Profs. Andrews and Tait on the Density of Ozone. 147 



described in the commnnication already referred to. It was easy to 

 measure with certainty a change of pressure amounting to g^th 

 of the wliole ; but on account of the ordinary fluctuations of atmo- 

 spheric pressure between two consecutive observations of the primary 

 and auxiliary vessels, it was rarely possible to work to this degree of 

 accuracy. 



The experimental data have not yet been completely reduced, and 

 some slight corrections have yet to be investigated ; but the general 

 result of the inquirj', which has been a very protracted one, gives — 

 on the assumption that ozone is oxygen in an allotropic condition — 

 for its density as compared with that of oxygen, nearly the ratio of 

 4 to 1. 



The following approximate formulae were employed in the reduc- 

 tion of the experiments. They are sufficiently exact for the purpose 

 of calculation on account of the smallness of the quantities observed. 



I. To reduce the change of level observed in the auxiliary vessel 

 during the interval of the experiment to the equivalent quantity for 

 the primary vessel — 



(!4)-=(^fl>- 



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

 vessel the relative density of ozone and oxygen — 



e-1 /2 . IN. 



In these formulae 



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



the U-tubcs. 

 II, the length of a tube of the same diameter as the U-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 



U-tube. 

 II,, the same quantity for the auxiliary vessel. 

 cXf, one-half of the change in the difference of levels in the 



U-tube of auxiliary vessel. 

 hx, the corresponding quantity for the primary vessel. 

 Ixii, half the observed change in the primary vessel corrected 



by the quantity dx. 

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



mixture. 

 e, the relative density of ozone and oxygen. 



" Contributions towards the History of the Phosphorus-, Arsenic-, 

 and Antimony-Bases." By A. W. Ilofmann, Ph.D., LL.I)., F.R.S. 



The facility with which the j)hosphorus-bascs can be obtained by 

 the action of zincctbyle u])on terchloride of f)liospborus, has induced 

 me to study the action of this agent upon the terchloridea of arseuic 



