468 Intelligence and Miscellaneous Articles. 



ments. The corrected volume of hydrogen was 85*3 cubic centim., 

 which multiplied by 4 gives no less than 341*2 cubic centim. of 

 hydrogen from 6*4790 grammes. This is about seven times the 

 amount afforded by the original dust, and 3*8 times more than the 

 mean of the results obtained with the dust which had been wetted. 



Experiment XL — In this experiment, in which, the full heat of a 

 strong Bunsen flame was kept until the volume of hydrogen ceased 

 perceptibly to increase, 90*7 cubic centim. of hydrogen were ob- 

 tained from 1-6198 grammes, or 362-8 cubic centim. from 6-4790 

 grammes = 100 grains. 



The above results confirm in the strongest manner the views I 

 had entertained as to the source of the hydrogen in zinc dust, and 

 conclusively show that exposure to a moist atmosphere at a mode- 

 rate temperature is eminently favourable to the condensation of the 

 hydrogen. It is not improbable that, by suitably modifying the 

 conditions, this amount may be exceeded. As zinc dust thus 

 charged with hydrogen can hardly fail to become an important 

 chemical reagent, I shall endeavour to determine the maximum 

 amount that can be occluded, and the ratio to the amount of 

 metallic zinc present. — Journal of Gas Lighting, Oct. 13, 1885. 



ON TWO NEW TYPES OF CONDENSING HYGROMETERS. 

 BY M. G. SIRE. 



The accuracy of condensing hygrometers is known to depend on 

 the exactitude with which we observe the temperature of the 

 surface on which dew is deposited as well as on the more or less 

 distinct perception of this deposit. 



I have succeeded in rendering these determinations very distinct 

 by observing the deposit of aqueous vapour on a cylindrical or a 

 plane brilliant surface, which gives rise to two new types of con- 

 densing hygrometer, where the fall of temperature is produced by 

 the evaporation of ether in which is a thermometer. 



The reservoir of the first type consists of a cylindrical tube of 

 thin polished metal, the ends of which are insulated in the interior 

 by two pieces of ebonite, so that the volatile liquid is only in con- 

 tact with the metal side by a middle zone of about 1 centim. in 

 height. On this zone the dew is deposited ; it shows itself by a 

 whitish ring which appears at half the height of the reservoir. 



The reservoir of the second is entirely of ebonite ; it is traversed 

 laterally by a circular aperture closed by a thin metal disk, polished 

 on the inside. On the part of this disk which closes the aperture 

 the dew is deposited, forming a dull white circle m the centre ; 

 under a certain angle the disk appears of a pure black. 



The bright surfaces are obtained by an electrochemical deposit 

 of palladium ; the black polish of this metal reveals the slightest 

 traces of condensation. 



The essential character of these hygrometers is that the deposit 

 is made in the centre of a brilliant metal surface without a break. 

 On the other hand, the agitation of the liquid and the thinness of 

 the sides ensures perfect equality of the two parts in each instru- 

 ment.— Comptes liendus, Sept. 28, 1885. 



