Chemistry and Physics. 613 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. An Apparatus for Determining \ Molecular Weights and 

 Hydrogen Equivalents. — W. H. Chapin of Oberlin College has 

 devised an interesting method for the determination of the 

 molecular weights of organic liquids whose boiling-points are 

 below 90° C, and for determining the hydrogen equivalents of 

 such metals as zinc, aluminium, sodium and calcium. The 

 method depends upon measuring the pressure produced by the 

 volatilization of the liquid or by the formation of the gas, and 

 since the apparatus is very simple and can be made from the 

 materials usually at hand in chemical laboratories, the process 

 should be very useful for lecture demonstrations and for stu- 

 dents' laboratory work. 



The apparatus consists of an ordinary distilling-flask of 600 cc. 

 capacity, of which the side tube is cut off and replaced by a 

 glass manometer tube with a bore of about 7 mm. and a vertical 

 height of about 20 cm. The manometer is charged with mer- 

 cury and hangs perpendicularly at a little distance from the 

 bulb of the flask, so that its position is outside of a beaker used 

 in molecular weight determinations as a steam-bath. The steam 

 is supplied by boiling some distilled water in the bottom of the 

 beaker, and the latter is supplied with a cover of sheet-zinc made 

 in two parts so that it fits the lower part of the neck of the flask. 

 The capacity of the flask including its neck is found by weighing 

 it full of water. The average temperature of the interior of the 

 flask when heated by steam is found by means of a thermometer 

 placed at different levels in the bulb and the neck, with due 

 allowance for their capacities. The mouth of the flask is pro- 

 vided with a stopper containing a tube with a sliding rod 

 extending into it from a side branch above the stopper for 

 dropping in the weighed substance according to the arrange- 

 ment commonly used in the Victor Meyer apparatus. The 

 author has used as containers for the organic liquids experi- 

 mented upon small gelatine capsules previously dried at 100° C. 

 The change in level of the mercury is read by means of a celluloid 

 millimeter-scale clamped to the manometer. 



For the determination of hydrogen equivalents of metals, 

 weighed quantities of the latter are dropped into dilute acids, or 

 in the case of sodium into absolute alcohol, at ordinary tempera- 

 tures while the beaker is kept full of water for maintaining a 

 constant, known temperature. It is advisable to wind copper 

 wire around the pieces of zinc employed in order to facilitate 

 their solution. 



The calculations are simple, since the weights of substances, 



