p. 431.

[59] Neue Zeitschrift für Rübenzucker-Industrie, Band 19, S. 71.

[60] Journal of the Chemical Society, Transactions, Vol. 57, pp. 834, et seq.

[61] Op. cit. supra, p. 866.

[62] Op. cit. supra, 1891, p. 46.

[63] Neue Zeitschrift für Rübenzucker-Industrie, Band 19, S. 71.

[64] From γῦρος and δῦνᾶτός (δύνᾶμις).

[65] Landolt’s Handbook of the Polariscope, p. 125.

[66] Vid. op. cit. supra, pp. 48 et seq.

[67] Berichte der deutschen chemischen Gesellschaft, 1877, S. 1403.

[68] Die landwirtschaftlichen Versuchs-Stationen, Band 40, S. 307.

[69] Spencer’s Handbook for Sugar Manufacturers, p. 80; Landolt’s Handbook of the Polariscope, p. 216; Tollens’ Handbuch der Kohlenhydrate.

[70] Annalen der Chemie and Pharmacie, May, 1870.

[71] Tucker’s Manual of Sugar Analysis, p. 208.

[72] Rapport fait a la Société d’Encouragement d’Agriculture; Journal de Pharmacie et de Chimie, 1844. 3d serie, Tome 6, p. 301.

[73] Annalen der Chemie und Pharmacie, Band 39, S. 361.

[74] Jahrbücher für praktische Heilkunde, 1845, S. 509.

[75] Archives für Physiologische Heilkunde, 1848, Band 7, S 64.

[76] Rodewald and Tollens; Berichte der deutschen chemischen Gesellschaft, Band 11, S. 2076.

[77] Chemical News, Vol. 39, p. 77.

[78] The Analyst, Vol. 19, p. 181.

[79] Gaud; Bulletin de l’Association des Chimistes de Sucrerie et de Distillerie, Apr. 1895, p. 629; Comptes rendus, 1894, Tome 119, p. 604.

[80] Annalen der Chemie und Pharmacie, B. 72, S. 106.

[81] Journal of Analytical and Applied Chemistry, Vol. 4, p. 370.

[82] Wiley; Bulletin de l’Association des Chimistes de Sucrerie et de Distillerie, April, 1884.

[83] Vid. op. cit. supra, 1895, p. 642; Comptes rendus, Tome 119, 1894, p. 650.

[84] Annual Report, United States Department of Agriculture, 1879, p. 65; Zeitschrift für Analytische Chemie, Band 12, S. 296; Mohr Titrirmethode, sechste auflage, S. 508.

[85] Comptes rendus, 1894, Tome 119, p. 478.

[86] Gazetta Chimica Italiana, Tome 6, p. 322.

[87] Sidersky; Traité d’Analyse des Matières Sucrées, p. 148.

[88] Vid. op. cit. supra, p. 149.

[89] Neue Zeitschrift für die Rübenzucker-Industrie, Band 22, S. 220.

[90] Zeitschrift des Vereins für Rübenzucker-Industrie, 1889, S. 933.

[91] Vid. op. cit. supra, 1887, S. 147.

[92] Berichte der deutschen chemischen Gesellschaft, Band 23, No. 14, S. 3003; Zeitschrift des Vereins für die Rübenzucker-Industrie, 1891, S. 97.

[93] Ost; vid. op. et loc. cit. supra.

[94] Zeitschrift des Vereins für die Rübenzucker-Industrie, 1890, S. 187.

[95] Chemical News, Vol. 39, p. 77.

[96] The Analyst, 1894, p. 181.

[97] Chemical News, Vol. 71, p. 235.

[98] Journal de Pharmacie et de Chimie, 1894, Tome 30, p. 305.

[99] Pharmaceutical Journal, (3), 23, p. 208.

[100] Vid. op. cit. supra, (3), 25, p. 913.

[101] Sidersky; Bulletin de l’Association des Chimistes, Juillet, 1886 et Sept. 1888.

[102] Bodenbender and Scheller; Zeitschrift des Vereins für die Rübenzucker-Industrie, 1887, S. 138.

