T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y .
June, 1911
Table TV contains the analyses of pineapples when approximately one-fourth ripe. We note that there is a TABLEI V -THE COMPOSITIONOF PISEAPPLES ABOUT ONE-FOURTH RIPE U Sugars Polarization.
2
126 129 130 149 150
Av.
0.62 0 59 0.59 0.72 0.75
-
0 65
----
.-a
0'
_--_/ * _ _-
i
.3
-
i
h
$:
7.34 7.56 8.36 9.20 10.93
3.03 2.53 2.83 2.77 2.56
8.68
2.74
-
_
3.79 3.34 3.83 5.89 5.25
_
~
4.42
6.82 5.87 6.66 8.66 7.81
2 2 2 4 4
8 2 6
5 0
-2.0 -2.1 -2.3 -3.0 -2.7
32 28.4 29.4 30.8 30
7.16
slight increase in acidity and also a considerable increase in sucrose as compared with the green fruit. Table V shows the composition of pineapples when half ripe. When the fruit has attained this developTABLE\'.--THE
116 117 124 125
0.78 0.67 0.63 0.54
Av. 0 . 6 5
COMPOSITION OF PINEAPPLES HALFRIPE. sugars. Polarization.
11.83 10.36
... ...
2.74 2.61 2.38 4.16
7.33 6.70 6.83 6.09
10,07 9.31 9.21 10.25
...
2.97
6.74
9.71
5.7 5.0 4.9 5.0
-3.6 -3.5 -3.8 -2.7
31.8 31.7 30.5 32.2
ment fully three-quarters of its maximum sugar has been stored up. SUMMARY.
The composition of Hawaiian pineapples varies considerably. The total sugar content on the one hand was found to vary from 9.15 per cent. to 15.23 per cent., while on the other there is a range in acidity of from 0 . 2 2 per cent. to I . 16 per cent. Generally, though not always, the acidity increases with an increase in sugars. The average composition of pineapples grown in Hawaii is about equal t o that reported from other countries. Green pineapples contain less acidity than the ripe fruit and also a small percentage of fiber, reducing sugar and sucrose. Dextrin and starch do not occur in important quantities in pineapples a t any stage. The reducing sugars and sucrose stand in inverse ratio to that of the ripe fruit. I n the ripening of pineapples gathered green, the most important chemical change tha't takes place is the conversion of reducing sugars into sucrose, but the total sugar content appears not to be increased. The cells of green pineapples as seen under the highpower microscope contain. a thickened layer on the cell walls, which renders i t difficult to express the juice from the cells. I n the ripening process this layer gradually becomes dissolved away until a t maturity the cell walls are extremely thin and easily ruptured. With pineapples that are gathered green and allowed to ripen the thickened coat on the cell walls also becomes dissolved, thus apparently increas-
405
iing the juice in the fruit but without materially changing its concentration. During the normal ripening of the pineapple a rapid accumulation of sugars and a slight increase in acidity takes place. When the fruit becomes approximately half ripe, it contains a t least three-fourths of its maximum sugars. THE DETERMINATIONS OF TOTAL SOLIDS IN M1LK.O By PAULPOETSCHKE. Received Feb. 24, 1911.
I n the routine contamination of milk, the analysis is usually restricted to the determination of total solids, fat and specific gravity. Generally an examination for the more common preservatives is also included. The object of the present article is to consider particularly the determination of total solids as accomplished by the aid of a special pipette devised for delivering five grams of milk of known specific gravity. Inasmuch as the specific gravity is essential to the proper use of this pipette some essential features relating to specific gravity will be considered. Specific Gravity.-The New York Board of Health lactometer is the instrument usually employed in routine milk inspection. These instruments, as commonly constructed, require a comparatively large volume of milk, and if used for general laboratory work, would greatly inconvenience the inspector when many samples are taken for examination. Although many lactometers of reduced size are in use, it may be of interest to describe one of these forms,z which require but four ounces of milk. Fig. I is an exact representation of the instrument. A cylindrical jar (height I I . o cm., diameter 4 . 3 cm.), made of brass tubing with a copper bottom soldered thereto, serves as a container for the milk. A sufficient quantity of the well-mixed sample, cooled to a few degrees below 60' F., is poured into the jar and stirred with a dairy thermometer until the temperature reaches 60' F. The lactometer is then carefully lowered into the jar, and when it becomes stationary, the reading recorded. Too much stress cannot be laid upon a proper standardization of the instrument I have found lactometers to be incorrectly graduated in some cases to the extent of 4' to 5 ' . The simplest method of standardization is to compare the instrument in question with a standard lactometer. However, if such a standard is not a t hand, a series of salt solutions are prepared and their specific gravity determined a t 60' F. with a pycnometer, as in the following case, Table I : TABLEI. Specific gravity at 60' F . , b y pycnometer, 1 ,0245 1.0278 1.0312 1
2
Observed reading on instruments (Standard),
Corresponding lactometer. 84.5' 96 .O 107 .o
--One. Two.
7
84.0' 96.0 107.0
84.0' 96.0 107.0
Read before N. Y .Section Am. Chem. SOC..Feb. 10, 1911. Devised some years ago b y Dr. Deghute, of this laboratory.
T H E J O U R N A L OF I N D U S T R I A L A.Vn E.VGl.NEERII\'G
406
Having thus verified the standard, we can proceed to standardize other instruments by comparison, which is much simpler, since i t is not necessary t o standardize at 60' F. The comparison can be made a t any other temperature, ,as long as the temperature of the solution remains uniform while the instrument in question is compared with the standard. Table 11 gives the result of comparison of several instruments wit,h the standard: 'TA",.R
1.artonictri xiumber
3
rending 011
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ia
