142 E. W. Morl&y — Amount of Moisture in a Gas. 



He gives no results for acid more concentrated than this; but 

 from a comparison of the results for more dilute acids, it is 

 difficult to believe that an acid containing half a molecule of 

 water and one molecule of the monohydrated acid would give 

 up to a liter of absolutely dry air as much as the twentieth of a 

 milligram of water at ordinary temperatures. 



And as to the evaporation of sulphur trioxide from sulphuric 

 acid: Dumas* passed 20 liters of air through pure sulphuric 

 acid, and into solution of barium chloride, which preserved 

 " une limpidite absolue." But if the loss of weight observed 

 by Mathesius was due to the escape of sulphur trioxide, Dumas 

 should have obtained not only a visible but a weighable pre- 

 cipitate. 



But while we may dismiss the idea that sulphur trioxide 

 escapes from sulphuric acid in drying tubes in ordinary condi- 

 tions in any such quantities as several decimilligrams an hour, 

 it was necessary for the determination of the absolute amount 

 of moisture left unabsorbed by sulphuric acid that the amount 

 of sulphur trioxide volatilized should be accurately determined. 

 For this purpose I made several experiments. In one of them, 

 a wash bottle and a Winkler's absorption tube were filled with 

 pure sulphuric acid. This acid I distilled from a pure acid, re- 

 jecting the first and the last fifth. Its specific gravity at 22° 

 and at 16'8° C, compaied with water at 4°, weights being re- 

 duced to a vacuum, and the thermometer being corrected for 

 error of zero point, was found to be 1'8344 and l - 8394. A 

 current of air was aspirated through a gas-meter, through the 

 wash bottle of acid, through the absorption tube with acid, 

 through an empty tube two meters long, through a plug of 

 glass wool, and through an absorption tube with pure water. 

 The acid in the absorption tube occupied about two meters and 

 a half ; the water in the other absorption tube occupied about 

 a meter. The parts of the apparatus were fused together. 

 When 6800 liters had passed, not too rapidly, the sulphuric 

 acid in the water was determined as barium sulphate, and found 

 to. be 3"1 milligrams. In a second experiment at a somewhat 

 lower temperature, "7900 liters were passed and 2*5 milligrams 

 of acid were found in the second absorption tube. Several ex- 

 periments were made in which air passed, at the rate of two 

 liters an hour, into a solution of barium chloride ; in which ex- 

 periments neither myself nor Dr. Spenzer, my assistant, could 

 detect any trace of a precipitate till the third day. 



With the degree of approximation thus far obtained, there- 

 fore, we may conclude that a liter of air passed through sul- 

 phuric acid of the specific gravity of 1*84 will take up some- 

 thing like the two thousandth or three thousandth part of a 

 milligram of sulphur trioxide at ordinary temperatures. 



* Ann. China. Phys., 3d Series, vol. viii, p. 204. 