[103] Vid. op. cit. supra, 1889, S. 935.

[104] Ewell; Manuscript communication to author.

[105] Journal für praktische Chemie, 1880, Band 22, 46; Handbuch der Spiritusfabrication, 1890, S. 79; Zeitschrift des Vereins für die Rübenzucker-Industrie, 1879, S. 1050; _Ibid_, 1883, S. 769; _Ibid_, 1889, S. 734.

[106] Handbuch der Spiritusfabrication, 1890, 79.

[107] Wein; Tabellen zur quantitativen Bestimmung der Zuckerarten, S. 13. (The caption for the table on page 159 should read as on page 160.)

[108] Zeitschrift des Vereins für die Rübenzucker-Industrie, 1889, S. 735.

[109] Bulletin No. 43, Department of Agriculture, Division of Chemistry, p. 209.

[110] Chemiker-Zeitung, 1893, S. 548.

[111] Wein; Tabellen zur quantitativen Bestimmung der Zuckerarten, S. 35.

[112] Berichte der deutschen chemischen Gesellschaft, Band 16, S. 661.

[113] Vid. op. cit. supra, Band 22, S. 87.

[114] Chemisches Centralblatt, 1895, Band 2, S. 66.

[115] Comptes rendus; Tome 112, No. 15, p. 799.

[116] Vid. op. cit. supra, Tome 94, p. 1517.

[117] Journal of the Chemical Society, June, 1888, p. 610. (In the formulas for lactose and arabinose read H₂₂ and H₁₀ respectively.)

[118] American Chemical Journal, Vol. 11, No. 7, p. 469.

[119] Chemisches Centralblatt, 1889, No. 7.

[120] American Chemical Journal, Vol. 17, No. 7, pp. 507, 517.

[121] Comptes rendus, Tome 118, p. 426.

[122] Justus Liebig’s Annalen der Chemie, 1890. Band 257, S. 160.

[123] Journal of Analytical and Applied Chemistry, Vol. 7, pp. 68 et seq.

[124] Flint and Tollens; Berichte der deutschen chemischen Gesellschaft, Band 25, S. 2912.

[125] Vid. op. cit. supra, Band 23, S. 1751. (Read Günther.)

[126] Journal of Analytical and Applied Chemistry, Vol. 5, p. 421.

[127] Vid. op. cit. supra, p. 426.

[128] Berichte der deutschen chemischen Gesellschaft, Band 24, S. 3575.

[129] Journal of Analytical and Applied Chemistry, Vol. 7, p. 74.

[130] Chemiker-Zeitung, Band 17, 1743.

[131] Vid. op. cit. supra, Band 18, N. 51, S. 966.

[132] Monatshefte für Chemie, Band 16, S. 283; Berichte der deutschen chemischen Gesellschaft, Referate Band 28, S. 629.

[133] Papasogli; Bulletin de l’Association des Chimistes de Sucrerie et de Distillerie, Juillet 1895, p. 68.

[134] Gans und Tollens; Zeitschrift des Vereins für die Rübenzucker-Industrie, Band 38, S. 1126.

[135] Berichte der deutschen chemischen Gesellschaft, 20, S. 181; Zeitschrift des Vereins für die Rübenzucker-Industrie, 1891, S. 895.

[136] Zeitschrift des Vereins für die Rübenzucker-Industrie, 1891, S. 891.

[137] Chemiker-Zeitung, 1888, No. 2; Zeitschrift des Vereins für die Rübenzucker-Industrie, 1888, S. 347.

[138] Fischer; Berichte der deutschen chemischen Gesellschaft, Band 20, S. 821; Band 21, Ss. 988; 2631.

[139] Zeitschrift für physiologische Chemie, Band 11, S. 492.

[140] Vid. op. cit. supra, Band 12, No. 4, Ss. 355 et seq; No. 5, Ss. 377 et seq.

[141] Berichte der deutschen chemischen Gesellschaft, Band 20, S. 540.

[142] Sitzungsberichte der Mathematisch-Naturwissenschaften in Wien, Band 93, Heft 2, S. 912.

[143] Tollens; Handbuch der Kohlenhydrate; von Lippmann, Chemie der Zuckerarten.

