Ohfervatiovs o?i Maddcnng, I71 



The briffhtnefs and fixity of the colours obtained fiom mad- 

 dcring depend not only on the procefs, but alio on the Ikte 

 and purity of the water as well as of the madder. It is 

 therefore abfolutelv nccefiary to avoid or to render inadtive 

 every acid, alkaline or faline fubftance that may be contained 

 in the water, or in the madder iifclf. I have (liown that, by 

 adding carbonate of lime, (pounded chalk,) madder which I 

 fufpc<Hed to conmin gallic ?.c\d. was corrctted ; but that mv 

 friend Ctiarles Bcrtholdi, ]irofelibr in the central fchool of the 

 Upper Rhine, afterwards found that it was fulphuric acid 

 united to magnelia. 



The important difcovery of tliis addition of chalk, which I 

 made twentv-five vcars ago, has given birth to many manu- 

 fad-iories, and improved all thofe eilahlillied near waters 

 which do not run over or hold in folution this earthy 

 fait, without which it is abfolulely impoffible to obtain, 

 beautiful and fixed madder colours. This chaik fince that 

 time has become a new objcftof commerce ; and as the price 

 is VLTV moderate, I have not yet determined the ju(i; propor- 

 tion to be employed : in general, I take one part for four, 

 five, or fix, of madder. 



In order to obtain the brighteft madder colours, it is not 

 fuffiuient to attend to the quality of the water and of the mad- 

 der : it is necelTary alfo to obfervc the degree of the heat of 

 the bath : a low temperature will check the altraclion of the 

 colouring parts, and prevent them from being extra6tcd, 

 while one too high will favour the adhefion of the vcllow 

 particles of the madder, which obiVure, and tarnidi the (hades 

 intended to be produced 'l"he only colour which gains by 

 jncrcalincj the heat is black. I have alwavs obfcrvcd, that 

 on withdrawing the fire from below the boilers, when the 

 liand can no longer be held in the acjueous vehicle which 

 they contain, if the niaddering be tlieii contuuicd f()r two or 

 three hours, the mod f;itisfi6tory rcfulls will be obtained, as 

 the furnace Hill retain'^ a I'uftieient quantity of heat to main- 

 tain the vehicle at the fame temperature, cfpecially when, ac- 

 cording to cuftom, large boilers are employed. P>elides, it 

 wo'.ild be very diiHcult to [\\ a determinate degree of heal by 

 the thermometer when the furnaces are large. 



'i'he vellow parts of the madder as well as of other colour- 

 ing fubttances are, it is probable, nothing elle than the co- 

 louring parts lli^ifclvts combined with oxvgen. The pro- 

 «lurt of this combination, by acquiring gicaier folubilily, 

 fuffers itlclf with more difliciiltv to he taken away by clearintr, 

 if the heat has not been properly regulated during the procefs 

 of dyeing. 1 have ofleu obfcived that madder and other co- 



iuurinj; 



