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a temperature which at times may fall below the frost point on the surface
of the soil. The leaf of the potato, when it has once appeared above the sur-
face of the soil, is very susceptible to the action of frost. If killed at an early
stage it may grow again without replanting. The potato is a crop which
the farmer may plant early in the spring. There are other varieties which
are planted later, even in the middle of summer, and produce good results.
The planting season may continue over a period of two or three months.
During the growth of the crop by the cultivation of the soil the surface is
kept in good tilth, the weeds and grass prevented from growing, and the soil
gradually drawn up around the growing tubers with the hoe or plow in the
form of ridges. This heaping up of the soil tends to promote the develop-
ment of the tubers, affording them a loose and more abundant bedding and
a greater supply of plant food.

The greatest enemies to which the potato crop is obnoxious are found in
the various forms of the potato bug (Doryphora decemlineata), which feed upon
their leaves. To prevent the ravages of these insects it becomes necessary
to dust over the leaves of the growing plants some powerful insecticide which
will destroy the life of the insects feeding upon them. The active ingredient
of these insecticides is usually arsenic. Fortunately the growing tuber does
not absorb, so far as known, even traces of arsenic, or at least not more than
the merest trace, which may be used for insecticidal purposes. It is quite
impossible in most localities to secure a crop of potatoes without such treat-
ment. The alternative is a constant inspection of the growing plant and the
removal and killing of the bugs as they appear, but this is only practicable
over very small areas as its general application would increase the cost of
the product beyond the reach of the average consumer.

Yield.-Potatoes are produced in every state and territory of the United States. The statistics for the year ended December 31, 1905, show that the total area devoted to potatoes in the United States is 2,996,757 acres. The largest area in any one State is found in New York, namely, 428,986 acres, and the smallest area, aside from Arizona, not reported, is found in New Mexico, namely, 1,470 acres. The yield of potatoes for the year is given as 260,741,294 bushels. The largest total yield was in New York, the average yield per acre for the country being 87 bushels. The largest yield per acre is reported from Maine, namely, 175 bushels, and the smallest from Louisiana and Texas, namely, 64 bushels per acre. The average price per bushel for the whole country at the farm is 61.7 cents, making the total value of the crop $160,821,080. The highest price per bushel was obtained in Florida, namely, $1.20, and the lowest price per bushel in Nebraska, namely, 37 cents. The weight of a bushel of potatoes is 60 pounds. As the average amount of fermentable matter in potatoes grown in the United States is 20 percent,

POTATOES.

the total weight of fermentable matter in a bushel of potatoes is 12 pounds, which would yield approximately 6 pounds or 3.6 quarts of alcohol.

Composition.-Starch content: The quantity of starch in American grown potatoes varies from 15 to 20 percent. Probably 18 percent might be stated as the general average of the best grades of potatoes. In this connection it must be remembered that at the present time potatoes are grown in the United States chiefly for table use. Generally, only the imperfect or injured samples are used for stock feeding or for starch making, and this condition will probably continue as long as good edible potatoes bring a higher price for table use than can be obtained by utilizing them for starch or for feeding purposes.

Under the microscope the granules of potato starch have a distinctive appearance. They appear as egg-shaped bodies on which, especially the larger ones, various ring-like lines are seen. With a modified (polarized) light under certain conditions of observation a black cross is developed upon the granule. It is not difficult for an expert microscopist to distinguish -potato from other forms of starch by its appearance, which is well shown in Figs. 39 and 40. Many of the granules are quite large, and most of them are ovoid in shape.

The quantity of protein in the potato is quite low compared with that of cereal foods; in round numbers it may be said to be 2.5 percent. The potato contains very little material which is capable of fermentation aside from starch and sugars.

Sugar content: Although the potato is not sweet to the taste in a fresh state, it contains notable quantities of sugar. This sugar is lost whenever the potato is used for starch-making purposes, but is utilized when it is used for the manufacture of industrial alcohol. The percentage of sugar of all kinds in the potato rarely goes above 1 percent. The average quantity is probably not far from 0.35 percent, including sugar, reducing sugar, and dextrin, all of which are soluble in water. In the treatment of potatoes for starch making therefore it may be estimated that 0.35 percent of fermentable matter is lost in the wash water.

