44 



A. Kriiss, Hamburg. 



The telescope is moved by means of a micrometer screw and the amount 

 of movement is read off a divided drum; also the width of the ocular slit and 

 the travel of the cross lines can be measured bv means of a divided drum. 



Fig. 3. 



The slit, by a very simple arrangement, opens symmetrically with respect 

 to the optical axis. 



C. H. Wolff's Colorimeter. (Fig. 4.) 



This instrument is intended for colorimetric 

 determination of the concentration of coloured 

 liquids by comparison with a standard solution. 

 The light is, by means of a mirror placed below 

 the measuring cylinders, reflected through the 

 latter, and, by means of two reflecting prisms, 

 the two pencils are made to illuminate the two 

 halves of the field of a lens. From the darker 

 liquid as much is allowed to flow off as is ne- 

 cessary to render both halves of the field equally 

 bright. The respective concentrations of the li- 

 quids are than in the inverted ratio of the heights 

 of the liquid columns. 



This colorimeter may be used for all colo- 

 rimetric tests in analytical chemistry, e. g. for 

 determining the percentage of ammonia in water, 

 for examination of nitrous acid, for selecting 

 colours or salicilic acid, for quantitative deter- 

 mination of slight admixtures of copper, zinc, 

 chlorine compounds etc. 



