The organic constituents of plants and vegetable substances and their chemical analysis / by G.C. Wittstein ; authorised translation from the German original, enlarged with numerous additions, by Baron Ferd. von Mueller.

  • Georg Christian Wittstein
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: The organic constituents of plants and vegetable substances and their chemical analysis / by G.C. Wittstein ; authorised translation from the German original, enlarged with numerous additions, by Baron Ferd. von Mueller. Source: Wellcome Collection.

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    solvents, and is put into a glass-flask containing an equal weight of concentrated sulphuric acid, which is diluted with 50 times its weight of water; the contents of the flask are then heated to boil gently. From time to time a drop of the liquid is taken out with a glass-rod and put into a porcelain dish, adding a ■drop of solution of iodine. When neither a blue nor a violet or reddish colour is produced, the flask is left to cool, the acid liquid (containing the Starch as gi-ape-sugar) is filtered and washed until the acid reaction has disappeared; the liquid is mixed with the water used for washing; saturated (cold) with soda-ley, and its volume ascertained by cubic-centimeters. Now, measm-e from the blue alkaline solution of sulphate of <3opper, 10 cubic centimeters, pour them into a flask, holding iibout 100 cubic centimeters, add 40 cubic centimeters water, heat the mixtm^e to a gentle boiling heat, and add of the above neutralised solution of sugar gradually and in intervals, until every trace of blue has disappeared, and in its stead a yellowish tinge is observable. To find out the exact moment of the change of ■colour, place the flask on a piece of white pa]?er. This de- colouration of the cupric solution takes place after 0*05 grammes ■of grape-sugar, corresponding to 0*045 grammes of starch, have been added. It is easy herefrom to calculate the concentration of the liquid in question, and its previous amount of Starch. The quantity of Starch found in this way has to be added, if necessary, to that obtained before by kneading the substance. The sulphiiric acid, used for converting the Starch into grape- sugar, being very diluted, neither vegetable fibrin nor pectin which might be present, afiect by changes of theirs the calculation. Though, under all circumstances, the Starch is characterised with certainty and precision by its behaviour to iodine; there are dif- ferences of form and size, which to determine demands a micro- scope magnifying at least 400 diameters. Should it not be pos- sible to isolate the Starch, thin slices of the substance, wherein Starch has been indicated by iodine, are submitted to the micro- scopical examination. Stearic Acid = Csc H35 0 3 4- HO. Contained as tristearin in fats, especially solid ones. Saponify with soda-ley, decompose the soap with hydrochloric acid, dissolve the fat-acids in hot alcohol, allow to crystallise, press and recrystallise repeatedly, until the product fuses at 69-1° to 69-2°. Shea-bvitter is of all vegetable and animal fats the best adapted for preparing pure stearic acid, as it contains only the one solid fat-acid.—Forms pearly needles and leaflets, inodorous and tasteless, of perceptibly acid reaction, fuses at 69-1° to 69-2°, has at 9° to 11° a density of 1-000, boils and distils in a vacuum unaltered, is not soluble in water, dissolves in 40 parts cold absolute and in every proportion