BAIRD &TATLOCK (LONDON) LTD. 



The direction of the oscillations of the light coming through N, and N, form a small angle with one another, the so-called 

 half-shadow. When the oscillations of light coming through the Nicol N, are nearly perpendicular to the bisecting line of this 

 angle, the observer sees both halves of the diaphragm D equally illuminated. This is the zero point of the apparatus. 



To determine the specific rotatory power of a substance, a plane-parallel layer of it is placed between the diaphragms D and 

 A ; liquid substances are placed in tubes which are closed with glass plates. 



For an apparatus with circular divisions (polarising apparatus) the Nicol prism N, and the tube o R is rotated until both 

 halves of the optical field are equally illuminated ; this apparatus requires homogeneous light. With a quartz wedge compensat- 

 ing apparatus (saccharimeter) , the rotation of the active substance is compensated by a corresponding rotation of a quartz plate ; 

 for such instruments white light is used. 



It will be seen that the stand, and more especially the arrangement for reading the scale and vernier, is considerably simplified, 

 as compared with the first and older form of this instrument (loc. cit.). The apparatus consists of a tube support D, at one end 

 of which is the circular scale R and the different eyepieces, whilst at the other end is the triple field polariser p. H is an arrange- 

 ment for altering the intensity of the light passing through the polariser. cc are two parallel triangular shaped runners, fixed 

 on to D, for taking the platform T. The screw q raises or lowers the platform T, so that the observation tube may be brought into 

 the optical axis. The parallel runners cc serve as a base for supporting the rectangular metal jacket G, to be used if observations 

 are to be .taken through wide ranges of temperature. 



APPARATUS FOR ILLUMINATION. 



Hitherto saccharimeters have been illuminated in the following way. A lens fitted to the lamp caused the rays of light to 

 emerge in a parallel state. A system of two lenses projected an image of the flame about midway between the polariser diaphragm 

 (D in Fig. E) and analyser diaphragm (A in Fig. E). With this arrangement the intensity of the light is unequal ; thus, with a 

 small Auer lamp, the polariser diaphragm is generally not uniformly illuminated, whilst any displacement of the ordinary large 

 flame lamps quite appreciably alters the zero point of the saccharimeter. 



F. Lippich has surmounted these difficulties by employing a lens K (Fig. E), which projects the li^ht into the diaphragm of 

 the analyser A. All new instruments made by the firm of Schmidt & Haensch are provided with an illuminating lens of such a 

 focal length that the source o/ light must be at least 14 centimetres distance from the lens. 



LIPPICH POLARISER (half natural size). 





Fig. F represents a Lippich polariser, with the Nicol prisms N 4 and N, and the illuminating 



lens K,. With this arrangement any convenient source of light may be used, such as spectro 



scopically analysed light or electric light. 



Fig. F. 





5841 



58411 P mn r r, 8 t CO i Pe ' I' Schmidt . & Haensch, with double quartz wedge compensator and 

 i on heavy cast-iron stand, provided with fittings for five observation tubes 



&?4S*2L ^^'A* 4 * - ith a second microscope, " 



so 



Lamps for above, Nos. 5855 to 5862. 



143 10 



CROSS STREET HATTCrNT GARDEN, E-C 



1066 



