396 Intelligence and Miscellaneous Articles. 



A plate of red glass, of 0*08 of an inch thick, entirely deprived the 

 light of phosphorescent power, whereas a similar piece of violet glass 

 acted nearlj^ like colourless glass, though in some cases the effect 

 appeared more strongly marked. YelloM'ish-green glass entirely de- 

 prived electric light which traversed it of its phosphorescent power. 

 It appears therefore that colourless glass deprives luminous rays of 

 the o-reater part of their phosphorescent power, and that the quan- 

 tity of this power which is taken away by the violet glass, is gradu- 

 ally increased as blue, yellow, and orange glasses are used, the last 

 mentioned entirely destroying the phosphorescent power. 



The following experiment also confirms the effect which has been 

 described with screens of white glass placed in the passage of the 

 lio-ht : recently calcined oyster-shells were exposed to the light of a 

 bil; of phosphorus burning in a bottle filled with oxygen gas. The 

 light emitted was most intense, and yet the phosphorescence which 

 it occasioned was slightly so. 



To conclude, it is evident that electric light, besides chemical and 

 calorific luminous properties, also possesses phosphorescent power, 

 which is taken from it partly or almost totally by different sub- 

 stances, which allow the light to pass through them without any sen- 

 sible diminution. — L'Institut, No. 270. 



ON THE PREPAR.'VTION OF SELENIC ACID. BY HENRY ROSE. 



M. Mitscherlich's process for preparing this acid with selenium or 

 a metallic seleniuret consists, as is well known, in fusing them with 

 nitrate of potash or soda. A ccording to Berzelius, it may be obtained 

 with selenious acid by converting it into selenite of potash, mixing 

 the solution of this salt with a little caustic potash, and passing chlo- 

 rine "-as throuo-h the solution to complete saturation : by this process 

 there^is obtained a mixture of chloride of potassium and seleniate of 

 potash. These two methods yield selenic acid combined with an 

 alkali, and it is difficult and tedious to separate and combine it with 

 certain other bases. 



In his first experiments with chlorine gas upon the metallic sele- 

 niurets of the Hartz, the solution obtained by mixing the voltatile 

 chloride of selenium Avith water, through which excess of chlorine was 

 passed, yielded no precipitate of selenium on the addition of a solu- 

 tion of an alkaline sulphite ; and this re-agent produced no precipi- 

 tate of selenium till hydrochloric acid was added and boiled with it 

 for a long time. The selenium evidently existed in the liquor in the 

 state of selenic acid, which was not reduced to that of selenium by 

 the alkaline sulphites, till the moment at which the hydrochloric 

 acid converted it into selenious acid. 



If then it be desired to prepare free selenic acid, the best process 

 is that of passing chlorine gas through a solution of chloride of sele- 

 nium or selenious acid. It is then obtained, mixed only with hy- 

 drochloric acid, which when dilute and cold, does not reduce the se- 

 lenic acid. . 1 r 



The best method of producing selenic acid immediately from sele- 

 nium is the following : reduce the selenium to coarse powder, put it 



