£90 COMPARISON OF DIFFERENT KINDS OF ,AL13M. 



the aliiras of Bonvier and Cu:-audau, we can afiBrm, that the 



differences were very trifling, and onlv to be perceived by an 



expene^iced eye. 

 i-oW part of 5. The alum of Javelle, and that of Lie<>e in particular, 

 Loix luTurioixs. though not containing above a ihousaiKlth part of sulphate 



of iron, almost always produce duller and lesa brig;ht colours 



than those with purified or pure alums. 



Its effect great- ^. The effect of sulphate of iron is not the same on all 

 est on silk, s . ^ i -,.1 n i • ^^ • • 



. substances, and with all colounnj^ matters: it is very evi- 

 dent on silk ^vith \*eld and cochineal colours: it is a little 

 least on wool, less so on cotton, and it is much less on wool, with the same 

 substances. Wool appears to fix a less quantity of sulphate 

 of iron than cotton, atid particularly than silk ; for the co- 

 lours oil wool are less altered by ^V o^ t^'s sulphate than on 

 Little with silk by T^^i ^^^ ^^ all madder, archil, and kermes coloui*s, 

 *" kern*^'^'^^''' very large pro^wrtions of this substance are necessary to alter 



the shade, or^even to diminish its liveliness. 

 Every manu- ?• Every manufacturer of alum therefore, if he will, may 



facuirer "^^^7 ^bansre his most impure alum, by siuiple and not expensive 

 makeahimof '' . ....... 



the best qua- means, Hito an alum, that lu its application in all the aits, 



^'^y- to the most lively colours, and to substances the most sen- 



sible to the influence of sulphate of iron, shall possess all 

 the properties of the long: boasted Roman alum. 

 Remarks on Let US hope, that the importation of foreign alum into 



the French France, which amounted a few years ago to several millions 

 of livres, and which has already decreased in a considerable 

 degree, will soon cease entirely : that our alum manufactu- 

 rers, better acquainted with their real interest, will no longer 

 endeavour to distinguish their good.s by' that coloured coat- 

 ing, which has most frequently been the resource of fraud : 

 that their endeavours to furnish the shops with an alum con- 

 stantly pure will soon lead all our manufacturers to think no 

 more of Roman alum : and that ultimately our alum works, 

 obtaining deserved celebrity, will be greatly increased, ex- 

 tend their sale to foreign countries, and enrich France with 

 a consideijable branch of trade. 



IX. 



