Lynne Wong's PhD thesis

examination of three portions of each filtrate. For the original contact solution, six average
values were recorded, three at the beginning and three at the end of the Brix determination.
All Brix values were corrected for instrument zero by using distilled water.
Figure 4.5. Use of glass rod with button-end to squeeze out solution.
If w 1 and w 3 are the mass of sample in the blank and test solution respectively, and w 2 is
the mass of distilled water in the blank, and w 4 the mass of the contact solution in the test
solution; p 1 and p 2 are the Brix of the sample blank before and after equilibration, and p 3
and p 4 are the Brix of the test solution before and after equilibration, the corrected blank
b = p 2 w 2 w 3 /(w 1 w 4 ), the net Brix increase p = p 4 – b, and the Brix-free water in the
sample = [100w 4 (1 – p 3 p -1 )]/w 3 .
(Note: A series of twelve samples could be determined in one batch.)
A number of precautions were taken:
- If a sample size smaller than 3 g was used, the mass of the contact solution and
distilled water was adjusted proportionately so as to keep the ratio of the contact
solution/sample at about 20.
- During the cooling process, the stopper was kept well pushed in to ensure that no air
entered the bottle before the introduction of the contact solution, since cellulose
fibres are avid absorbers of moisture; otherwise, the results will be under-estimated.
- Since stalk pith is fluffy and light, 3.5 g occupied a large volume in the bottle. To
ensure that it was well dried, it proved better to have the bottle lying down in the
oven rather than standing up, as there was more drying surface for the sample.
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