employed in tJie Art of Dyeing. 1S3 



attributed to the separation oT the acidulated sulphate of 

 potass, 'this being carried off with the uncombined mordant 

 in drving. 



CHAP. IV. 

 Art. 1. — Of the Scarlet Colour. 

 Scarlet is that bright and sliining colour which is pro- 

 duced in wool bv treating it with tartar, cocliineal, and a 

 highly oxidized solution oi" tin. Bctore the discovery of 

 this method, for which we are entirely indebted to Dreb- 

 bcl, those colours were called scarlet which are produced 

 in woollen stuffs by kernics or cochineal, when alum and 

 tartar are employed as mordants. These processes ibr ob- 

 taining this colour have lonsr been known in the dyeing 

 houses, yet no theoretic investigations have been made into 

 the phajnomena which take place when a solution of tin is 

 used with cream of tartar and cochineal. Dr. Bancroft at- 

 tempted to explain what passes in the f(jrmHtion of this co- 

 lour; but as his opinion does not a])pear to be founded on 

 any experiments, we considered the question as not at all 

 determined by his labours. We propose, therefore, in this 

 fourth chapter, to determine the clieniical up.ture of the, 

 combination formed upon wool by cochineal, tartar, and a 

 solution of tin, and to make known the result of our in- 

 quiries upon the colour of scarlet. 



Art. 2. — Exnmi?iaiinn of the Precipitate formed by the 

 Solution of Tin, and the acidi/hi/ed Tart rite of Potass. ■ 



All the substances employed by us in our experiments 

 were perfectly pure, and we constantly made use of glass 

 vessels and distilled water. Eighty grammes of acidulated 

 tartrite of potass dissolved in three kilogrammes, and five 

 hectogrammes* of distilled water, were macerated for two 

 hours, ai 100 degrees (i2i2 F.) of heat, with one hundred 

 and twenty-five grains of a solution of tin. The precipitate 

 which we obtained was waslied several tinies, and distilled 

 in a small curved retort, the beak of which being ])lunged 

 into lime water, there was disengaged a sensible quantity 

 of carbonic acid. Proper re-ageiils indicated in other por^ 

 lions of it the presence of a great deal of tin and nun-iatic 

 acid, 'fhus the cream of tartar and solution of tin arc de- 

 composed, and produce a precipitate, consisting of tar- 

 taroi)s acid, and a great quantity of muriatic acid and 

 till. The mother-water contains tartrite of potass, aci- 

 dulated tartrite, very acid muriate of tin, and a considerable 



* Al'out scveii pi:it«. 



M 4 portion 



