240 Scientific Intelligence. 



formerly all the carbon in the earth existed in the form of car- 

 bides, and that these have been gradually decomposed by the 

 action of water. — Zeitschr. fur Electrochem., viii, 44. h. l. w. 



3. Potassium Hydride. — It has been found by Moissan that 

 the action of hydrogen upon metallic potassium at 360° gives a 

 white compound which sublimes in crystals and has a composi- 

 tion corresponding to the formula KH. The substance is exceed- 

 ingly sensitive to the action of moisture, and it takes fire at 

 ordinary temperature when exposed to fluorine, chlorine or dry 

 oxygen. It seems probable that Gay-Lussac and Thenard's sup- 

 posed compound K 2 H was a mixture of the true hydride with 

 metallic potassium, since Moissan has found that the action of 

 hydrogen on potassium is very slow. — Comptes Pendus, cxxxiv, 

 18. h. l. w. 



4. On Electrical Conductivities produced in Air by the Motion 

 of Negative Ions. — Professor Townshend (Phil. Mag., Feb., 

 1901) has shown that negative ions produced in a gas are capable 

 of disintegrating other molecules by collision, and thus of gener- 

 ating other ions. This subject has been further studied by P. J. 

 Kirkby, whose experiments confirm Professor Townshend's 

 general result, who finds that there is a remarkable difference in 

 the behavior of positive and negative ions when moving in a 

 small pressure under electric force. The negative ions have the 

 property of disintegrating other molecules when colliding with 

 them, while the positive ions do not appear to have this property. 

 Professor J. J. Thomson has found from experiments with ultra 

 violet light the mass of the negative ion to be 3 X 10~ 26 of a gram. 

 Professor Townshend finds 4 - 5XlO~ 24 as the weight of a mole- 

 cule of hydrogen. This makes 6*6 X10~ 23 as the corresponding 

 weight for air, which is more than three times the number given 

 by Meyer (Kinetic Theory of Gases, art. 121). If it is assumed 

 that the negative ions produced by the Rontgen rays are identi- 

 cal with those produced by ultra-violet, the molecules of air 

 are 2200 times the size of the negative ion according to the above 

 numbers. If the positive ion is what remains after the negative 

 ion is detached from it, it follows that the positive ion does not 

 materially differ in mass from the ordinary molecule in air. It 

 far exceeds in magnitude the negative ion, and the mean path of 

 the latter exceeds that of the former. Professor Townshend 

 finds -4l mm as the path of the negative ion in l mm pressure of air. 

 The corresponding path of the positive assumed to be equal to 

 that of the molecule of air is about '094 of a millimeter. This 

 must be multiplied by V" 2 when the ion is moving under elec- 

 tric force.— Phil. Mag., Feb., 1902, pp. 212-225. j. t. 



5. On a kind of Radio-activity imparted to certain Salts by 

 Cathode Pays. — Dr. J. C. McLennan gives in this paper an 

 account of a research which shows that certain salts which show 

 no radio-activity as ordinarily prepared exhibit this property in a 

 very marked manner on being gently heated after exposure to 

 cathode rays. The radiation emitted was sufficient to discharge 



