188 PROCEEDINGS OF THE AMERICAN ACADEMY 



hydrogen is replaced by fluorine. Nor do we intend to continue our 

 experiments on acetic acid and benzol, as Paterno has announced that 

 he is at work on the fluorine derivatives of both these substances. 

 We wish, however, to reserve for our future study the action of 

 chromic superfluoride on all other organic substances. 



The remainder of the paper consists of the detailed account of our 

 experimental work. 



Action of Chromic Swperjiuoride on Benzoic Acid. 



The chromic superfluoride was made by the action of 180 gr. of 

 fuming sulphuric acid on 60 gr. of potassic dichromate and 100 gr. of 

 calcic fluoride, both of which must be perfectly dry. If the fuming 

 sulphuric acid is very strong, it should be diluted with ordinary strong 

 sulphuric acid, as, if this precaution is neglected, the action is so vio- 

 lent that it cannot be controlled, a large amount of the superfluoride 

 is wasted, and in extreme cases the cover may be blown off the lead 

 retort. The lead retort used was of the cylindrical form figured in 

 most text-books for making the aqueous solution of hydrofluoric acid; 

 the fuming sulphuric acid was flrst introduced, the fluor-spar and 

 potassic dichromate previously thoroughly mixed were then added, 

 and stirred in with an iron rod, the cover put on, and the reaction 

 started by a gentle heat. As soon as faint white fumes appear at the 

 exit tube, the latnp should be removed, and, after the first violent evolu- 

 tion of gas has slackened, the action can be made to proceed smoothly 

 by a gentle heat, although it is hard to avoid occasional rushes of gas. 

 It is hardly necessary to say that the work should be carried on under 

 a good hood, and the hands protected by india-rubber gloves. After 

 the process is finished, the retort should be emptied before it has become 

 cold, as after the residue has hardened its removal is both diflicult and 

 tedious. 



The chromic superfluoride obtained in this way is not free from 

 hydrofluoric acid, to ^udge from the white fumes which were observed 

 mixed with the dark red heavy vapor; but it was pure enough for our 

 purpose, and was allowed to act directly on the solid benzoic acid, 

 which was spread in a layer rather less than a centimeter thick over 

 the bottom of a platinum dish, or on its cover ; for this purpose the 

 lead pipe, which formed the exit tube of the retort, was brought down 

 so that it nearly touched the surface of the acid. Absolute contact must 

 be avoided, as in tliis case the tube soon becomes stopped u|) with the 

 fused product. With a rapid stream of the superfluoride the action 



