Aug., 1916
T H E JOURNAL OF I N D C S T R I A L A N D ENGINEERIXG CHEMISTRY
measured volume of liquid out of chamber H . Any excess liquid drawn up beyond line A B will be entrapped in either bore F , or in bore F a n d in chamber G. This excess is returnable by revolving t h e stopcock counter-clockwise through 90". The advantages of this pipette may be summarized as follows: I-It enables t h e operator t o automatically control a n exact measured volume of liquid drawn into t h e pipette. 2-It obviates t h e necessity of adjusting, maintaining a n d manipulating t h e exact volume of t h e liquid once it has passed t h e graduation mark, placed
Frs. 2 S e c t i o n at y - y
FIG.1
FIG.3 - S e c t i o n at x-x
where t h e stopcock meets t h e lower end of t h e valve of t h e pipette. 3-It permits t h e discharge of t h e exact measured volume of liquid from t h e pipette. is exceedingly easy t o manipulate. 4-It CHEMICAL LABORATORY, COMXERCIAL HIGH SCHOOL BROOKLYN, N E W YORK
THE DETERMINATION OF AIR, WATER VAPOR AND NITROUS OXIDE IN MIXTURES OF THESE THREE CONSTITUENTS1 By G. A. BURRELLA N D G. W. JONES Received M a y 19, 1916
The authors of this report had occasion recently to examine some samples of nitrous oxide (dentists' "laughing ,gas") for t h e presence of water vapor and Published with the permission of t h e Director of t h e Bureau of Mines.
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air. The mixture was first liquefied by means of liquid air, the air being then withdrawn with a Topler mercury pump, and measured. The residual gas was C., the nitrous subjected t o a temperature of -78' oxide being then withdrawn and measured. Finally t h e partial pressure of t h e water vapor was measured. This analysis is one of t h e many gas analyses t h a t can be performed by means of the apparatus shown in Fig. I. The apparatus is first exhausted of its air by means of a Topler mercury pump. and t h e sample of "laughing gas" is introduced at atmospheric pressure. Next t h e bulb A is immersed in a Dewar flask containing liquid air. After about I O min. t h e air is withdrawn from t h e mixture through t h e pump and measured. The vapor pressure of the air a t the temperature of liquid air is of course very high, and the air can be readily removed from the mixture. The vapor pressure of nitrous oxide is I mm. a t a temperature of -144. I " C.,l hence its pressure a t t h e temperature of liquid air is practically negligible. After t h e air has been removed and measured, the bulb A is immersed in a mixture of solid carbon FIG.I dioxide and acetone. This mixture Apparatus for t h e gives a temperature of -78 " C. Determination of Air, The bulb A is exposed t o this tem-Water Vapor a n d Niperature for about I O min., and of t r othe u s oThree x i d e i n Mixtures t h e nitrous oxide is withdrawn through t h e pump and measured. The normal boiling point of nitrous oxide is -88. 7 " C . 2 so i t can be readily removed from t h e mixture a t a C. On t h e other hand, t h e temperature of -78" vapor pressure of water is practically nil a t a temperature of -78" C. so t h a t it freezes and remains in t h e bulb A . After the nitrous oxide has been withdrawn and measured, t h e Dewar flask containing t h e solid carbon dioxide and acetone is removed from around t h e bulb A . The frozen water vapor then vaporizes and exerts its partial pressure on t h e mercury in the manometer tube C. This pressure is, of course, proportional t o the percentage of water vapor present. The results of the analysis of three samples of gas taken from t h e same t a n k follow: PERCENTAGE ANALYSESOF NITROUSOXIDE CONSTITUENT Sample I . . . . . . . . . . . . Sample 2 . . . . . . . . . . . . Sample 3 . . . . . . . . . . . .
AIR 2.0 2.1 2.0
NzO 95.9 95.6 96.2
Ha0 2.0 2.0 2.0
TOTAL 99.9 99.7 100.2
BUREAUO F MINES, WASHINGTON 1 G. A . Burrell and I. W. Robertson, "The Vapor Pressures of Sulliir Dioxide and Nitrous Oxide a t Temperatures below Their Normal Boiling Points," J . A m . Chem. SOC.,37 (1915), 269. 2 G. A. Burrell and I. W. Robertson, LOC. rit.
