In a coffee examined by Ewell the percentage of sucrose was found to be 6.34. The pentose yielding constituents of the coffee bean amount to from eight to ten per cent.
When coffee meal is extracted with a five per cent solution of sodium carbonate, a gummy substance is obtained, which is precipitable by alcohol. This gum, after washing with hydrochloric acid containing alcohol, gives a gray, translucent, hard mass on drying. On hydrolysis it yielded 75.2 per cent of dextrose, on distillation with hydrochloric acid, thirteen per cent of furfuraldehyd and, on oxidation with nitric acid, 18.7 per cent of mucic acid. This gum, therefore, consists chiefly of a mixture of galactan, xylan and araban.
585. Estimation of Galactan.—From three to five grams of the substance supposed to contain galactan are placed in a beaker with sixty cubic centimeters of nitric acid of 1.15 specific gravity. The mixture is evaporated on a steam bath until it is reduced to one-third of its original volume, allowed to stand for twenty-four hours, ten cubic centimeters of water added, well stirred and again allowed to stand for twenty-four hours, until the mucic acid is separated in a crystalline form. To remove impurities from the mucic acid it is separated by filtration, washed with not to exceed twenty cubic centimeters of water, placed together with the filter in the beaker, from twenty-five to thirty cubic centimeters of ammonium carbonate solution, containing one part of dry ammonium carbonate, nineteen parts of water and one part of ammonium hydroxid, added and heated to near the boiling point. The mucic acid is dissolved by the ammonium carbonate solution and any insoluble impurity separated by filtration, the filtrate being received in a platinum dish, the residue well washed and the entire filtrate and wash water evaporated to dryness on a steam bath acidified with dilute nitric, well stirred and allowed to stand until the mucic acid separates in a crystalline form. The separation is usually accomplished in half an hour, after which time the crystals of mucic acid are collected on a tared filter, or gooch, and washed with not to exceed fifteen cubic centimeters of water followed with sixty cubic centimeters of alcohol, then with ether, dried at 100° and weighed. For computing the amount of galactose, one gram of the mucic acid is equal to 1.333 of galactose and one gram of galactose is equal to nine-tenths gram of galactan. Before the commencement of the operation, the material should be freed of fatty matters in the case of oily seeds and other substances similar thereto.[603]
586. Revised Factors for Pentosans.—The factors given in paragraph [154] have lately been recalculated by Mann, Kruger and Tollens, and as a result of their investigations the following factors are now recommended.[604] The quantity of furfurol is derived from the weight of furfurolhydrazone obtained by the formula:
- 1. Furfurolhydrazone × 0.516 + 0.0104 = furfurol.
- 2. Furfurol × 1.84 = pentosans.
- 3. Furfurol × 1.64 = xylan.
- 4. Furfurol × 2.02 = araban.
The pentoses (xylose, arabinose) may be calculated from the pentosans (xylan, araban) by dividing by 0.88.
The method of procedure preferred for the estimation of the pentosans is that described in paragraph [157]. The phloroglucin is dissolved in hydrochloric acid of 1.06 specific gravity before it is added to the furfurol distillate. The latest factor for converting the phloroglucid obtained into furfurol is to divide by 1.82 for small quantities and 1.93 for large quantities. After the furfurol is obtained, the factors given above are applied.
587. Application of Roentgen Rays to Analysis.—The detection of mineral matters in vegetable substances by roentgen photography has been proposed by Ranvez.[605] This process will prove extremely valuable in detecting the lacing of teas with mineral substances. Practically, it has been applied by Ranvez in the detection of mineral substances mixed with saffron with fraudulent intent.
Barium sulfate is often mixed with saffron for the purpose of increasing its weight. Pure saffron and adulterated samples are enclosed in capsules of black paper and exposed on the same sensitive plate for a definite time to the rays emanating from a crookes tube. In this case the pure saffron forms only a very faint shadow in the developed negative, while the parts to which barium sulfate are attached produce strong shadows. The principle involved is applicable to a wide range of analytical research.