•COMPARISON OF DIFFERENT KINDS OF ALUM. 277 



ration; and he concluded, that any ttlum,' free from iron, 

 would be as good for use as the Roman. To place this be- 

 yond question however, it would be proper to make compa- 

 rative experiments with them in dyeing. 



Encouraged by this some skilful manufacturers farther 

 improved the produce of their works, and supplied the shops 

 with alum, that wantM only a diiierent name and appear- 

 ance to rival the Roman. 



But the predilection for Roman alum was soon abused; FactitJoits 

 and considerable quantities of the alums of Liege a"^ ""a^rforR^ ^"^ 

 Javelle, to which all the outward appearance of that of man. 

 Totfa had been given, were sold. Most of the dyers and 

 manufacturers however, wlio at first had been imposed on 

 by this appearance, were induced afterward to be only so 

 much the more eager for the true Roman alum : for it was 

 much more easy to deceive tlum to convince them. 



Sucli was the state of our knowledge repecting alum, Piize offered by 



when the Society of Encourasjement, ever animated with a ^^^ Society of 

 -t • n ' • ' r. 1 Encouraae- 



desire ol givmgour own manutactures a great preponderance ment. 



over those of foreign countries, thought fit to oifer a prize 

 for the means of giving our alums all the properties of that 

 of Rome. The society having employed Messrs. Thenard Directed a 

 and Roard, to compare the Roman alum with that of French examl'^'tionJi 

 manufacture", in order to ascertain the difference both of of F'enL-haoSf 

 their nature and effects; these gentlemen, after having ac- ^"^^^^^^ '^ ^""^1 

 quainted the society with the results of their inquiry, sub- 

 mitted them to the Institute, before whom they laid the 

 numerous experiments they had made to solve the question. 

 They were very careful to, obtain the French alums in the Their prccau- 

 state in which they are commonly sold, and accordingly ^'°"*' 

 procured them themselves either from the manufacturers or 

 from the warehouses, taking at a venture a great variety of 

 cr^^stals from among considerable heapa. 



It was of particular importance likewise, that they should 

 procure unmixed Roman alum. Accordingly they applied 

 to Mr. Schlumberger, their colleague, who has the care of 



the warehouse at Paris on account of the proprietors, and to 



\. v> ■ ' 

 * Messrs. Thenai a and Roard say nothing of the English alum, though 

 it appears from Vauqudiu's paper, that the French consumers give it a' 

 decided preference over any made in Fri\nce. T. 

 . 't; ^,,,,. whom 



