540

DYEING AND CALICO PRINTING.

hydrochloric acid (muriatic acid) is present, or, if nitrate of soda has beenfound, it may have been contaminated with common salt.

To deleft alumina, a little of the sample is boiled with a mixture of nitricand hydrochloric acids, to peroxidise any iron that may have remained in thestate of protoxide. Pure caustic soda (prepared from metallic sodium) is dis-solved in a little water, and added to the sample thus treated in decided excess.It is then boiled in a clean iron vessel, and filtered. To the clear filtrate asolution of chloride of ammonium is added. If a white precipitate appearsalumina is present.

In order to determine whether any part of the iron present in a sample is inthe state of protoxide or not, a solution of carbonate of soda is slowly droppedin. If the sample is a pure peroxide salt, all the iron present being broughtto the highest state of oxidation, the precipitate formed will be uniformly paleyellow. If any protoxide be present a greenish or olive turbidity will appearin the liquid.

It may sometimes be required to find the comparative acidity of twosamples of nitrate of iron. For this purpose bring both to the same specificgravity, by adding water to the stronger, and noting the quantity required.Equal measures of the two samples are then taken, and into each of them astandard solution of carbonate of soda is run from a burette, stirring aftereach drop, till the exaft point is reached, when the liquid is neutral to litmus-paper. The number of degrees consumed in each case gives the respeftiveacidity of the samples.

But in the most important points—namely, the purity, brightness, perma-nence, and evenness of the shades produced—the only method to decideon the quality of a sample of nitrate of iron is to dye with it on a smallscale.

In order to test “blue iron” equal measures of each sample are dilutedrespeftively with equal quantities—about five or six times their own bulk—ofcold distilled water. Equal weights of clean calico or of cotton-yarn are thenallowed to soak in each sample for an equal length of time. The swatchesare then taken out and allowed to drain. Meantime, equal measures of asolution of prussiate of potash, diluted with equal quantities of water, areplaced in a number of glasses of suitable size, and in these the swatches arerespeftively steeped for an equal length of time. They are then taken out,rinsed in cold water, dried, and compared.

“ Black irons” are tried by taking a number of equal swatches of cleancalico, and steeping the whole of them in a solution or decoftion of someastringent—such as galls, myrobalans, sumac, &c.—for one hour. They aretaken out and allowed to drain, and are then placed respeftively in the differentsamples of nitrate of iron, two fluid drachms of each being diluted for thispurpose with half a pint of cold water. After soaking for ten minutes theswatches are taken out, rinsed in cold water, dried, and compared.

For testing “ common irons,” swatches treated as above are steeped in aweak solution of alum. That which is least affefted by this treatment ispreferred.

The following iron mordant is recommended by some dyers as safe anduseful:—Dissolve 78 lbs. red oxide of iron in 117 lbs. sulphuric acid. Dilutewith water, and add 17 lbs. of sulphate of potash, and allow the compound to