The hydrates of albumen have rotation powers which vary from [_a_]_{D} = -71°.40 to [_a_]_{D} = -79°-05. From the chaotic state of knowledge concerning the specific rotating power of the various albumens, it is impossible to assign any number which will bear the test of criticism. For the present, however, this number may be fixed at [_a_]_{D} = -70° for the albumens which remain in solution in the liquids polarized for milk sugar.[200] Many reagents have been prepared for the removal of the disturbing bodies from milk in order to make its polarization possible. Among the precipitants which have been used in this laboratory may be mentioned:[201] (1) Saturated solution basic lead acetate, specific gravity 1.97: (2) Nitric acid solution of mercuric nitrate diluted with an equal volume of water: (=88.=) (3) Acetic acid, specific gravity 1.040, containing twenty-nine per cent acetic acid: (4) Nitric acid, specific gravity 1.197, containing thirty per cent nitric acid: (5) Sulfuric acid, specific gravity 1.255, containing thirty-one per cent sulfuric acid: (6) Saturated solution of sodium chlorid: (7) Saturated solution of magnesium sulfate: (8) Solution of mercuric iodid in acetic acid, formula; potassium iodid, 33.2 grams; mercuric chlorid, 13.5 grams; strong acetic acid, 20.0 cubic centimeters; water 640 cubic centimeters. Alcohol, ether, and many solutions of mineral salts, hydrochloric and other acids are also used as precipitants for albumen, but none of them presents any advantages. Experience has shown that the best results in polariscopic work are secured by the use of either the mercuric iodid or the acid mercuric nitrate for clarifying the milk. The latter reagent should be used in quantities of about three cubic centimeters for each 100 of milk. It is evident when it is desired to determine the residual nitrogen in solution, the former reagent must be employed. The quantity of albuminoid matter left in solution after clarification with mercurial salts is so minute as to exert no sensible effect on the rotation of the plane of polarized light produced by the lactose. For purposes of calculation the gyrodynat of lactose in the ordinary conditions of temperature and concentration may be represented by [_a_]_{D} = 52°.5 (=107=).