METHODS OF STUDYING VISION IN ANIMALS 



41 



and nuts. The clear aperture of this cell is lo x lo cm. 

 In the form used by us, it carries a 2 cm. layer of solution, but 

 it may as readily be made for a i cm. layer. 



At the outset of this investigation it was our ambition to 

 select a set of wet filters which should yield the principal spectral 

 hues in a satisfactory manner. This we have not succeeded in 

 doing, and we therefore present the following formulae — all 

 of which have proved satisfactory under certain circumstances 

 — for the consideration of those who wish to experiment with 

 wet filters. 



The formulae of Landolt.' — These we have tested and found 

 airly satisfactory with respect to the quality of the light trans- 

 mitted. The yellow is unsatisfactory because of the low intensity 

 of the transmitted light. 



Thick- 

 ness of 

 layer in 

 Color mm. 



Red 



Aqueous solution 



20 Crystal violet 5 Bo. 



Grams of Optical 



substance point of 



in 100 cc. max. value 

 of solution 



o .001:; 



66s -9 i^f^ 



.20 Potassium monochromate. 10 



Yellow 



C20 Nickel sulphate + 7 aq. 

 15 Potassium monochromate. 

 15 Potassium permanganate. 



10 591.9/^/^ 



0.025 



Green 



r20 Copper chloride +2 aq. 

 I20 Potassium monochromate. 



60 



10 



533 -o ^'^ 



Light blue 



Dark blue 



'20 Doppelgrun S, P". 



.20 Copper sulphate + 5 aq. 



^20 Crystal violet 5 BO. 



.20 Copper sulphate + 5 aq. 



o . 02 



15- 



o .005 



15 



488 . 5 A'/A 



448.2 /^/A 



' H. Landolt. Das optische Drehungsvermogen. 2 Auflage, Braunschweig, 

 1898, S. 390. 



