Dr. Andrews on the Constitution and Properties of Ozone. 455 



indicative and peculiar ? One of these bodies, from the analysis 

 hitherto made, would seem to have a formula not very different from 

 the following, viz. C^-^H--N- 0^ + P, and crystalhzes in hexagonal 

 prisms, passing by the ordinary replacement planes to the acute 

 rhombohedron and other forms, all apparently derived from the 

 rhombohedric system; some of these crystalline forms are very strange 

 and unusual. This substance possesses " double absorption" in a 

 very evident degree, and when examined by vertically plane polar- 

 ized light, the hexahedral prisms are all obstructive of the polarized 

 beam when the length of the prisms lies parallel to the plane of the 

 incident ray; in this position they appear dark sienna-brown in 

 colour ; when the long axis of the prisms lies perpendicular to the 

 plane of primitive polarization the crystals transmit a lemon-yellow 

 tint, passing through greenish yellow to sherry-brown. 



The other substance aj)pears to be the sulphate of iodo-strychnine 

 and has a decidedly metallic green reflexion, crystallizes in stellate 

 aggregations of prisms, brilliantly green by reflected light, but 

 having a deep blood-colour by transmission ; these also possess double 

 absorption and are very peculiar, as a slight increase in thickness 

 renders them wholly impervious to light. 



When these matters have been more carefully worked out, I hope 

 to have the pleasure of communicating the results to the Society: in 

 the mean time the present notice will be sufficient for the object in 

 view. , 



1 remain, my dear Sir, 



Yours very truly. 

 Professor Stokes, F.R.S. W. Bird 'Herapath. 



" On the Constitution and Properties of Ozone." By Thomas 

 Andrews, M.D., F.R.S. 



The conflicting views which have so long existed as to the true 

 constitution of ozone, induced the author to undertake a careful in- 

 vestigation of the subject, particularly as he had reason to doubt the 

 accuracy of the only quantitative experiments which have yet been 

 made to elucidate this difficult question. According to the experi- 

 ments referred to, two substances have been confounded under the 

 name of ozone, one a compound body having the formula HO3, the 

 other an allotropic variety of oxygen. To ascertain whether, in con- 

 formity with this statement, ozone obtained in the electrolysis of 

 water contains hydrogen as a constituent, the author made two 

 series of experiments. In the first series, he followed nearly the 

 same method of investigation by which its compound nature is sup- 

 posed to have been established, but modified so as to avoid a source 

 of error, which, if neglected, vitiates altogether the results. Electro- 

 lytic oxygen, unless very great precautions be taken, is always ac- 

 companied by a small but appreciable quantity of carbonic acid, 

 which is liable to be partially absorbed by the potassa set free when 

 a neutral solution of iodide of potassium is decomposed by ozone. 

 By adding a little hydrochloric acid to the solution of iodide of 

 potassium before the commencement of each experiment, this error 

 may be avoided. 



