Albumin peptone, however, gives with the acid named in concentrated solution a precipitate easily soluble in an excess of the reagent. In the analysis of cow’s milk but not of human milk, this acid can be used for the estimation of the albuminoid substances. With both kinds of milk it can be used for the estimation of the albumin after the removal of the casein.
After precipitation of the albuminoid bodies, the milk sugar can be estimated by polarizing the filtrate and, volumetrically after removal of the excess of the acid by evaporation. By means of trichloracetic acid it is possible to separate albumin peptone from mucus and mucus peptone. A similar reaction is also produced by dichloracetic acid, but the reaction with this last agent is less delicate than with the other. Neither mucus nor albumin is precipitated by chloracetic acid.
380. Action of Albumins on Polarized Light.—Many of the albumins and albuminates, when in solution, strongly deflect the plane of polarized light to the left.[346]
The gyrodynats of some of the albumins and albuminates are given below:
| Serum albumin | [α]D = | -57°.3 to -64°.6. |
| Egg albumin | [α]D = | -35°.5 to -38°.1. |
| Serum globulin | [α]D = | -47°.8. |
| Milk albumin | [α]D = | -76°.0 to -91°.0. |
Our knowledge of the gyrodynatic numbers of the proteids and allied bodies is too fragmentary to be of any great help in analytical work. In practice, the rotatory power of these bodies becomes a disturbing force in the determination of milk sugar.[347] A further study of this property of certain proteids may lead to analytical processes for their detection and determination, but no reliable methods for this can now be recorded.
381. Alkaloidal Nitrogen.—Only a general statement can be made here in respect of the detection of alkaloidal nitrogen in vegetable or animal tissues. Alkaloids are not found in healthy animal tissues and the description of methods for isolating and detecting ptomaines is foreign to the purpose of this work. In vegetable tissues the presence of alkaloids may be established by the following methods of examination.
The fine-ground tissues are made to pass a sieve of half millimeter mesh and when suspended in water are acidified with sulfuric. The mixture is then thoroughly extracted by shaking in a separatory funnel with petroleum ether, benzene and chloroform, successively. Some resins, glucosids and a few alkaloidal bodies not important here are extracted by this treatment.
The residue is made distinctly alkaline with ammonia and treated as above with the same solvents. In the solution obtained as last mentioned nearly all the alkaloidal bodies found in plants are contained.
All the alkaloids in a plant may be obtained by digesting the finely divided material with dilute sulfuric acid. The acid solution thus obtained is made nearly neutral with ammonia or magnesia, concentrated to a sirup, and gums, mucilage, etc. thrown out by adding about three volumes of ninety-five per cent alcohol. The alkaloids are found in the filtrate. The alcohol is evaporated from the filtrate and the residue tested for alkaloids by group reagents.[348] Potassium mercuric iodid and phosphotungstic and molybdic acids are types of these reagents.