Ingredients
- one centim of fehling's solution is measured into a graduated test
- 04 per cent
- one gram of flour is triturated
- 20 centims of mixture
- 16 centims of filtrate
- 9 per cent digitized by 23
Directions
(a) One centim of Fehling's solution is measured into a graduated test and gently boiled, the weak saccharine solution (i per cent.) is added drop by drop until the last trace of purple has disappeared. The points are, to keep the copper solution gently boiling throughout, and to bring critical observation to bear on the last trace of purple. Should the copper solution show signs of decomposition on boiling, before the addition of the saccharine solution, it is unfit for estimations. Too much yellow tijnt in the supernatant, after the experiment, means too much saccharine solution was added. The supernatant portion in the test tube should be as limpid as water. The constant dividend for a centim of Fehling's solution is half ('5), and the divisor is the centims required to decolourise, and the quotient is the percentage of glucose, e,gt Remember any dilution made and allow for same.
Centims decolourising. Glucose per cent.
It is clearly seen by this table that the small quantity of sugar contained in a filtrate obtained from a mixture of flour in water (one in ten or twenty), amounting in some cases to only '04 per cent, in a decimal mixture of flour and water, could scarcely be estimated by a centim of Fehling's solution. Hence for such weak solutions of saccharines, such as one in twenty flour fil- trates, the next quantitative test is of the greatest use and of great simplicity.
(b) A solution of glucose or maltose in water has no immediate reaction upon the cold subnorme of permanganate, but if lightly caramelised in a definite way by boiling one minute only from the commencement of boiling with one-tenth its volume of liquor potassae, i.e., solution of potash of the phar- macopoeia strength, the cooled caramelised solution reacts on the cold subnorme, and affords a most accurate quantitative test for glucose and maltose.
For Example. One gram of flour is triturated with a little water in a mortar for 2 minutes, and more water added to afford 20 centims of mixture. This mixture is poured upon a paper filter, and we shall obtain about 16 centims of filtrate. Suppose we find 8*8 centims decolourise the subnorme ='07 9 per cent
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