=575. Composition of Ash of Fruits.=—Two or three kilograms of the
dried sample are incinerated at a low temperature and burned to a white
ash in accordance with the directions given in paragraphs =28-32=.
The composition of the ash is determined by the methods already
described.[586]
The pure ash of some common whole fruits has the following
composition:[587]
Name. Per Per Per Per Per Per Per
cent cent cent cent cent cent cent
pure potash. soda. lime. magnesia. ferric mangano-
ash oxid. manganic
in oxid.
fruit.
Prune 0.47 63.83 2.65 4.66 5.47 2.72 0.39
Apricot 0.51 59.36 10.26 3.17 3.68 1.68 0.37
Orange 0.43 48.94 2.50 22.71 5.34 0.97 0.37
Lemon 0.53 48.26 1.76 29.87 4.40 0.43 0.28
Apple 1.44 35.68 26.09 4.08 8.75 1.40
Pear 1.97 54.69 8.52 7.98 5.22 1.04
Peach 4.90 27.95 0.23 8.81 17.66 0.55
------------------------------------------------------------
Name. Per Per Per Per
cent cent cent cent
phosphorus sulfur silica. chlorin.
pentoxid. trioxid.
Prune 14.08 2.68 3.07 0.34
Apricot 13.09 2.63 5.23 0.45
Orange 12.37 5.25 0.65 0.92
Lemon 11.09 2.84 0.66 0.39
Apple 13.59 6.09 4.32
Pear 15.20 5.69 1.49
Peach 43.63 0.37
=576. Dried Fruits.=—A method of preserving fruits largely practiced
consists in subjecting them, in thin slices or whole, to the action
of hot air until the greater part of the moisture is driven off. The
technique of the process is fully described in recent publications.[588]
It has been shown by Richards that fruit subjected to rapid evaporation
undergoes but little change aside from the loss of water.[589]
In the analyses of dried fruits the methods already described are used.
The presence of pectin renders the filtration of the aqueous extract
somewhat difficult, and in many cases it is advisable to determine the
sugars present in the extract without previous filtration.
=577. Zinc in Evaporated Fruits.=—Fruits are commonly evaporated on
trays made of galvanized iron. In these instances a portion of the zinc
is dissolved by the fruit acids, and will be found as zinc malate etc.,
in the finished product. The presence of zinc salts is objectionable
for hygienic reasons, and therefore the employment of galvanized trays
should be discontinued. The presence of zinc in evaporated fruits may
be detected by the following process.[590] The sample is placed in
a large platinum dish and heated slowly until dry and in incipient
combustion. The flame is removed and the combustion allowed to proceed,
the lamp being applied from time to time in case the burning ceases.
When the mass is burned out it will be found to consist of ash and
char, which are ground to a fine powder and extracted with hydrochloric
or nitric acid. The residual char is burned to a white ash at a low
temperature, the ash extracted with acid, the soluble portion added to
the first extract and the whole filtered. The iron in the filtrate is
oxidized by boiling with bromin water and the boiling continued until
the excess of bromin is removed. A drop of methyl orange is placed in
the liquid and ammonia added until it is only faintly acid. The iron is
precipitated by adding fifty cubic centimeters of a solution containing
250 grams of ammonium acetate in a liter and raising the temperature to
about 80°. The precipitate is separated by filtration and washed with
water at 80° until free of chlorids. The filtrate is saturated with
hydrogen sulfid, allowed to stand until the zinc sulfid settles and
poured on a close filter. It is often necessary to return the filtrate
several times before it becomes limpid. The collected precipitate is
washed with a saturated solution of hydrogen sulfid containing a little
acetic acid. The precipitate and filter are transferred to a crucible,
dried, ignited and the zinc weighed as oxid. Small quantities of zinc
salts added to fresh apples which were dried and treated as above
described, were recovered by this method without loss. Other methods of
estimating zinc in dried fruits are given in the bulletin cited.
Evaporated apples contain a mean content of 23.85 per cent of water and
0.931 per cent of ash.
The mean quantity of zinc oxid found in samples of apples dried in
the United States is ten milligrams for each 100 grams of the fruit,
an amount entirely too small to produce any toxic effects. When zinc
exists in the soil it will be found as a natural constituent in the
crop.[591]
=578. Composition of Watermelons and Muskmelons.=—In the examination of
melons a separation of the rind, seeds and meat is somewhat difficult
of accomplishment, since the line of demarcation is not distinct.
In watermelons the separation of rind and meat is made at the point
where the red color of the meat disappears. In muskmelons no such
definite point is found and in the examination of these they are taken
as a whole. The total moisture, ash and nitrogen may be determined
in the whole mass or in the separate portions. The sugars are most
conveniently determined in the expressed juices. The mean composition
of the melons given below is that obtained from analyses made in the
Department of Agriculture.[592]
COMPOSITION OF MELONS.
Total
Total weight, Juice, proteids, Ash,
grams. per cent. per cent. per cent.
-------------------------------------------------------------
Watermelons 10330 meat 83.99 6.12 0.37
rind 81.02
-------------------------------------------------------------
Muskmelons 3407 80.23 6.45 0.57
COMPOSITION OF JUICE.
Sucrose in Reducing sugars Ash in
juice, in juice, juice,
per cent. per cent. per cent.
-------------------------------------------------------------
Watermelons meat 1.92 meat 4.33 meat 0.31
rind 0.34 rind 2.47 rind 0.38
-------------------------------------------------------------
Muskmelons 1.02 3.04 0.53