Text-book of medical and pharmaceutical chemistry . lled withthe solution to be tested and again placed between the analyzerand polarizer, when, if it is an active substance, the plane of thepolarized ray coming from the analyzer will be turned to the right,or to the left, in passing through the solution, and one-half of thefield will be lighter than the other. The amount of rotation ofthe plane of the polarized ray will be proportional to the amountof the active substance in the solution. It will now be neces-sary to rotate the analyzer (B) to the right or to the left, so thatthe two halves o
Text-book of medical and pharmaceutical chemistry . lled withthe solution to be tested and again placed between the analyzerand polarizer, when, if it is an active substance, the plane of thepolarized ray coming from the analyzer will be turned to the right,or to the left, in passing through the solution, and one-half of thefield will be lighter than the other. The amount of rotation ofthe plane of the polarized ray will be proportional to the amountof the active substance in the solution. It will now be neces-sary to rotate the analyzer (B) to the right or to the left, so thatthe two halves of the field will again appear equally this has been accomplished, we may read off on thevernier the degrees of the circle through which the analyzer hasbeen rotated. In this way the amount of rotation of the polar-ized ray is determined. LIGHT, 43 48. The specific rotatory power of any substance is theamount of rotation of the plane of polarized light, in degrees ofa circle, produced by i grm. of the substance dissolved in i c. of the liquid, examined in a tube i decimeter in length. Thespecific rotatory power of a substance is obtained by dividing 44 MEDICAL CHEMISTRY. the angular rotation observed in the polarimeter, (a), by thelength of the tube in decimeters (1) and by the number of I c. c. of the liquid (w). If a sodium flame be used asa source of light, the specific rotation of the substance is that oflight with wave length corresponding to the D line of the solarspectrum, and is usually denoted by (a)^. Then the abovemay be stated as follows:— (a)D = wl. In this formula plus indicates that the substance is dextrorota-tory and minus that the substance is levorotatory. If in thisformula the specific rotatory power of the substance underexamination be known and we wish to find the value of (w), orweight of the substance, then the formula becomes: a, in this formula, is the observed rotation, 1 the length of the tubein decimeters, which is kno
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