214 ANNUAL OF SCIENTIFIC DISCOVERY. 



which is on a par with the fact observed by Stcnhouse, that the decolorizing 

 power of wood-charcoal is considerably increased by precipitating alumina 

 upon it. 



According to the author, mordants act by producing insoluble colors (lakes). 

 Their behavior towards coloring matters in solution must be ascribed to 

 chemical affinity, with which, however, the fibres themselves have nothing 

 to do. 



SULPHUR-BLEACHING. 



Schoenbein, of Basle, has discovered some exceedingly interesting facts 

 relative to this process. The fumes of burning sulphur, as is well known, 

 consist of sulphurous acid, and arc extensively employed, especially in 

 bleaching straw hats. The moistened straw, exposed for a time to the action 

 of the fumes, acquires the desired whiteness. Chemical lecturers are in the 

 habit of illustrating this decolorizing power by immersing a flower, as, for 

 example, a red rose, in sulphurous acid gas, or its solution in water. The 

 color is discharged in a short time. Schoenbein has found that the bleach- 

 ing holds good only for a certain medium range of temperature. A rose 

 thus bleached has its color restored if subjected to the temperature of two 

 hundred and twelve degrees, as may be conveniently done by holding it in 

 a stream of vapor from boiling water. On cooling to the ordinary tempera- 

 ture, it appears white again, and its color may be thus alternately restored 

 and discharged for a great number of times. Schoenbein has also found 

 that water colored by infusion of a red dahlia, and then bleached by sulphur- 

 ous acid, yields, by cooling, an ice which at twenty degrees below zero is 

 visibly red, but on wanning becomes colorless again. 



MAUVE DYE. 



This exquisitely beautiful dye for silks is prepared by talcing equivalent 

 proportions of sulphate of aniline and bichromate of potash, dissolving them 

 in water, mixing, and allowing them to stand for several hours. The whole 

 is then thrown upon a filter, and the black precipitate which has formed is 

 washed and dried. This black substance is then digested in coal-tar naphtha, 

 to extract a brown, resinous substance; and finally digested with alcohol, to 

 dissolve out the coloring matter, which is left behind, on distilling off the 

 spirit, as a coppery, friable mass. This is the dyeing agent producing all the 

 charming varieties of purples known by the name mauve, which, as it appears 

 to us, somewhat inappropriately, has been given to this color. The partic- 

 ularity of these purples consists in the peculiar blending of the red and blue 

 of which they are constituted. These hues admit of almost infinite variation ; 

 consequently, we may have many varieties of red mauve, and as many of 

 blue mauve, and any depth of tint can be secured. The permanence of these 

 hitherto fugitive combinations is their strongest recommendation. 



NEW BLACK DYE. 



A new black dye has been recently discovered in Algeria, which is the 

 subject of considerable interest among French chemists and manufacturers 

 at the present time. The discovery has been made by M. Muratcre, and is a 

 vegetable substance gathered from a tree which grows in immense profusion 

 all over the colony. It is destined, according to the report made upon its 



