Chemical report on the mode of detecting vegetable substances mixed with coffee for the purpose of adulteration / by Professor Graham, Dr. Stenhouse and Dugald Campbell.

  • Graham Thomas, 1805-1869.
Date:
[1852]
Catalogue details

Licence: Public Domain Mark

Credit: Chemical report on the mode of detecting vegetable substances mixed with coffee for the purpose of adulteration / by Professor Graham, Dr. Stenhouse and Dugald Campbell. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    To these Kochleder had lately added citric acid (C,2H50,,+ 3HO), in the small proportion of 2 grains in a pound of coffee ; also a trace, too small to be estimated by weight, of viridic acid (Cj4Hg07). This last substance is the acid obtained by exposing solutions of the neutral and basic caifeates to the influence of the air. The green colour of raw coffee is believed by E-ochleder to be owing to a small quantity of viridate of lime. The evidence upon which Rochleder rests the existence of palmitic and citric acids in coffee does not appear to us quite decisive. The formulae given by that chemist for both caffeic and viridic acids are doubtful. It is also stated by Rochleder, that when dried caffeic acid is submitted to destructive distillation, a small quantity of crystals were obtained, which he considered to be pyrocatechine. The ex- periment repeated by us on a considerable scale gave a negative result. Kochleder finds caffeic acid in Paraguay tea (iZex Para- guayensis), as well as in coffee. This statement we must also doubt. The acid of the Paraguay tea has been examined by us, and found to have a certain resemblance to caffeic acid, but not to be identical with it. Free caffeic acid, when strongly heated in an open vessel, emits the peculiar odour of roasted coffee ; but the acid from Paraguay tea emits a perfectly different odour when similarly treated. The sugar of coffee may be inferred to exist in a peculiar con- dition, as was before hinted, from the fact that when the coffee is roasted, none of its sugar appears to be converted into grape- sugar, as it does not affect Trommer's test; while, when 7 grains of cane-sugar were added to 100 grains of coffee, and the whole roasted in the usual way, abundant indications of grape-sugar were obtained by the same test. M. Pay en gives the proportional quantities of the different substances which he finds in raw coffee as follows :— Cellular tissue 34-000 Hygroscopic water ..... 12*000 Fats . . . . . 10- to 13-000 Starch, sugar, dextrin, and vegetable acids 15-500 Legumin . I-000 Chlorogenate of potash and caffeine . . 3-500 Nitrogenous portion . . . • • 3-000 Free caffeine . . . . • • 0-800 Thick insoluble ethereal oil . . . O'OOl Aromatic oil . . . . • • 0-002 Mineral constituents: potash, lime, mag- nesia, phosphorus, sulphur, silica, and traces of chlorine . ... . 6-697