4 CIRCULAR 50, U. 8. DEPARTMENT OF AGRICULTURE 
water extract and calculated either as invert sugar or as dextrose. In 
a few cases, however, only the pressed juice was analyzed, and the data 
in such cases refer to sugar in this juice calculated as percentage of the 
original substance. Hither copper reduction or polarimetric methods 
were used, the former predominating. It was impossible to convert 
all of these figures to a strictly uniform basis, particularly where the 
reports did not give definite descriptions; but only minor differences 
are due to this irregularity. 
ACID 
Acid is the total free acid as determined by titration against stand- 
ard alkali. It is expressed as malic (M) or anhydrous citric (C) 
according to which was considered to predominate, and is calculated 
into percentage of the fresh substance. 
FUEL VALUE 
Fuel value is expressed in calories which were calculated on the 
basis of the physiological fuel values, or 4 calories per gram of protein 
and of carbohydrates and 9 per gram of fat. 
ACCURACY AND LIMITATIONS OF THE FIGURES 
The figures here presented are the result of a careful and critical 
study of the source material. They are as reliable and accurate as 
they could be made with the data available. There are, however, 
certain necessary limitations imposed on any such attempt to give a 
composite picture of substances that vary as much among themselves 
as do the individual fruits in any one group. ‘The figures should be 
used, therefore, with an understanding of their limitations. 
On account of this variability in the make-up of fruits the averages 
of a class can be only rough estimates at best of the composition 
of a particular sample. Some of the averages represent samples from 
numerous types of the fruit and from various localities and growing 
conditions, and these probably are fairly reliable as average figures for 
their class. But in the case of some others it was impossible to get 
data that could be regarded as representative of the class as a whole. 
Many of the data used in this study came from analyses that were 
incomplete in the sense that not all of the constituents that are in the 
table were determined. ‘This will be evident from the differences in 
the number of analyses as shown in the last line under each fruit. 
Attention should be called in this connection to the fact that the 
determinations of a particular constituent, as sugars for example, may 
have come from an entirely different lot of material than that on 
which water content was determined. This accounts for some of the 
discrepancies. 
In general, it would be expected if all of the analyses were complete 
that the sum of sugar, fiber, and acid would be less than the total 
carbohydrates and, since ripe fruits have little or no starch, would 
come within 1 to 3 per cent of it. But in some cases the total of these 
three substances is greater, and in others it does not come within 3 
per cent of it. Such differences may be due either to the errors of 
sampling or to inaccuracy in analytical technic. Possibly, however, 
there may be in some fruits undetermined substances in excess of 3 
per cent. 