[144] Wilder Quarter-Century Book, 1893; Abdruck aus dem Centralblatt für Bakteriologie und Parasitenkunde, Band 18, 1895, No. 1; American Journal of Medical Sciences, Sept., 1895.

[145] Griffiths, Principal Starches used as Food; Nägeli’s Beiträge zur näheren Kenntniss der Stärkegruppe.

[146] Zeitschrift für Physiologische Chemie, Band 12, Ss. 75-78.

[147] Maercker; Handbuch der Spiritusfabrikation, 1890, S. 90.

[148] Chemiker-Zeitung, Band 19, S. 1501.

[149] Paragraphs =28-32=, this volume.

[150] Vol. 2, p. 204.

[151] Chemisches Centralblatt, 1877, Band 8, S. 732.

[152] Chemiker-Zeitung, Band 19, S. 1501.

[153] Vid. op. cit. supra, S. 1502; Moniteur Scientifique, 1887, p. 538.

[154] Chemiker-Zeitung, Band 19, S. 1502.

[155] Vid. op. cit. supra, 1895, S. 1727.

[156] Chemiker-Zeitung, Band 19, S. 1502.

[157] Jahresberichte der Agrikulturchemie, 1892, S. 664.

[158] Journal de Pharmacie et de Chimie, 5ᵉ, Série, Tome 25, p. 394.

[159] Journal of the American Chemical Society, Vol. 17, p. 64.

[160] Repertorium der Analytischen Chemie, 1887, S. 299.

[161] Journal of the American Chemical Society, Vol. 16, p. 726.

[162] Förschungs Berichte über Lebensmittel, Hamburg; Abs., The Analyst, Vol. 20, p. 210.

[163] Rouvier; Comptes rendus, Tome 107, pp. 272, 278; Tome 111, pp. 64, 186; Tome 120, p. 1179.

[164] Bulletin 13, Department of Agriculture, Division of Chemistry, pp. 154 et. seq.

[165] Foods, Their Composition and Analysis, p. 139.

[166] Richardson, Vid. op. cit. 142, p. 158.

[167] Principal Starches used as Food, Cirencester, Baily & Son, Market Place.

[168] Vid. op. cit. 142, pp. 158 et seq.

[169] Bulletin 44, Department of Agriculture, Division of Chemistry, p. 14.

PART THIRD.

PROCESSES FOR DETECTING AND DETERMINING SUGARS AND STARCHES AND OTHER CARBOHYDRATES IN CRUDE OR MANUFACTURED AGRICULTURAL PRODUCTS.

=203. Introduction.=—In the preceding part directions have been given for the estimation of sugars and starches in approximately pure forms. In the present part will be described the most approved methods of separating these bodies and other carbohydrates from crude agricultural products and for their chemical examination. In many respects the processes which in a small way are used for preparing samples for analysis are employed on a large scale for technical and manufacturing purposes. It is evident, however, that the following paragraphs must be confined strictly to the analytical side of the question inasmuch as anything more than mere references to technical processes would lead into wide digressions.

In the case of sugars the analyst is for the most part quite as much in need of reliable methods of extraction and preparation as of processes for analysis. With starches the matter is more simple and the chief methods of separating them for examination were necessarily described in the previous part.

Sugars in fresh plants exist almost entirely in solution. This is true of all the great sources of the sugar of commerce, _viz._, the palm, the maple, the sugar beet and sugar cane. This statement is also true of fruits and the natural nectar of flowers. By natural or artificial drying the sugar may be reduced to the solid or semisolid state as in the cases of raisins and honey. In certain seeds, deficient in water, sugars may possibly exist in a solid state naturally, as may be the case with sucrose in the peanut and raffinose in cotton seed.

