33 



salts described b}- Scheibk') in 1879 and 1880, with the excepiion 

 however of a potassium salt, which was considered to have the 

 formula Ci,H,,K(BO),0,,, . 2H,0, crystallizes beantifnlly, and to 

 which we refer below'). 



Also among tlie salts of boro-salicylic acid described for the first 

 time by Jahns in 1878') there are some well-crystallised compounds. 



The tirst who inquired more systematically into the intluence on 

 the acidity of boric acid by hydroxyl-containing suiistances, was 

 Magnanini, who pnblislied a series of papers on the intluence which 

 these substances have on the conductivity (and some other physical 

 constants) of boric acid solutions.'') The number of compounds 

 examined by him is very large, and he pointed out the intluence of 

 the constitution in connection with the occurrence or non occurrence 

 of an increase of conductiviiy. He found a.o. that this was only 

 olisei'ved in a-o\y acids, and not when the OH-gi-onp is somewhere 

 else, it WHS found in aromatic ö-oxy carbonic acids, not in the ?h- 

 and /j-isomers, it was found in ö-diphenols, not in m- and />diphenols. 



These researches have been continued and extended by Boeseken 

 (and collaborators)"), who assumed, discovered, and worked out an 

 intluence of the steric configuration by the side of the constitional 

 influence. 



In his hands the Magnanini "boric acid method" became an im- 

 portant instrument, not only for the determination of the constitution 

 and configuration, but also for our stereo-chemical views in general. 

 These results reached their acme in the application of the method 

 to the sugars and their derivatives, the isomeric tartaric acids, and 

 the saturated cyclic vie. diols. 



In his "Lagerung der Atome im Raume'' Van 't Hokf already 

 expressed his opinion that in the compounds which are responsible 

 for the phenomena in question, the boron atom might be part of a 

 ring-system, and that this ring could close only when certain condi- 



1) Russ. Zeitschr. f. Pharm. 18, 257, 289, 321 ; 19, 513. Pliarm. Journ. and 

 Trans. (3) 11. 889. 



') We have not yet been able to test entirely the records given by Klein in 

 1878 on mannite-boric acid salts of rather complicated constituliou. Probably we 

 have to do with not accurately defined substances also here. 



') Arch, der Pharm. (3) 12, 212. 



*) Z. phys. Gh. 6, 58. Gazz. chim. Ital. 20, 441, 448, 453; 21, 184, 215; 22, 

 541; 23, 197. Acad, dei Lincei Rend. (4) 6a, 411, 457. 



5) E.g. These Proc. Vol. XV, p. 216 (1912); Vol. XVIII, p. 1647, 1654 (1915); 

 Vol. XXI, p. 80 (1918); Vol. XXIII, p. 69 (1920); Verslag van de gewone ver- 

 gaderingen K. Akad. v. Wet. Amsterdam Dl. XXIX, p. 368, 924 (1921). Ghem. 

 VVeekbl. 19, 207. Recueil 40, 354, 558. 



3 



Proceedings Royal Acad. Amsterdam. Vol. XXVI. 



