86 Schmidt & Haensch, Berlin S. 



e) Mitscherlich's Penumbra Apparatus, original construction, 



Fig. 24. 



with Laurent polarizer. With two observation tubes and sodium 

 gas lamp. 



(Eminently suitable for analysis of wine, must etc., Fig. 24.) 



Fig. 25. 



f) Laurent's Penumbra Apparatus, with Laurent polarizer, 

 consisting of a single Nicol and a rock crystal plate, with observing 

 tubes of 220, 200 and 100 mm length and with sodium gas lamp. 



(This apparatus is particularly adapted for exact chemical analysis; read- 

 ing to 1 minute, Fig. 25.) 



