394 Intelligence and Miscellaneous Articles. 



of the pressure. I have been prevented by circumstances from 

 completing this investigation. Very special care was devoted to 

 the dryness of the air. For this purpose it passed through potash 

 and sulphuric acid into a large glass receiver, the bottom of which 

 was covered with anhydrous phosphoric acid; the air-thermo- 

 meter was not filled with this until it had been stored for several 

 days. The agreement between the coefficients with the various 

 fillings was nevertheless insufficient; it varied for atmospheric 

 pressure between 3667 and 3676. 



I imagined now that the air of the town might contain variable 

 quantities of hydrocarbons; in order to eliminate this factor I 

 passed the air through a hard-glass tube containing platinum wire, 

 which was kept heated by a lamp placed underneath it. The air 

 passed afterwards through caustic potash and sulphuric acid into 

 the reservoir. When air was taken from this twenty-four hours 

 afterwards the coefficient of tension was found to be 3731 : air 

 taken from the same reservoir six days afterwards, 3669. I then 

 made several such determinations, of which I will mention one : 

 the reservoir was filled after using the platinum wire ; air removed 

 twelve hours afterwards gave 3767, after three days 3673, and 

 after six days 3670. 



It appears thus that air which has passed over heated platinum 

 has apparently a very high coefficient of tension, but after long 

 standing it loses this property. This is explained by the fact that 

 particles are detached from the platinum which are so small that 

 they float for a long time in the air. They become coated by ab- 

 sorption with condensed layers of gas, which by heating in the air- 

 thermometer are partially liberated. The value of the coefficient 

 of tension thereby rises too high. But if the gas is at rest for some 

 time, these particles settle down and the air is again pure. 



If this explanation is correct, it must be possible by filtering the 

 air to get at once the normal coefficient of tension. Hence, after 

 passing the gas over the heated platinum through potash and sul- 

 phuric acid, I passed it through a layer of wool freed from fat, 

 15 centim. in length, which was so closely pressed that an excess of 

 20 centim. was necessary to drive the air through. After twelve 

 hours the value 3670 was obtained, by which the explanation is 

 confirmed. — Wiedemann's Annalen, No. 7, 1888. 



ON FREEZING MIXTURES MADE WITH SOLID CARBONIC ACID. 

 BY MM. CAILLETET AND E. COLARDEAU. 



In a recent Note (Journal de Physih, vol. vii. p. 286) we gave 

 the results of the comparison of various thermometric apparatus, 

 and showed that they held to a temperature below — 100°. 



The agreement in the indications of these instruments has led us to 

 use the most sensitive of our therm oelectrical pincettes, graduated 

 by direct comparison with the hydrogen-thermometer, to investigate 

 the temperature of solid carbonic acid, either alone or mixed with 

 various liquids. 



