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H. C. VAN DER HEYDE. 



simple chemical reaction. When however we calculate the 

 temperature coefficients we see that they are not constant enough 

 to give us the right to the conclusion that van't HofT's rule 

 holds true in this case, but on the other hand they do not prove 

 the contrary. 



To one remarkable phenomenon which I observed in my 

 experiments I might still draw attention. As stated in my 



FIG. 2. Influence of temperature on the appearance of the yellow pigment of 

 the frog's urine. -4, 11; B, 21; C, 31. As the color of the i urine did not 

 differ from that of 11 only these three have been photographed. 



previous paper pure frog urine as obtained from frogs in the 

 vivarium in which the average temperature is below 10 is 

 absolutely waterclear. Toda and Taguchi however in their 

 paper on the inorganic constituents of the frog's urine observed 

 a slight yellow color. Their experiments were made on summer 

 frogs. Now it is very remarkable that indeed this pigment 

 appeared in my experiments in which higher temperatures were 

 used. Fig. 2 shows a picture of three samples obtained in 

 three different experiments at 11, 21 and 31. The increase 

 in color which was even more striking than this picture shows 

 runs completely paiallel with the nitrogen content as represented 

 in Table I. and Fig. i. 



