1836.] of the Wet-bulb Hygrometer. 425 



the readings which were considered as coincident, but, as before, there 

 was difficulty in keeping the dry thermometer stationary, 



Tab. X. — Depressions with Hydrogen gas. First Series. 



Tabular de- 

 Therm. Wet- Depres- Hygro- Tension pression in Ratio, 

 in air. bulb. sion. meter, centesimal. dry air. 



o o o d4* D 



1. Through steam pipe, 92.0 67.8 24.2 — ? 37.1 



2. Ditto, steam on, .. 160.0 83.2 76.8 — nearly dry. 81.5 .94 



3. Ditto, ditto, 137.0 76.4 60.6 — ditto. 65.3 .93 



4. Ditto, cold, 93.8 67.5 26.3 44? .17? 38.1 



The hydrogen of the gasometer in the first two experiments was 

 supposed to be dry, but it was found that it acquired moisture in pass- 

 ing through the pipes, which had been moistened by the distillation 

 of the hydrogen ; the amount of error was estimated by filling com- 

 mon air in, and finding how much its depression differed from the full 

 rate. The gas of 3, and 4 was passed out into a vessel containing 

 the hair hygrometer ; but still no great confidence was placed in the 

 series, and on two subsequent days fresh gas was prepared. 



Second Series. 



5. Protracted current of hydrogen gas,.. 85.4 60.0 25.4 



6. Common air treated exactly in the 



same manner, 90.6 59.0 31.6 = 29.1 at 85*4 



Ratio of 29*. 1 to 25°.4 as 1.00 to .87 



This was still unsatisfactory, as there was no mode of testing the 

 bygrometric state of the gas : I now therefore fitted the glass cham- 

 ber enclosing the hair hygrometer, (as in fig. 1) and took the follow- 

 ing readings after intervals of a day each. 



Calc. Maxim. Depress , 



in in Ratio. 



t V d h Hydrogen. Atm. air. d~-o 



7. Hydrogen , current, 87.8 60.5 27.3 8 29.5 34.8 .84 



8. Ditto, full draft, . . 88.0 59.7 28.3 5 29.8 34.9 .86 



9. Ditto, ditto 84.0 57.1 26.9 4 28.0 32.8 .85 



10. Ditto, ditto, 88.5 58.5 30.0 4 31.2 35.2 .88 



11. Common air 87.0 54.8 32.2 4? 33.5 34.4 



12. Ditto, 83.1 52.1 32.0 2 32.6 32.4 



Still a fourth series was thought necessary ; and in this all access 

 of moisture to the tubes being prevented by passing the gas over 

 sulphuric acid before it entered the gasometer, and leaving it for a 

 week to dry thoroughly, the hair hygrometer marked extreme siccity : 

 precaution was also taken to cool the wet-bulb with ice below the de- 

 pression point, before inserting it in the tube. 



Fourth Series, Hydrogen gas. 



t V d h. D (Z-7- D 



13. Full draft 86.7 58.5 28.2 34.2 .82 



14. Ditto 8f,.0 57.4 27.6 3X4 .83 



15. Ditto, 82.8 56.5 26.3 32.2 .81 



3 K 