Starches on the other hand when soluble, are probably not true starches, but they partake more or less of a dextrinoid nature. Fine starch particles occur abundantly in the juices of some plants, as for instance sorghum, where they are associated with sugar and can be obtained from the expressed juice by subsidence. But even in such a case it is not certain that the starch enters into the general circulation. It is more likely formed locally by biochemical condensation of its constituents. Starches in a soluble or semisoluble state are transported, as a rule, to the tubers or seeds of plants where they are accumulated in large quantities as a reserve food for future growth. For a study of the plant metabolism whereby starch is produced and for its histological and physiological properties the reader may consult the standard authorities on vegetable physiology.[170]

=204. Sugar in the Sap of Trees.=—Many trees at certain seasons of the year, carry large quantities of sugar in their sap. Among these the maple and sugar palm are preeminent. The sap is secured by cutting a pocket into the side of the tree or by boring into it and allowing the sap to run into an appropriate receptacle through a spile. The content of sugar in the sap of the maple and palm varies greatly. In some cases it falls as low as one and a half and in others rises to as much as six or seven per cent.[171] In most cases the sugar in the maple sap is pure sucrose, but towards the end of the flowing season it may undergo changes of a viscous nature due to fermentation, or inversion, forming traces of invert sugar. In this country the sap of the maple may flow freely on any warm day in winter, but the sugar season proper begins about February 15th in Southern Ohio and Indiana, and about March 25th in Vermont. It lasts from six weeks to two months. The sap flows best during moderately warm, still days, after a light freeze.

In addition to sugar the maple sap contains a trace of albuminoid matters and some malic acid combined with lime. As a rule it can be subjected to polarization without preliminary clarification.

=205. Determination of Sugar in Saps.=—In most cases the sap may be directly polarized in a 200 millimeter tube. Its specific gravity is obtained by a spindle or pyknometer, and the percentage of sugars taken directly from the table on page 73, the degree brix corresponding to the sugar percentage.

On polarizing, the sugar percentage is calculated as follows:

Multiply the specific gravity of the sap by 100 and divide the product by 26.048. Divide the direct reading of the sap on the sugar scale by the quotient obtained above, and the quotient thus obtained will be the correct percentage of sugar in the original solution.

The formula is applicable for those instruments in which 26.048 grams represent the normal quantity of sugar which in 100 cubic centimeters reads 100 divisions on the scale. When other factors are used they should be substituted for 26.048 in the above formula.

The principle of the calculation is based on the weight of the sap which is contained in 100 cubic centimeters, and this is evidently obtained by multiplying 100 by the specific gravity of the sap. Since 26.048 is the normal quantity of sugar in that volume of the solution the quotient of the actual weight divided by that factor shows how many times too great the observed polarization is. The simple division of the polariscope reading by this factor gives the correct reading.

_Example_: Let the specific gravity of the sap be 1.015 and the observed polarization be 15.0. Then the true percentage of sugar in the sap is found by the equation:

101.5 : 26.048 = 15.0 : _x_.

Whence _x_ = 3.85 = percentage of sugar in the sap.

The process outlined above is not applicable when a clarifying reagent such as lead subacetate or alumina cream must be used. But even in these cases it will not be found necessary to weigh the sap. A sugar flask graduated at 100 and 110 cubic centimeters is used and filled to the first mark with the sap, the specific gravity of which is known. The clarifying reagent is added, the volume completed to the second mark with water, and the contents of the flask well shaken and thrown on a dry filter. The observation tube, which should be 220 millimeters in length, is then filled with the clear filtrate and the rest of the process is as described above. A 200 millimeter tube may also be used in this case and the observed reading increased by one-tenth.

=206. Estimation of Sugar in the Sap of Sugar Cane and Sorghum.=—In bodies like sugar cane and sorghum the sap containing the sugar will not flow as in the cases of the maple and sugar palm. The simplest way of securing the sap of the bodies named is to subject them to pressure between rolls. A convenient method of obtaining the sap or juice is by passing the cane through a small three-roll mill indicated in the figure. Small mills of this kind have been used in this division for many years and with entire satisfaction. Small canes, such as sorghum, may be milled one at a time, or even two or three when they are very small. In the case of large canes, it is necessary that they be split and only half of them used at once. The mill should not be crowded by the feed in such a way as to endanger it or make it too difficult for the laborer to turn. From fifty to sixty per cent of the weight of a cane in juice may be obtained by passing it through one of these small mills. Experience has shown that there is a little difference between the juice as first expressed and the residual sap remaining in the bagasse, but the juice first expressed may be used for analysis for control purposes as a fair representative of all that the cane contains.

