The chemistry of essential oils and artificial perfumes : illustrated with engravings / by Ernest J. Parry.

  • Parry, Ernest J. (Ernest John)
Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: The chemistry of essential oils and artificial perfumes : illustrated with engravings / by Ernest J. Parry. Source: Wellcome Collection.

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    tain position with reference to the polariser and plate, the two halves of this plate appear equally illuminated. By adjusting the prisms by means of the movable pointer, H, and the screw, E, which govern the delicacy of the instrument, the zero marks on the dial and on the vernier are made to correspond when the position of equal illumination is attained. A slight rotation of the analyser in either direction by means of the projecting screw handle at once causes the two halves of the field to become unequally illuminated. Having set the instrument at zero, a tube containing an optically active liquid is inserted in the groove, E. It will now be found that the analyser has to be rotated a certain nurnber of degrees either to the right or the left in order to restore the position of equal illumination of the two halves of the field. This is the angle through which the plane of polarisation has been rotated. The beginner will find a little difficulty in using this instrument; for example, when examining oils with high rotations or when the dial has been rotated too far, and has been taken beyond the range of sensitiveness ; half an hour with some one who understands the instrument will explain its use far better than pages of printed matter. The rotation of the dial in the direction of the movement of the hands of the clock, as the observer sees it,- is conventionally termed dextro-rotation, and conversely. In general, the optical rota- tion is expressed for a column of 100 millimetres. The specific rotary power is a different figure, it is expressed by the symbol [a], and, taking the decimetre as the unit of length for this purpose, is the observed rotation in the decimetre tube divided by the specific gravity of the liquid. The molecular rotation, refers of course only to pure compounds and not to mixtures, and need not be discussed here, other- wise than to mention that it is the product of the specific rotary power and the molecular weight. In the sequel, the , optical rotation will be understood to refer to the rotation
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