Chemist?'y and Physics. 323 



All the Xalostoc crystals I have seen are rhombic dodec- 

 ahedrons (i) ; many of them have a tolerably distinct dodeca- 

 hedral cleavage. Their hardness is 7'5, and their fusibility a 

 little below 3. By fusion before the blowpipe a yellow glass 

 is obtained ; before Fletcher's hot blast blowpipe, fusion is 

 accompanied by intense glowing and a white blebby glass is 

 obtained. 



Guadalajara, Mexico, February 18th, 1891. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. On the Determination of Vapor-Pressures.— A new method 

 for determining the vapor-pressures of solutions has been de- 

 scribed by Chakpy. The solution to be examined is contained 

 in a large test tube, in the upper portion of which a small con- 

 densation hygrometer is placed. After allowing the space above 

 the liquid to become saturated with the vapor of the solvent, 

 accelerating the process by reducing the pressure if necessary, 

 the dew point is determined. Knowing the law according to 

 which the vapor-pressure of the solvent varies, the vapor-pressure 

 of the solution at the temperature of the experiment can be 

 readily calculated. The accuracy of the determination is the 

 greater, the less the pressure that is to be measured. One ad- 

 vantage of this method is the fact that it may be applied to 

 solutions which attack mercury and cannot in consequence be in- 

 troduced into a barometric tube. — C. P., cxi, 102 ; J. Ghem. Soc, 

 lviii, 1364, Dec. 1890. o. f. b. 



2. Vapor-densities at low Temperatures. — The method of 

 Demuth and Meyer for determining vapor densities below the 

 boiling point,* has been found by Krause and Meyer to be still 

 applicable when in place of hydrogen, other gases such as air, 

 nitrogen or even carbon dioxide, are used to fill the vaporizing 

 bulb. Although the vaporization is then much slower, perfectly 

 accurate results are obtained ; as the authors have shown by their 

 determinations of the vapor-density of xylene at 40° below its 

 boiling point and of paranitrotoluene at 33° below, in air and in 

 carbon dioxide. It is preferable to use hydrogen however in all 

 cases where it is practicable. Experiments made by the authors 

 show that the theoretical vapor-density of acetic acid is reached 

 at about 160°; the values obtained steadily diminishing from 

 2-60—2-67 at 100°, to 2'12— 2*18 at 160° and 2'07— 2'14 at 190° ; 

 the theoretical vapor-density being 2*08. Cahours, using the 

 method of Dumas, reached the theoretical vapor density of acetic 

 acid, only at 250°. Iodine allowed to vaporize at the tempera- 



* See this Journal, III, xxxix, 312, April, 1890. 

 Am. Jour. Sgi.— Third Series, Vol. XLI, No. 244. — April, 1891. 

 21 