To determine the percentage of juice expressed, the canes may be weighed before passing through the mill and the juice collected. Its weight divided by the weight of the original cane will give the per cent of the juice expressed, calculated on the whole cane. Instead of weighing the juice the bagasse may also be collected and weighed; but on account of the rapidity with which it dries the operation should be accomplished without delay. The expressed juice is clarified with lead subacetate, filtered and polarized in the manner described in former paragraphs. Instead of weighing the juice, its specific gravity may be taken by an accurate spindle and the volume of it, equivalent to a given weight, measured from a sucrose pipette.[172]

A sucrose pipette for cane juice has a graduation on the upper part of the stem which enables the operator to deliver double the normal weight for the polariscope used, after having determined the density of the juice by means of a spindle. A graduation of from 5° to 25° of the brix spindle will be sufficient for all variations in the density of the juice, or one covering a range of from 10° to 20° will suffice for most instances. The greater the density of the juice the less volume of it will be required for the weight mentioned. For general use, the sucrose pipette is graduated on the stem to deliver from forty-eight to 50.5 cubic centimeters, the graduations being in terms of the brix spindle. The graduation of the stem of this instrument is shown in the accompanying figure. In the use of the pipette it is only necessary to fill it to the degree on the stem corresponding to the degree brix found in the preliminary trial.

The quantities of juice corresponding to each degree and fractional degree of the brix spindle are given in the following table; calculated for the normal weight 26.048 grams for the ventzke and for 16.19 grams for the laurent scale. The measured quantities of juice are placed in a 100 cubic centimeter sugar flask, treated with the proper quantity of lead subacetate, the volume completed to the mark, and the juice filtered and polarized in a 200 millimeter tube. The reading of the polariscope is divided by two for the factor 26.048 and by three for the factor 16.19.

TABLE FOR USE OF SUCROSE PIPETTES.

Cubic centimeters Cubic centimeters
of juice for 26.048 of juice for 16.19
Degrees factor. Divide Degrees factor. Divide
brix. reading by two. brix. reading by three.

5.0 51.1 5.0 47.6
5.4 51.0 5.7 47.5
5.7 50.9 6.3 47.4
6.4 50.8 6.8 47.3
6.9 50.7 7.3 47.2
7.4 50.6 7.8 47.1
7.9 50.5 8.3 47.0
8.4 50.4 8.9 46.9
8.9 50.3 9.5 46.8
9.4 50.2 10.0 46.7
9.9 50.1 10.5 46.6
10.4 50.0 11.0 46.5
10.9 49.9 11.6 46.4
11.4 49.8 12.1 46.3
11.9 49.7 12.7 46.2
12.4 49.6 13.3 46.1
12.9 49.5 13.8 46.0
13.4 49.4 14.3 45.9
13.9 49.3 14.8 45.8
14.4 49.2 15.3 45.7
14.9 49.1 15.9 45.6
15.4 49.0 16.4 45.5
15.9 48.9 17.0 45.4
16.4 48.8 17.5 45.3
16.9 48.7 18.0 45.2
17.4 48.6 18.6 45.1
17.9 48.5 19.1 45.0
18.4 48.4 19.7 44.9
18.9 48.3 20.2 44.8
19.4 48.2
19.9 48.1

In ordering sucrose pipettes the factor for which they are to be graduated should be stated.

It is evident also that with the help of the foregoing table the measurements may be made by means of a burette. For instance, if the degree brix is found to be 19.9, 48.1 cubic centimeters are to be used. This quantity can be easily run from a burette. In order to make the pipette more convenient it has been customary in this laboratory, as practiced by Carr, to attach a glass tube with a stopcock by means of a rubber tube to the upper part of the pipette, whereby the exact level of the juice in the stem of the pipette can be easily set at any required mark.

