ash of edible fruits often contains notable quantities of silica and sometimes considerable quantities of sand, added accidentally or by the collection of dust. The ash of fruit also quite universally contains iron. In some cases the quantity of iron amounts to as much as four percent of the total weight of the ash. The data in the above table are calculated on the percentage of total ash and not on the percentage of pure ash, that is, ash deprived of its carbon, sand, and carbonic acid.
There are some peculiarities in the composition of the ash of tropical fruits to which attention may be called. The citrus fruits contain somewhat larger amounts of lime and iron than ordinary fruits. The ash of the tamarind contains large quantities of silica. The ash of the banana has a low content of lime and magnesia and a high content of chlorin. Attention is also called to the fact that in the ordinary combustion of an organic substance to secure the mineral matter notable quantities of the phosphoric acid and chlorin contained may be lost. Therefore, the data for phosphoric acid and for chlorin are probably lower than would be the case if all of these substances present in the fruit had been secured in the ash. The ash of pineapples is not peculiar in any respect, nor does it contain any marked amount of a constituent by which it can be identified. The pineapple, as is seen, contains slightly more potash than the other tropical fruits.
Sugar and Acid in Fruit.
The palatable quality of fruit depends largely upon the aromatic substances which they contain in the form of essential oils, esters, and ethers, and especially upon their sugar and acid content. The sweet taste of sugar in fruits and also often in nuts is modified and relieved by the acid or astringent materials, chiefly tannin, with which it is associated. In the analyses indicating the composition of fruits and of nuts and also of vegetables the sugar has not always been given separately, but as one member of a group consisting of sugar, starch, and cellulose materials soluble in weak acid and alkalies, and for this reason deemed to be digestible. It seems advisable to supplement this information with a special table giving the average quantity of sugar and acid found in some of the principal fruits. It must not be forgotten that in individual cases the quantity of sugar and acid may vary largely from the average, but the following data may be regarded as expressing very accurately the average content of sugar and acid in the common fruits.
Sugar. Acid.
Percent. Percent.
Apples, Rhode Island Greening, 10.95 .70 as malic
" Winesap, 11.95 .50 " "
" Northern Spy, 11.80 .70 " "
Apricots, fresh, 11.01 1.15 " "
" dried, 29.59 2.52 " "
Bananas, 20.28 .30 " sulfuric
