162 [June 19, 



earths, as also the phosphates, arseniates, and borates, are likewise 

 tolerably transparent, though saturated solutions of phosphoric and 

 arsenic acids exerted considerable absorbent power ; so also did those 

 of the alkalies, potash, and soda, possibly from the presence of a 

 trace of some foreign colouring matter, as those liquids had an ex- 

 tremely faint greenish tinge. 



The soluble fluorides, as well as the chlorides and bromides of the 

 metals of the alkalies and alkaline earths, are freely diactinic, but the 

 iodides are much less so, and exhibit certain peculiarities. All the 

 organic acids and their salts which were tried by the author exerted a 

 marked absorptive action upon the more refrangible rays. Amongst 

 those subjected to experiment were the oxalates, tartrates, acetates, 

 and citrates, those mentioned first in order having the greatest ab- 

 sorptive action. It is, however, much more difficult to obtain or- 

 ganic compounds in a state of purity sufficient to furnish trustworthy 

 results, than is the case with the salts of the inorganic acids. The 

 author, therefore, expresses himself with more reserve upon some of 

 these organic bodies, particularly the acetates, than in other cases. 

 The different varieties of sugar are freely diactinic. 



Amongst the salts of inorganic acids, the nitrates are the most 

 remarkable for their power of arresting the chemical rays. A solu- 

 tion of each of these salts, in all the instances tried, cut off all the 

 more refrangible rays, and reduced the spectrum to less than a sixth 

 of its ordinary length. The chlorates, however, do 'not participate 

 in this absorptive power to nearly the same extent. 



Although the sulphates, as a class, are largely diactinic, the sul- 

 phites are much less so ; and the hyposulphites cut off about three- 

 fourths of the length of the spectrum, leaving only the less re- 

 frangible portion. 



Of eighteen different liquids tried by the author, two only can be 

 regarded as tolerably diactinic, viz. water, which is eminently so, 

 and absolute alcohol, which, however, exhibits a considerable falling 

 off. The liquids which follow are mentioned in the order of their 

 chemical transparency, those most transparent being mentioned first : 

 Dutch liquid, chloroform, ether; then benzol and distilled gly- 

 cerin, which differ but little ; then fousel oil, wood-spirit, and oxalic 

 ether, which are also nearly alike ; acetic acid, oil of turpentine, 

 glycol, carbolic acid, liquid paraffin, boiling at 360 F., and bisul- 



