64 Scien tific hi telligen ce. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. Probable Source of the Heat of Chemical Combination^ and 

 a Neio Atomic Hypothesis. — Professor T. W. Richards has 

 brought forward the very suggestive generalization that the con- 

 traction exhibited during chemical combination is in many cases 

 approximately proportional to the heat evolved; hence he be- 

 lieves that the chief source of heat of chemical combination is 

 the work performed in compressing the material. He gives an 

 explanation upon the same basis of the mechanism of the heat of 

 adsorption, adhesion and changje of allotropic form. He is led, 

 from these considerations, to the interesting hypothesis of com- 

 pressible atoms, for the details of which, with ingenious applica- 

 tions, reference must be made to the original article. — Proc. 

 Amer. Acad., xxxvii, 399, and Zeitschr. x)hysikcd. Chem., xl, 597. 



H. L. W. 



2. Lithium Silicide. — By heating silicon with metallic lithium 

 in a nickel boat in an exhausted tube, Moissax has found that the 

 two elements combine and that the excess of lithium used may be 

 distilled off between 400 and 500°, leaving a bright indigo-blue 

 product in the form of brilliant crystals. The compound has the 

 composition represented by the formula Si^Li^ and corresponds to 

 the spontaneously-inflammable hydride of silicon, Si^H^, which 

 was i-ecently described by Moissan and Smiles. The lithium 

 silicide is very hygroscopic, is violently decomposed by water, 

 acids and the halogens, and, as would be expected, has very 

 powerful reducing properties. Thus, when heated with the 

 oxides of iron, chromium, manganese and calcium it gives the 

 metals or alloys, but it does not decompose alumina. — Comptes 

 Pendus, cxxxiv, 1083. h. l. w. 



3. The Black Color of the Pocks in the Cataracts of the Nile. 

 — LoRTET and Hugounenq state that the rocks in the Nile rapids 

 at Wady-Halfa and at Assouan, which are covered at the time of 

 high water, are very smoothly polished and present a deep black 

 color when visible at low water. This is not due to the colors of 

 the rocks themselves, which are eruptive rocks and sandstones of 

 various colors, but to a thin black coating. When this surface 

 is treated with strong hydrochloric acid a brown liquid is obtained 

 which loses its color upon heating, chlorine is given off and the 

 liquid gives reactions for manganese. This shows that the black 

 coating is due to manganese dioxide. The rocks contain small 

 quantities of manganese not in the form of dioxide, but the lat- 

 ter is produced upon their polished surfaces. — Comptes Pendus., 

 cxxxiv, 1091. H. L. w. 



4. Pismuth-lead Sulphide-hcdides. — Three compounds, made 

 \)j fusing lead halides with bismuth sulphide, have been described 

 by DucATTE. They form very small acicular crystals in the 



