MORDANTS,

293

made of copper, and upon which the design is engraved: as regards chintz andlarge patterns, these are obtained by what is termed block printing, woodenblocks being used containing the engravings of the patterns. Immediatelyafter the cloth leaves the printing-machine it is dried by passing overmetal plates heated bysteam. By this operation acetic acid is volatilised,and a basic salt remains on the cloth. When block-printing has beenresorted to, the drying takes place in a drying-room at a lower temperaturethan that just given, and consequently less acetic acid is volatilised.The fixation of the mordant is effe&ed by two distindt operations, one ofwhich, viz., the “ ageing,” has been described already. We add here thefollowing particulars as regards the time required for the mordanted cloth toremain in the ageing room : for chocolates and browns, 72 hours ; for purplesand browns (another shade), 60 hours ; for blacks and reds (if together)*.48 hours ; for pinks and reds, when not occurring along with other mordants,from 6 to 20 hours. It should be observed here, also, that proper ventilationmust be kept up in the ageing rooms, since the presence of the vapours ofacetic acid is injurious to the mordants, and since the admission of cold air tothese rooms would condense the steam, and thereby spoil the goods : heatedair is required for keeping up the ventilation.

We may quote here in full the researches made by M. H. Schiffert with theview of ascertaining the nature of the aluminous compound remaining 011 thetissues after drying and ageing :—(i\ A piece of cotton, printed for foulards (akind of handkerchief used in France for head-covers by women), and mor-danted with acetate of alumina not containing any sulphate, was dried andsubmitted to the ageing process for several days ; the cloth was next placed ina glass retort, and, after water and sulphuric acid had been added, distillationwas performed. The result of this operation was that a perfectly neutralliquid was obtained, not containing even the slightest trace of acetic acid,which latter would have appeared if a basic acetate had remained on the clothinstead of hydrated alumina. (2). A piece of calico mordanted with alum,three-fourths of the sulphuric acid of which had been replaced by acetic acidfrom acetate of lead, was similarly dried and aged, and on being treated withcold water yielded sulphate of alumina. It hence follows that the acetate oflead had divided its a&ion between the sulphates of alumina and potassa,both of which were present in the alum, while a portion of the alum had beenleft unadted upon. The tissue yielded, after being previously washed withwater, on distillation with dilute sulphuric acid, not a trace of acetic acid.After washing, and next boiling with carbonate of soda, the resulting liquiddid not contain sulphuric acid, which should have been present had thereremained a subsulphate of alumina. Treated with hydrochloric acid,aided by heat, a large amount of alumina was obtained, precipitable byammonia. (3). A piece of calico mordanted for ordinary red, dried, and agedfor the usual length of time, did not on assay yield any acetic acid ; treatedwith cold water it yielded a solution which became turbid by ebullition,throwing down a basic sulphate of alumina which can again serve as a mor-dant by being heated to 70° C. When a piece of this tissue was well andthoroughly washed with cold water it only retained hydrate of alumina, allthe sulphuric acid being removed. The result of these experiments is, therefore,that fabrics mordanted with acetate of alumina do not retain, after dryingand ageing, any acetic acid at all, not even in the state of basic acetate.