﻿Molecular Dimensions of Sulphur Dioxide. n09 



Preparation and Purification of the Sulphur Dioxide. 



The sulphur dioxide was generated by the action of dilute 

 sulphuric acid on sodium sulphite. It was dried by being 

 passed through several wash bottles containing concentrated 

 sulphuric acid, and then solidified in a U-tube surrounded by 

 liquid air. The U-tube was then cut off from the generating 

 apparatus, and all permanent gases removed by means of a 

 pump. The gas was made to evaporate by removing the 

 liquid air, and Samples were collected over mercury. The. 

 chief difficulty in using this gas is to dry it sufficiently well 

 that the motion of the pellet of mercury in the fall tube shall 

 be smooth. It is difficult because sulphur dioxide boils at 

 — 10° C, and at this temperature water has a small vapour- 

 pressure. It was finally purified and dried in the following- 

 way, before introduction into the viscometer : — The gas was 

 solidified in a tube maintained at — 80° C. by means of a 

 mixture of solid carbon dioxide and alcohol, and all per- 

 manent gases and possible traces of carbon dioxide removed 

 by means of a Toepler pump. Sufficient alcohol was then 

 added to the carbon dioxide mixture to raise the temperature 

 to — 60° G. At this temperature water has a negligible 

 vapour-pressure, while sulphur dioxide is liquid and has an 

 appreciable vapour-pressure. This enabled successive small 

 quantities of the dry gas to be pumped off and introduced 

 into the viscometer, which was previously exhausted, until 

 the pressure therein was atmospheric. 



Experimental Results. 

 Table I. 



Each time recorded in this table is the mean of four observations in each 

 direction for the whole pellet, and of three when the pellet is divided into two 

 segments. The letters in parentheses indicate the order in which observations. 

 were made. 





Time of fall (sees.). 







Time at 



Temp, 

 (deg. C). 







Capillary 

 correction. 



C^rwrfrntPfl 





Whole 



Two 



time 



18°-0C. 



ioo°-oc. 





pellet. 



segments. 



0*0- 



(0- 









(a) 17-72 



~ 76T6~ 



79-67 



00422 



72-95 



7303 



(b) 17-80 



76-48 



80-38 



00463 



72-95 



7301 





(c) 17-85 



76-82 



81-00 



00491 



73-05 



73-09 





(/) 17-38 



76-40 



80-37 



00471 



72-80 

 Mean 



72 97 

 ...7303 





(d) 100-0 



97-10 



99-32 



0021 9 



94-97 





94-97 



(e) 99-96 



97-13 



99-37 



0220 



94-99 





9500 













Mean 



...9499 



