(33) 



I have tried to find a meltingpoint-line of the already desci-ibed type 

 in the monoclinic derivatives in which some degree of form-analogy 

 is noticeable. However, in none of the three binary mixtures this 

 was the case ; the lower melting point was lowered on addition of 

 the component melting at the higher temperature, without formation 

 of mixed crystals. For instance : 



A mixture of 82,37o J-2-3- and 17, 7 y,l-3-5'Nitrodibromo-benzene 

 melted at 487,° C. 



A mixture of 76,57o 1-2-6- and 23,57„ l-Z-D-Nitrodibro7no-benzene 

 at 687,° C. 



A mixture of 90,57o 1-3-4- and 9,57o i-2-G-Mtrodibromo-benzene 

 at 54° C. 



Moreover, no mixed crystals could be obtained from mixed solutions. 



The slight form-analogy with the N itro-dichloro-benzenes ^) investi- 

 gated by me some time ago is rather remarkable. 



Nitro-%'^-Dichloro-Benzene (62° C. rhombic) and Nitro-1-Q-Dichloro- 

 Benzenc (71° C. monoclinic) exhibit practically no form-analogy with 

 the two Dlbivmo-compoumh. There is also nothing in the Dichloro- 

 derivatives corresponding with the isomorphotropous mixture of the 

 2-3- and 2-5-Z)/6römö-product. The sole derivatives of both series 

 which might lead to the idea of a direct isomorphous substitution 

 of two CI- by two i>r-atoms are the Nitro-'6-^-Dihalogen-Benzenes 

 (65° C. and 104°, 5 C); the melting point of the Z)/c/i/o?'ö-derivative 

 is indeed elevated by an addition of the Dibromo-éQv'waiivQ. 



As a rule, the differences in the crystal-forms of the compounds 

 of the brominated series are much less than those between the forms 

 of the chlorinated derivatives — a fact closely connected with the 

 much greater value which the molecular weight possesses in the 

 Nitro-Dibrorno-Benzenes than in the corresponding C%/(>?'o-derivatives. 



Zaandam, April 1906. 



Physiology. — ''On the nature of precipitin-reaction." By Prof. 

 H. .1. Hamburger and Prof. Svante Arrhenius (Stockholm). 



(Communicated in the meeting of April 27, 1906). 



One of tiie most remarkable facts discovered during the last years 

 in the biological department, is most certainly the phenomenon that 

 when alien substance is brought into the bloodvessels the individual 

 reacts upon it with the forming of an antibody. By injecting a 



1) These Proc. VII, p. GG<S. 



3 



Proceedings Royal Acad. Amsterdam. Vol. IX. 



