388 Scientific Intelligence. 



gen would produce a high pressure ; but even at a calculated 

 pressure of 60 atmospheres the appearance of the products did 

 not change. These experiments indicate that free ammonium is 

 incapable of existence even at — 70° and at a high pressure. — 

 JBerichte, xxxiv, 2604. h. l. w. 



3. A Modified Gooch- Crucible. — W. C. Hekaeus is manufac- 

 turing filtering crucibles, the bottoms of which are made of 

 spongy platinum. This device was suggested to the manufac- 

 turer by Dr. Neubauer of Breslau and is called the Neubauer 

 crucible. It is stated that the porous bottom is strong, and that, 

 with reasonable care, precipitates may be scraped off with a 

 spatula. The crucible filters rapidly with a good suction-pump, 

 and yet retains the finest precipitates, such as freshly precipitated 

 barium sulphate and silver chloride. Such exceedingly fine pre- 

 cipitates and gelatinous ones, however, soon form a layer through 

 which the liquid cannot pass, so that this modification has the 

 same limitations in filtering as the ordinary Gooch-crucible where 

 an asbestos filter is used. The Neubauer crucible possesses the 

 disadvantage that it cannot be used for filtering and igniting 

 precipitates which cannot be dissolved out of the porous platinum. 

 It is stated that, on this account, barium sulphate should not be 

 weighed in these crucibles ; but, since this substance is readily 

 soluble in hot, concentrated sulphuric acid, there is no doubt that 

 it would present no obstacle to a chemist acquainted with the 

 proper solvent. The advantages of nearly constant weight, and 

 of the possibility of dissolving precipitates in hydrofluoric acid, 

 appear to be the chief reasons for using the new device in prefer- 

 ence to the customary one. — Zeitschr. fur angewandte Chemie, 

 xxxvii, 923. h. l. w. 



4. Radio-active Lead. — It has been mentioned previously in 

 this department of the Journal that Hofmann and Strauss have 

 obtained radio-active lead salts from various rare minerals. These 

 authors have recently described further investigations upon the 

 subject, and are still of the opinion that this radio-active sub- 

 stance differs in many respects from ordinary lead in its chemical 

 behavior, but they have not yet obtained it in a pure state. They 

 find that, while the various salts of radio-active lead have nearly 

 the same action upon the electroscope, only the sulphate is 

 capable of acting upon the photographic plate through glass or 

 aluminum ; moreover, the sulphate becomes particularly active 

 in the latter respect after having been evaporated with nitric and 

 sulphuric acids, or after having been ignited at 450° for 15 hours 

 with access of air. ^ It appears also, that while radio-active lead 

 sulphate acts more energetically upon the photographic plate 

 than certain polonium (radio-active bismuth) preparations, the 

 latter have a much greater action in discharging the electroscope. 

 The authors believe that it follows from this that the rays 

 detected by photographic means are not identical with those 

 which pro'duce electric discharges. — Berichte, xxxiv, 3033. 



H. L. W. 



