80 Scientific Intelligence. 



the silica and get a solution of the bases. Following this method, 

 Hinrichsen observed that the results obtained in determining 

 alumina were sometimes very much too low, even as much as 30 

 per cent of the whole amount. He traced the difficulty to the 

 circumstance that the fluorine is often removed very incompletely 

 by evaporation with sulphuric acid in such cases, and to the very 

 surprising fact, apparently hitherto unknown, that ammonium 

 fluoride interferes with the precipitation of aluminium hydroxide 

 by means of ammonia. In fact, when ammonia was added to a 

 solution of aluminium sulphate, which had been acidified with 

 hydrofluoric acid, no precipitate came down while the liquid was 

 hot, but upon cooling a crystalline deposit of ammonium alumi- 

 nium fluoride, (NH 4 ) S A1F 6 , analogous to cryolite, Na 3 AlF , was 

 obtained. Hinrichsen has made, a quantitative study of this 

 solvent effect of ammonium fluoride and found that 0.6 g. of 

 NH 4 F was sufficient to keep in solution 0.14 g. of A1„0 3 . He rec- 

 ommends avoiding the decomposition of silicates for analysis by 

 means of sulphuric and hydrofluoric acids except in cases where 

 the presence of alkalies makes it " unavoidable." (Like most of 

 the German chemists, he is evidently unfamiliar with the excellent 

 method of J. Lawrence Smith for the determination of the alka- 

 lies.) When the method is used he advises evaporating off the 

 sulphuric acid completely and gently igniting the residue, in 

 order that the fluorine may be completely removed. 



The interesting and important fact disclosed by Hinrichsen's 

 work led the writer of this notice to confirm it by qualitative 

 experiments. It was found that while ammonium fluoride readily 

 prevents the precipitation of aluminium hydroxide by ammonia, 

 this is not the case with ferric hydroxide, and further that the 

 addition of a soluble phosphate to such a solution causes the 

 precipitation of aluminium phosphate. It appears possible that a 

 method for the separation of iron and aluminium might be based 

 iipon this behavior, the aluminium to be precipitated as phosphate 

 and weighed as such. — Berichte, xl, 1497. h. l. w. 



3. Magnetic Compounds of Manganese with Boron, Anti- 

 mony and Phosphorus. — Until a few years ago the only magnetic 

 metallic substances known were iron, nickel and cobalt. Then 

 several alloys of non-magnetic constituents were found to be 

 strongly magnetic, all of which contained manganese, viz., man- 

 ganese-tin, manganese-aluminium and manganese -aluminium- 

 copper. It appears, however, that Wohler had noticed nearly 

 50 years ago the first case of a magnetic compound of non-mag- 

 netic elements in the oxide of chromium Cr 5 9 . Wadekind has 

 recently found that the boride of manganese, MnB, has remark- 

 ably strong magnetic properties, probably one-quarter to one- 

 half as great as soft iron, while the compound MnB 2 does not 

 appear to be magnetic at all. The antimonide, MnSb, seems to 

 be about twice as strongly magnetic as the bofide, while the 

 phosphide Mn 3 P 2 shows this property to a much slighter extent. — 

 Berichte. xl, 1259. H. L. w. 



