upon the Vrcpara'lon of Indigo. 259 



Boichot designs very veil after the old masters ; he prefers 

 the Florentine school. Naiidel is one of those artists who 

 unites in one person all the qualities of a travelling painter. 

 He has accompanied me for these five years past in my tra- 

 vels. The 500 dcs!q;n?, which are the fruit of these travels, 

 will proive the accuracv of my opinion. 



I may have still omitted some very distinguished artists, 

 who may have been fortiotttn by M. fiorillo also ; and as 

 I have trusted to mv mtmory alone, my only desire has beeu 

 that it should not deceive me too ofien. 



XLIII. Upon the Preparation of Indigo for oltulning Blue 

 Colours for printing Calicvc::;*. 



JS'L. IlAUssMANjin a letter addressed to M.Bcrthollet, gives 

 an account of the manner in which the solution of indigo is 

 prepared, bv means of an alkaline solution of red arsenjc, for 

 the use of calico printers. 



He merely makes a caustic alkaline solution of red arsenic, 

 to which he adds, while it is still boiling, a sufficient quan- 

 tity of indigo bruised, in order to obtain a very deep shade ; 

 which it IS still easy to render more or less intense, as the 

 object may require, by diluting the solution of indigo with a 

 weak lev of caustic potash, which is preferable to pure water, 

 because it relards a little the absorption ol the oxygen of 'he 

 atmosphere, and con5ec[uently retards the regenerauon of the 

 indigo. The beauty of the blue in the stuffs requires that this 

 regeneration should not be too sudden or too Lirdy. The 

 too slow absorption, proceeding from a too great excess of 

 caustic alkali, should be avoided in the blue for pencilling 

 with, as well as in the sone blues, which advantage we procure 

 by passing the stuffs printed with bruised indigo, mixed with 

 a gummy solution of sulphate of iron, alternately through 

 vats of caustic potash, sulphate of iron oxidated at the wzV/i- 

 muiTiy and finally through a vat 'acidulated by the sulphuric 

 or muriatic acids. 



* Froia A:\nalts dcs Am ct ^fcn^f'>lCliirei. Mav IfCC; p. 181. 



R 3 "^ On 



