252 Scientific Intelligence. 



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Zeitschr. physikal. Chem., ix, 563, June 1892; J. Ghem. Soc, lxii, 

 1149, Oct., 1892. Cx. F. b. 



2. (?;? tfAe Permeability of Precipitated Membranes. — As long 

 ago as X^^i, Traube expressed the opinion that precipitated mem- 

 branes are porous, the pores allowing the smaller water molecules 

 to pass but not the larger molecules of the dissolved substance ; 

 the membrane acting like a sieve. In 1890, Ostwald modified this 

 view by suggesting that the permeability of the membrane re- 

 ferred, not to the salt molecules as a whole but rather to their 

 ions. So that a salt, both ions of which can traverse the membrane, 

 can pass through it as a whole; while if one of the ions is stopped 

 by the membrane, the salt itself is also stopped. Tammann has 

 tested these views experimentally, by preparing three membranes, 

 tannate of gelatin, zinc ferrocyanide and copper ferrocyanicle, and 

 then determining their permeability to seventeen acids and salts 

 in solution in water. In accordance with the molecular sieve 

 theory, the order of permeability of the three membranes was 

 found to be the same for all the substances dissolved. Moreover, 

 it was found that acids diffuse through a copper ferrocyanide 

 membrane in the order of their strength ; i. e. of the degree of 

 their dissociation into ions, thus indicating that it is rather the 

 ions that pass through the membrane and not the acid itself. 

 The diffusibility of hydrochloric acid being 9*0, that of trichlor- 

 acetic acid was found to be 6'6, of monochloracetic acid 3-3 and 

 of acetic acid 2*6. Experiments with a large number of salt solu- 

 tions, to determine their power to pass through different mem- 

 branes, gave anomalous results. Thus while the chlorides, bro- 

 mides and nitrates of potassium, ammonium, sodium and lithium 

 pass readily through membranes of copper ferrocyanide, the cor- 

 responding sulphates diffuse with much greater difficulty, and the 

 membrane is impermeable to salts of calcium and magnesium, 

 although it allows the diffusion of the chlorides and bromides of 

 barium and strontium. Moreover, while succinic, tartaric, citric 

 and isobutyric acids diffuse through the membrane, their potas- 

 sium salts do not. Evidently the views of both Traube and 

 Ostwald require modification. The author thinks the phenomena 

 of diffusion may be due to solution, since all these semi-permeable 

 membranes are strongly hydrated. — Zeitschr. physikal. Chem., x, 

 255, Aug. 1892; J. Chem. Soc, lxii, 1383, Dec. 1892. g. f. b. 



3. On Fluosxdphonic acid. — It has been shown by Gore that 

 when liquid hydrogen fluoride is brought in contact with sulphur 

 trioxide, it acts upon it with great violence. Thorpe and Kir- 

 man have studied this reaction and have shown that when the 