In the polarization of dilute solutions, such as are found in the saps and juices referred to above, it must not be forgotten that the gyrodynat of the sucrose is increased as the density of the solution is diminished. This change introduces a slight error into the work which is of no consequence from a technical point of view, but becomes a matter which must be considered in exact determinations. To avoid the annoyance of calculating the gyrodynat for every degree of concentration, tables have been constructed by Schmitz and Crampton by means of which the actual percentage of sugar, corresponding to any degree of polarization, is determined by inspection. These tables may be used when extremely accurate work is required.[173]

=207. Measuring Sugar Juices with a Gravimeter.=—A convenient method of weighing sugar juices is the gravimetric process designed by Gird.[174] The apparatus is fully illustrated by Fig. 64. The hydrometer F has a weight of 26.048 grams and its stem is also graduated in degrees brix. The juice is poured into the cylinder A and allowed to stand until air bubbles have escaped. In filling A the finger is held over the orifice G so that the siphon tube B is completely filled, the air escaping at the vent C. After the tube is filled the finger is withdrawn from G and all the liquid which will run out at G allowed to escape. The sugar flask D is now brought under G and the hydrometer F allowed to descend into A. The hydrometer will displace exactly its own weight of liquid. For convenience of reading, the index E may be used which is set five degrees above the surface of the liquid in A. The number of degrees brix read by E is then diminished by five. The hydrometer has been improved since the description given by the addition of a thermometer which, in addition to carrying a graduation in degrees, also shows the correction to be made upon the degree brix for each degree read. It is evident that the hydrometer may be made of any weight, and thus the delivery of any desired amount of juice be secured.

=208. Determination of Reducing Bodies in Cane Juices.=—Sucrose in cane juices is constantly accompanied with reducing sugars, or other bodies which have a similar action on fehling liquor, which interfere to a considerable degree with the practical manufacture of sugar. It is important to determine with a moderate degree of accuracy the quantity of these bodies. These sugars or reducing bodies are of a peculiar nature. The author pointed out many years ago that these reducing bodies were without action on polarized light, and for this reason proposed the name anoptose as one characteristic of their nature.[175] It is also found that these bodies do not yield theoretically the quantity of alcohol which a true sugar of the hexose type would give.[176] It is entirely probable, therefore, that they are quite different in their nature from many of the commonly known sugars. On account of the difficulty of separating these bodies in a pure state their actual copper reducing power is not known. For practical purposes, however, it is assumed to be the same as that of dextrose or invert sugar and the percentage of these bodies present is calculated on that assumption. In the determination of these sugars or reducing bodies, the quantity weighed may be determined by an apparatus entirely similar to the sucrose pipette just described above. The quantity of juice used should be diluted as a rule to such a degree as not to contain more than one per cent of the reducing bodies. For the best work, the juices should be clarified with lead subacetate and the excess of lead removed with sodium carbonate. For technical control work in sugar factories, this process may be omitted as in such cases rapidity of work is a matter of considerable importance and the approximate estimation of the total quantity of reducing bodies is all that is desired.

For volumetric work, the solution of copper and the method of manipulation described in paragraph =117= are most conveniently used.

=209. Preservation of Sugar Juices for Analysis.=—Lead subacetate not only clarifies the juices of canes and thus permits of their more exact analytical examination, but also exercises preservative effects which enable it to be used as a preserving agent and thus greatly diminish the amount of work necessary in the technical control of a sugar factory. Instead, therefore, of the analyst being compelled to make an examination of every sample of the juice, aliquot portions representing the different quantities can be preserved and one analysis made for all. This method has been thoroughly investigated by Edson, who also finds that the errors, which may be introduced by the use of the lead subacetate in the analytical work, may be entirely avoided by using the normal lead acetate.[177]

In the use of the normal lead acetate, much less acetic acid is required in the polariscopic work than when the subacetate is used. The normal lead acetate is not so good a clarifying agent as the subacetate, but its efficiency in this respect is increased by the addition of a little acetic acid. In its use, it is not necessary to remove the lead, even for the determination of the reducing bodies.

For further details in regard to the technical determination of reducing bodies, special works may be consulted.[178]

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Principles and practice of agricultural analysis. Volume 3 (of 3), Agricultural productsChapter IX: Preface: To Volume Third (9)

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