One German author, Saare, claims to have found much larger quantities of sugar in potatoes than those just mentioned. The minimum quantity found by this author is 0.4 percent, and the maximum 3.4 percent, giving a mean of 1.9 percent. Ten varieties of potatoes used for the manufacture of industrial alcohol were examined in the securing of these data. It appears that some varieties have a greater tendency to produce sugar than others. The German variety known as "Daber" contains the smallest quantities of sugar, while the variety known as "Juno" contains the largest quantities. The percentages of sugar, as reported by Saare, however, are larger than those reported by other observers, and probably are larger than are usually found. Average composition: Frazier, of the Cornell station, has collected analyses

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FIG. 39.-POTATO STARCH (X 200).-(Courtesy Bureau of Chemistry.)

291

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FIG. 40.-POTATO STARCH UNDER POLARIZED LIGHT (X 200).-(Courtesy Bureau of Chemistry.)

of a large number of different varieties of potatoes, and finds them to have the following average composition:

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White Elephant,

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Delaware,.

Do....

Do...

Do... Carmen,.

The following analyses show in detail the composition of potatoes from different localities:

VARIETY.

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Analysis of Maine potatoes: The Bureau of Chemistry a few years ago made an investigation in connection with the experiment station in Maine of the composition of potatoes grown in that state used for table purposes and for starch making. Some of the best varieties grown in different parts of the state were subjected to analysis, and the following results show them to be of quite uniform composition:

ANALYSES OF MAINE POTATOES.*

Average,

Water,....

Starch,..

Sugars and dextrins,.

WATER. STARCH. FIBER.

Cellulose,.

Protein,...

Ether extract,.
Ash,......

Undetermined,.

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75.00 percent

66

19.87

75.72 18.63 -55

.61

77.64 16.26
76.87
18.03 .66
76.57 17.07 .59

77.02

18.29

.66

2.19

2.31

2.25

2.12

-77

.08

2.25

2.06

1.81

.33

1.00

PROTEIN
NITROGEN ASH.
X6.25).

1.75

2.06

Percent. Percent.
2.12

2.06

2.19

2.31

2.56

2.06

2.38

2.16

*Maine Agr. Exp. Sta., Bul. 57, p. 147.

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1.44

.36

2.28

.06

1.26

.68

0.76 1.0604

.78

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79.41 percent

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14.51

"

Analysis of Vermont potatoes: Analyses made in Vermont and published in the report of the Vermont Experiment Station for 1901 show an average content of starch considerably less than that above given, namely:

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SPECIFIC
GRAVITY.

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1.0795

1.0867

1.0742

1.0803

1.1058

1.0921

1.0906

1.1129

1.0881

1.0852

1.0904

1.0745

1.1120

1.0967 1.0804

1.0881

293

Composition of Potatoes used in France for Industrial Purposes.-The following is regarded in France as an average composition of the potato suitable for industrial purposes:†

Water,..
Starch,...

Sugar, etc.,.
Cellulose,.
Protein,.

Fat,..

Ash,.

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POTATOES.

The total fermentable matter, as seen above, is a little over 19 percent, not allowing anything for the cellulose which is fermented. As a portion of the cellulose may also become a source of alcohol, it is observed that the average percentage of fermented matter in the French potato used for industrial purposes is not far from 20 percent.

The following varieties show a variation in starch content of 6.8 percent, the minimum being 15.9 and the maximum 22.7 percent:

CONSTITUENT.

Water,...
Protein,.
Fat,...

Starch and sugar,.
Crude cellulose,.
Ash,......

.71.00 percent

66

. 18.00

""

66

(6

66

KÖNIG.

Percent.

--75.48

1.06

1.65

2.12

1.95

.15 ..20.69

.II

1.60

.75 .98

"Encyclopédie Agricole," E. Saillard.

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Analysis of Potatoes from German Sources.-Average composition and starch content: The content of starch in potatoes examined in the laboratory of the Association of German Spirit Manufacturers during the year 1905 varied from 12.1 to 25.1 percent. Eleven percent of the total number examined contained between 12 and 14 percent of starch, 20 percent between 14 and 16 percent of starch, 13 percent between 16 and 18 percent of starch, 24 percent between 18 and 20 percent, 24 percent also between 20 and 22 percent, and 8 percent between 22 and 25.1 percent.

These data show that 56 percent of the total number of samples examined contained between 18 and 25 percent of starch. It is evident, therefore, that the general average content of starch in the potatoes used in the German distilleries is not far from 18 to 20 percent.

The mean composition of potatoes as given by three German authorities, namely, König, Lintner, and Wolff, is as follows:

AVERAGE ANALYSIS OF POTATOES BY THREE GERMAN AUTHORITIES.

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LINTNER.
Percent.

76.0

2.I

.2

19.7

.8

1.2

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WOLFF. Percent.

75.0

2.I
.2

20.7
I.I
.9

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