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Aniline Blue (Re- colors The most sensitive)

Aniline blue re- colors. The most sensitive among these, for ults from various processes. The one most impure alcohol, is aniline purple (phenylommonly used at present is that of Girard and rosaniline). It appears that empyreumatic 'e Laire, made by heating fuchsine with fluid substances, aldehyde, the peculiar fusel oils due niline. The original process produced a blue to the substances used in the manufacture of the alcohol, affect the aniline colors when dis- | 2563. General Directions for the Use solved in such alcohols and boiled therewith. of Aniline Dyes. It is impossible to use The best test for the purity of an alcohol is to dissolve in it 1 per cent. of perfectly pure caustic potassa, and to heat the solution; it should only acquire a bright yellow color.

Another test is to dissolve 1 part of the aniline purple alluded to in 50 parts of the alcohol to be tested, and to heat the fluid for some time.

If, after half an hour's heating, no change is observed, the quality of the alcohol is good; but if the latter is not pure enough, the mixture soon becomes turbid, and assumes a red color. Another test is to make two solutions of the color of the same strength (1 in 50), one with alcohol of known purity, and the other any dye, successfully, without due regard to cleanliness. This is, perhaps, more particularly the case with the anilines. The slightest trace of a foreign substance will often materially alter the shade. Earthen or enameled vessels should be used whenever practicable.

Iron is generally to be avoided, if for no other reason than that it is difficult to say when it is really clean. Woolen and silken goods, before being dyed, should be thoroughly washed in soap and water, and then carefully rinsed in clean rain water. Cotton requires a previous mordanting before it can be dyed with anilines, as vegetable fibre possesses no with the suspected alcohol, and then compare affinity for the colors. The preparation genthe intensity and shade of the solutions. Al- crally consists in treatment by sumac, or dehyde is often present in alcohol, especially stannate of soda, and subsequently by sulif it has been purified by means of charcoal. phuric acid; special directions will be given 2560. To Test the Quality of Aniline in those cases requiring particular treatment. Colors. A good and practical way of testing Old fabrics which were dyed before, may be the merits of aniline colors is to have, and freed from color by previous boiling for an keep on hand, a standard and measure of com- hour in strong soapsuds. The spirit used parison, a sample whose value and coloring power has been ascertained by actual practice.

If a new supply of dye stuff is to be tested, weigh out equal quantities of the standard coloring matter and of the one to be tested (say 10 to 30 grains); dissolve them, using the same quantity of alcohol and water, in vessels of as nearly as possible equal size; introduce in each an equal quantity of white wool; place them on a water bath; raise the temperature gradually, and after sufficient time has elapsed, take the two pieces out, dry should be pure, and especially free from aldehyde; methyl spirit does not appear to injure some of the dyes. Spirit containing shellac turns roseine of a bluish color. 2564. To Distinguish Aniline from Other Dyes. Aniline colors, for dyeing parposes, are now used to such an extent throughout the country as almost to exclude all others, on account of their brilliancy and cheapness.

They are, however, liable to lose in appearance by bright sunlight, and in lustre by the artificial light of gas or candles. It is, therefore, them carefully, and compare them. That desirable to have a ready means by which which has been dyed with the best dye, will, they can be recognized. This is all the more of course, show the fullest, brightest, and necessary, as arsenic acid is generally emclearest color. Instead of testing on skeins of ployed in their preparation; and a cloth that wool, Mr. Shuttleworth recommends small has been dyed with an aniline color containing squares of white merino or cashmere, as af- it may have absorbed a considerable quantity fording a more even surface, and a greater of that dangerous article. The readiest way mass of color. A known weight of the dye should be dissolved in alcohol and added to the bath of warm water, with the necessary mordants. A square of cloth of known weight -say 10 grains-is immersed in the bath, and, after a stated time, removed. The strength for its detection is to boil the flannel, or whatever other cloth it may be, with a solution of caustic soda or potassa, and, after filtering the fluid from the residue, neutralizing it with hydrochloric acid. If the cloth has been dyed with an aniline color, the fluid will show and shade of the color can thus be compared a coloration. Most of the aniline dyes may with previous samples, dyed under like conditions. It is a good plan to paste these squares, by one edge, in a blank book, noting anything worthy of remark on the margin. The colors are thus preserved from the action of the light, and will be found very useful for reference.

2561. Test for Sugar in Aniline Dyes. Aniline blue and aniline green have been found adulterated with a considerable quantity of sugar. Mr. Joly, of Brussels, has also be extracted by boiling alcohol, which process, perhaps, can be performed in less time than the other.