Chemistry and Physics. 465 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. On the Vapor-density of Aluminum chloride. — The experi- 

 ments of Nilson and Pettersson (Zeitschr. pbys. Chem., i, 459) 

 seemed to show that aluminum chloride when heated in an at- 

 mosphere of carbon dioxide gave, at a temperature of about 835°, 

 a vapor-density corresponding to the formula A1C1 3 ; and this 

 without evidence of decomposition, although above 935° the plat- 

 inum vessel was attacked. Friedel and Crafts have pointed 

 out that exact results are obtained with V. Meyer's method 

 (which was the one used by Nilson and Pettersson) only when 

 there is no diffusion of the vapor into the air of the apparatus. 

 And they have therefore re-determined the vapor-density of alu- 

 minum chloride by the method of Dumas, taking great care to 

 obtain and to maintain the substance perfectly anhydrous. The 

 aluminum chloride was obtained by sublimation in large, color- 

 less and comparatively non-hygroscopic crystals, which though 

 volatilizing directly without fusion at ordinary pressures, melt 

 at about 186° under a pressure of 2*5 atmospheres. The vapor- 

 pressure of this substance was found to be 252-1 mm. at 167'8°; 

 31T4 mm. at 170-4°; 316*5 mm. at 171-9°; 430*7 mm. at 175"7°; 

 755-4 mm. at 182-7°; 1793-4 mm. at 204-2°; 2016-1 at 207*5°; 

 and 2277*5 mm. at 213*0°. The temperatures at which the vapor- 

 densities were determined were 218°, 263°, 306°, 357°, 390°, 398°, 

 400°, 415°, 429° and 433°; and the results agreed closely with 

 the density 9*24, the value corresponding to the formula A1 2 C1 6 ; 

 thus confirming the earlier results of Deville and Troost. Since 

 the lowest temperature at which Nilson and Pettersson operated 

 was 440°, it may be that the lower values obtained by them are 

 due to a dissociation of the molecule A1 2 C1 6 into (A1C1 3 ) 2 analo- 

 gous to that of iodine, or into A1 2 C1 4 and Cl 2 as in the case of fer- 

 ric chloride. The authors' experiments prove, however, that alu- 

 minum chloride becomes a perfect gas at 218°, or 35 degrees 

 above its boiling point; and that the density of this vapor is sen- 

 sibly the same up to 400°. Hence they conclude that the formula 

 of this substance is A1 2 C1 6 ; a conclusion in agreement with the 

 determinations of Louise and de Roux of the vapor-densities of 

 aluminum methide and aluminum ethide. — C. R., cvi, 1764; J. 

 Chem. Soc, liv, 1040, Oct., 1888. G. f. b. 



2. On Freezing mixtures containing solid Carbon dioxide. — 

 Cailletet and Colardeatt have determined the temperature of 

 solid carbon dioxide, alone as well as when mixed with other 

 suitable substances, in air and in vacuo. For this purpose they 

 used a thermo-electric couple which had been calibrated by com- 

 parison with a hydrogen thermometer. The carbon dioxide alone, 

 either compressed or porous, when exposed to the air, had a tem- 

 perature — 60° and when in a vacuum over potassium hydrate, 



