Chemistry and Physics. 423 



is sufficient to reply that, in calculatinn^ the result of the experiment, tlie 

 ratio of the densities of air and h3'drogcn raa}' always be taken, so as not 

 to increase the labor of calculation in .the least. Would not, for all 

 chemical purposes, a single uniform system of units be preferable to a 

 mixed system such as that which we now employ? — vr, g,] 



2. On the combinations of ike hydracids tvilh hydrocarhiirets. — Ber- 

 THELOT iinds that the hydrocarburets homologous with olefiant gas, under 

 the influence of heat and pressure, unite with various hydracids so as to 

 form the chlorids, bromids, &c. of the methyl series. Thus propylene, 

 heated for seventy hours to 100° C. with an aqueous sohition of chlor- 

 hydric acid, is completely absorbed, the reaction being expressed by the 

 equation CeHe-f HClzizCeHTOL 



The chlorids, iodids and bromids of amylene, caprylene, ethylene and ace- 

 tene may be formed by precisely similar processes, so that it is possible to 

 pass from the hydrocarburets to the corresponding alcohols by simple and 

 uniform processes. — Comptes Rendus^ xliv, 1350. 



3. On inverse substitutions, — Tho same chemist has also discovered 

 new processes by which iodine, bromine, and chlorine in organic bodies 

 may be replaced by hydrogen. After detailing the processes employed 

 by other chemists in effecting the same object, the author describes his own 

 methods, which consist either in employing free hydrogen at a l\vA\ tem- 

 perature, or in the concuirence of two simultaneous affinities equivalent 

 to the use of nascent hydrogen. Free hydrogen unites with the chlorine 

 of chlorids of carbon at a low red heat, the corresponding carburet of 

 hydrogen being regenerated. A portion of the carburet is always de- 

 stroyed at the same time. Thus we have the equations 



C4Cl44-8n=C4lT4+4HCI 

 C4Cl6+lon=C4H4+GHCl 

 C2oCl9-f 16H=C2oH8-[-8HCl, &c. kc. 



When broraid of ethylene, C4H4l3r2, wvater and iodid of potassium w^ere 

 heated together, hydruret of ethyl was formed, while olefiant gas, car- 

 bonic acid and oxyd, and hydrogen were also set free. The temperature 

 should be near 275° C.and the operation conducted slowly. The bro- 

 mids of propylene and amylene, when heated to 275^ C. with copper, 

 water and iodid of potassium, yield propylene and amylene. By similar 

 processes the author obtained marsh gas from chloroform, bromoform and 

 iodoform. Finally bichlorhydrine, CeHsCls, one of the chlorhydric ethers 

 of glycerine, yields under similar circumstances propylene, Celle, hydruret 

 of propvl, CeHs, hydrogen and carbonic acid. — Conqnes Rendus^ xliv, 



1246^ 1349. 



4. On Silicium and the metallic siliciureis. — Devilie and Cakon have 

 presented to the Academy a memoir upon silicium or silicon which exhibits 

 many points of special interest. Tlie authors find, in the first place, that 

 aluminium is not the only metal which possesses the property of dissolve 

 mg silicon, but that zinc may also be made to act advantageously as a 

 solvent. The preparation of crystalline silicon hy means of zinc is vciy 

 simple and easy of execution. An earthen crucible is to be heated to 

 redness and a carefully made mixture of three parts of fluosilicate of po- 

 tassium, one part of sodium cut in small pieces, and one j^art of granu- 

 lated zinc is to be thrown into it. The reaction ensuing is very feeble 



