28 



PHYSIOLOGY OF NUTRITION. 



colour in half an hour. It is also very instructive to investigate 

 the influence of rays of different refrangibility on crude chloro- 

 phyll solutions. This is the first time we have been confronted 

 with experiments on the influence of rays differing in refrangi- 

 bility ; and hence the method of procedure, of which we shall 

 later have to avail ourselves frequently, must be described in 

 detail. 



An almost concentrated solution of Potassium bichromate, in 

 not too thick layers, transmits red, orange, yellow, and a part of 

 the green, almost un diminished in intensity. An ammoniac al 



Fio. 9. Double-walled bell glass to re- 

 ceive coloured fluids, represented in longi- 

 tudinal section. 



FIG. 10. Glass bottle with parallel walls 

 for the reception of coloured fluids. 



solution of Copper oxide (prepared by dissolving Copper sulphate 

 in water and adding excess of ammonia) absorbs the rays which 

 the Potassium bichromate transmits, but does not arrest the 

 remainder, viz., part of the green, the blue, indigo and violet. 

 With these two solutions, therefore, we are in a position to decom- 

 pose white light almost exactly into a more refrangible and a less 

 refrangible half. To receive the coloured solutions we use very 

 commonly double- walled bell-glasses (see Fig. 9).* The space 

 between the two glass walls, and therefore also the thickness of 

 the layer of coloured fluid, is generally about 1 cm. To prevent 



* Such bell-glasses are to be obtained of Desaga, in Heidelberg. 



