500 



during the interval of the experiment to the equivalent quantity for 

 the primary vessel 



II. To deduce from the corrected change of level in the primary 

 vessel the relative density of Ozone and oxygen 



In these formulae 



a is the barometric pressure in terms of the sulphuric acid in 

 the U-tubes. 



H, the length of a tube of the same diameter as the TJ-tube of 

 the primary vessel, and whose capacity is equal to that of the 

 same vessel measured to the mean level of the acid in the TJ- 

 tube. 



H,, the same quantity for the auxiliary vessel. 



5a? p one-half of the change in the difference of levels in the TJ- 

 tube of auxiliary vessel. 



Ix, the corresponding quantity for the primary vessel. 



lx n , half the observed change in the primary vessel corrected 

 by the quantity <5#. 



m, the ratio of the weights of oxygen and Ozone in the gaseous 

 mixture. 



e, the relative density of Ozone and oxygen. 



VI. " Contributions towards the History of the Phosphorus-, 

 Arsenic-, and Antimony-Bases." By A. W. HOFMANN, 

 Ph.D., LL.D., F.R.S. Received June 18, 1857. 



The facility with which the phosphorus-bases can be obtained by 

 the action of zincethyl upon terchloride of phosphorus, has induced 

 me to study the action of this agent upon the terchlorides of arsenic 

 and antimony. I have found that triethylarsine and triethylstibine, 

 hitherto obtainable only with difficulty, by submitting the alloys of 



