278 



COMPARISON OF DIFFERENT KINDS OF ALUM. 



Plan of their 

 proceedings. 



•♦ 



Alums com- 

 j)dred. 



Analysis. 



For the sul- 

 pliuric acid. 



whom all the Roman alum is directly sent. Accordingly lie 

 had a great number of cask^ opened, that they mi^ht exa- 

 mine the external appearance, figure, and colour of the 

 crystals; and from each they took what they judged proper, 

 to make up in the whole the weight of 30 kilogrammes 

 [about 67lbs.] Tlie superiority of the Roman alum over all 

 other kinds met with in the shops being the object of the dis- 

 pute between the chemists and manufacturers, Messrs. 

 Thenard and Roard conceived, that to decide it an analysis 

 on a large scale alone would be insufficient ; and that it was 

 particularly necessary, to make numerous and very accurate 

 experiments with the best known colouring drugs on the 

 fabrics most iu use : and they conceived, that if, from the 

 whole of the facts, they could discover any necessary and 

 direct connexion between the results of the analysis and the 

 practical experiments, between the principles found by the 

 one and the effects obtained by the other, all the difficulties 

 would be elucidated, all doubts removed, and theory con- 

 joined with experience would lead them to a complete solu- 

 lution of the question. 



The French alums subjected to their researches corapa- 

 rative'y with the Roman were those of Bouvier, Liege, 

 Javelle, and Curaudau. 



Before they compared the effects of these various alums in 

 dyeing, their first care was to subject them to all the ana- 

 lytical trials already made by the chemists we have men- 

 tioned : thus at the same time they determined the propor- 

 tions of acid, alumine, potash, and water, and observed, as 

 Bergman, Vauquelin, and Chaptal had done before them, 

 the dangerous influence of iron. The experiments they 

 made on this subject constitute the first part of their memoir. 



Part I. 



Avalysis of Afums, 



Exp, 1. To determine the proportions of sulphuric acid, 

 they dissolved in l6 litres [or wine quarts] of water 489 gr. 

 [15 oz.,6dr. troy] of each of the preceding alums entirely 

 freed from the dust that coiners the surface of some of -them*. 



♦ The rosy du&t on the Roman alum yielded on analysis saturated 

 sulphate of alumine and ^mta&lt^ silex^ and oxide of iron. 



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