395. Extraction with Water.—It is quite impossible to get an extract from fine-ground vegetable matter in pure water because the soluble salts of the sample pass at once into solution and then a pure water solvent becomes an extremely dilute saline solution. The aqueous extract may, however, be subjected to dialysis, whereby the saline matter is removed and the proteid matter, not precipitated during the dialytic process, may be regarded as that part of it in the original sample soluble in pure water. Nevertheless, in many instances, it is important to obtain an extract with cold water. In oatmeal the aqueous extract is obtained by Osborne as follows:[368] Five pounds of fine-ground meal are shaken occasionally with six liters of cold water for twenty-four hours, the liquid removed by filtration and pressure and the extraction continued with another equal portion of water in the manner noted. The two liquid extracts are united and saturated with commercial ammonium sulfate which precipitates all the dissolved proteid matter. The filtrate obtained is collected on a filter, washed with a saturated solution of ammonium sulfate and removed as completely as possible from the filter paper by means of a spatula. Any residual precipitate remaining on the paper is washed into the vessel containing the removed precipitate and the undissolved precipitate well beaten up in the liquid, which is placed in a dialyzer with a little thymol, to prevent fermentation, and subjected to dialysis for about two weeks. At the end of that time, the contents of the dialyzer are practically free of sulfates. The contents of the dialyzers are then thrown on a filter and in the filtrate are found those proteids first extracted with water, precipitated with ammonium sulfate and redissolved from this precipitated state by pure water. In the case of oatmeal, this proteid matter is not coagulated by heat, and may be obtained in the dry state by the evaporation of the filtrate last mentioned at a low temperature in vacuo. It is evident that the character of the proteid matter thus obtained will vary with the nature of the substance examined. In the case of oats, it appears to be a proteose and not an albumin.
396. Action of Water on Composition of Proteids.—When a body, such as oatmeal, containing many proteids of nearly related character, is exposed to the action of a large excess of water, the proteid bodies may undergo important changes whereby their relations to solvents are changed. After oatmeal has been extracted with water, as described above, the proteid matter originally soluble in dilute alcohol undergoes an alteration and assumes different properties. The same remark is applicable to the proteid body soluble in dilute potash. Nearly all the proteid matter of oatmeal is soluble in dilute potash, if this solvent be applied directly, but if the sample be previously treated with water or a ten per cent salt solution the subsequent proportion of proteid matter soluble in dilute potash is greatly diminished.[369] Water applied directly to the oatmeal apparently dissolves an acid albumin, a globulin or globulins, and a proteose. The bodies, however, soluble in water, exist only in small quantities in oatmeal. Experience has shown that in most instances, it is safer to begin the extraction of a cereal for proteid matter with a dilute salt solution rather than with water, and to determine the matters soluble in water alone by subsequent dialysis.
397. Extraction with Dilute Salt Solution.—In general, it is advisable to begin the work of separating vegetable proteids by extracting the sample with a dilute brine usually of ten per cent strength. As conducted by Osborne and Voorhees, on wheat flour, the manipulation is carried on as follows:[370]
The fine-ground whole wheat flour, about four kilograms, is shaken with twice that weight of a ten per cent sodium chlorid solution, strained through a sieve, to break up lumps, and allowed to settle for sixteen hours. At the end of this time, about half of the supernatant liquid is removed by a siphon or by decantation and filtered. Two liters more of the salt solution are added, the mixture well stirred and the whole brought onto the filter used above. The filtrate is collected in successive convenient portions and each portion, as soon as it is obtained, is saturated with ammonium sulfate. All the proteid matter is precipitated by this reagent. The precipitate is collected on a filter, redissolved in a convenient quantity of the salt solution and dialyzed for fourteen days or until all sulfates and chlorids are removed. The proteid matter, which is separated on dialysis, in this instance, is a globulin.
The proteid matter not precipitated on dialysis is assumed to be that part of the original substance soluble in water.
A part of the water soluble proteid matter obtained as above is coagulated by heat at from 50° to 80°. The part not separated by heat gives a precipitate on saturation with sodium chlorid.
In wheat there are found soluble in water two albumins and a proteose.[371]
In separating the albumin coagulating at a low boiling point from the dialyzed solution mentioned above, it is heated to 60° for an hour, the precipitate collected on a gooch, washed with hot water (60°), and then successively with ninety-five per cent alcohol, water-free alcohol and ether. On drying the residual voluminous matter on the filter over sulfuric acid, it becomes dense and horny, having in an ash free state, according to Osborne, the following composition:
| Per cent. | |
| Carbon | 53.06 |
| Hydrogen | 6.82 |
| Nitrogen | 17.01 |
| Sulfur | 1.30 |
| Oxygen | 21.81 |
398. Treatment without Precipitation with Ammonium Sulfate.—Where abundant means are at hand for dialyzing large volumes of solution, the preliminary treatment of the solution made with ten per cent sodium chlorid with ammonium sulfate may be omitted.