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]
- (A) = Per cent pure ash in fruit.
- (B) = Per cent manganomanganic oxid.
- (C) = Per cent phosphorus pentoxid.
- (D) = Per cent sulfur trioxid.
| Name. | (A) | Per cent potash. | Per cent soda. | Per cent lime. | Per cent magnesia. | Per cent ferric oxid. | (B) |
|---|---|---|---|---|---|---|---|
| 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. | (C) | (D) | Per cent silica. | Per cent chlorin. | |||
| 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]