COMPAUISON OF DIFFERENT KINDS OF ALUM. ggj 



By these experiments we find, that the five alums act ge-NNo difference 

 nerally in the same maoner on woollens, that they produce ^JJ ^^^^^Jj, ^ * 

 some (lifterencc in cotton, and that their effects differ greatly great on sUk, 

 on silk. But these alums contain precisely the same propor- 

 tions of the same principles, and differ only by t-s^o-tt of sul- 

 phate of iron: we are therefore obliged to conclude, that the 

 differences mentioned must be ascribed to this sulphate. 



The following are the experiments we made to establish 

 this fact. 



Art. II. Alums of Rome, Boutier, Liege^ Javelle, and CU" 

 raudau, in their common state, compared with the same alums 

 pur'ificd. 



After having freed these five alums from all the iron that The difference* 

 existed in thep, we made comparative trials with them si^lplfate of ^ 

 thus purified, and with Roman alum and the alums of French iron. 

 manufacture. 



We first employed prussiate of potash to precipitate their 

 iron ; but as this method was slow and expensive, we substi- 

 tuted the more simple and -well-known process of dissolving 

 the alum rn boiling water, and washing the pulvcriform crys- 

 tals in cold water. In this way we obtained the complete 

 separation of all the sulphate of iron iVoTn our most impure 

 alum, which then was no longer perceptibly affected by prus^- 

 siate of potash, even after several days exposure to the air. 

 So complete a purification however is altogether unnecessary 

 for the purposes of the arts. 



Wool. 



Exp. \6. Weld yellow. 



J7- Cochineal. 



18. Madder. 



19. '• •• ••Kermes, 



Thread. 

 20. -....Weld. 



Cotton thread. 



21. Weld, 



22. Madder. 



Exp. 23. Sumach. 



Calicoes. 

 2i.......Weid, 



25. Madder. 



26. Sumach, 



Silks. 



27. Weld. 



28. •«.» ••Cochineal, 

 29. .... .. i'ustiic. 



Table of ejfpf. 



rinjents. 



v^'nk 



