Part 7

Under the proper headings the uses of these principal solvents will be described, but a complete discussion of their action, especially on samples of a vegetable origin, should be looked for in works on plant analysis.

The application of acids and alkalies for the extraction of carbohydrates, insoluble in water and alcohol, will be described, in the paragraphs devoted to the analysis of fodders and cereals. The extraction of these matters, made soluble by ferments, will be discussed in the pages devoted to starch and artificial digestion. It is thus seen that the general preliminary treatment of a sample preparatory to specific methods of examination is confined to drying, extraction with ether and alcohol, and incineration.

=43. Recovery of the Solvent.=—In using such solvents as ether, chloroform, and others of high value, it is desirable often to recover the solvent. Various forms of apparatus are employed for this purpose, arranged in such a way as both to secure the solvent and to leave the residue in an accessible condition, or in a form suited to weighing in quantitive work. When the extractions are made according to the improved method of Knorr, the flask containing the extract may be at once connected with the apparatus shown in figure 25. A represents the flask containing the solvent to be recovered, W the steam-bath, B the condenser sealed by mercury, M and R the flask receiving the products of condensation. It will be found economical to save ether, alcohol, and chloroform even when only a few cubic centimeters remain after the extraction is complete. In the figure the neck of the flask A is represented as narrower than it really is. The open end of the connecting tube, which is sealed on A by mercury, should be the same size as the tube connecting with the condenser in the extraction apparatus.

It often happens that materials which are dissolved by the ordinary solvents in use are to be collected in open dishes in order that their properties may be studied. At the same time large quantities of solvents must be used, and it is desirable to have some method of recovering them. The device shown in Fig. 26 has been found to work excellently well for this purpose. It consists of a steam-bath, W, and a bottle, B, with the bottom cut off, resting on an iron dish, P, containing a small quantity of mercury, enough to seal the bottom of the bottle. The dish containing the solvent is placed on the mercury, and the bottle placed down over it, forming a tight joint. On the application of steam the solvent escapes into the condenser, C, and is collected as a liquid in the flask A. In very volatile solvents the flask A may be surrounded with ice, or ice-cold water passed through the condenser. When an additional quantity of the solvent is to be added to the dish for the purpose of evaporating it is poured into the funnel F, and the stopcock H opened, which allows the material to run into the dish in B without removing the bottle. In this way many liters of the solvent may be evaporated in any one dish, and the total amount of extract obtained together. At the last the bottle B is removed, and the extract which is found in the dish is ready for further operations.

AUTHORITIES CITED IN PART FIRST.

Sidersky: Traité d’Analyse des Matières Sucrées, p. 311.

Die Agricultur-Chemische Versuchs-Station, Halle a/S., S. 34. (Read Dreef instead of Dree.)

Report of Commissioner of Fish and Fisheries, 1888, p. 686.

Vid. op. cit. 2, p. 14.

Journal of the American Chemical Society, Vol. 15, p. 83.

Chemical Division, U. S. Department of Agriculture, Bulletin No. 28, p. 101.

Not yet described in any publication. Presented at 12th annual meeting of the Association of Agricultural Chemists, Aug. 7th, 1895.

Vid. op. cit. 6, p. 100.

Cornell University Agricultural Experiment Station, Bulletin 12.

(bis. p. 28). Vid. op. cit. 2, p. 15.

Bulletin No. 13, Chemical Division, U. S. Department of Agriculture, Part First pp. 85-6.

Bulletin de 1’ Association des Chimistes de Sucrerie, 1893, p. 656.

Chemical News, Vol. 52, p. 280.

Presented to 12th Annual Convention of the Association of Official Agricultural Chemists, Sept. 7th, 1895.

Vid. Volume First, p. 411.

Vid. op. cit. 2, p. 17.

Dragendorff, Plant Analysis.

Vid. op. cit. 6, p. 96.

Journal of Analytical and Applied Chemistry, Vol. 7, p. 65, and Journal of the American Chemical Society, March 1893.

Vid. op. cit. 16.

Vid. op. cit. 6, p. 99.

Vid. op. cit. 6, p. 103.

PART SECOND.