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DYEING AND CALICO PRINTING.

There are many other methods of preparing soda from the sulphate, but wemust refer our readers to works on technology for the detail of the severalprocesses.

The value of a soda depends upon the quantity of anhydrous carbonate ofsoda it contains, ascertained by the following method of titration :—

ioo grains of soda are weighed out and dissolved in 500 grains of water ina titration glass. Into another 500 grains of concentrated sulphuric acidare introduced, and the acid is added to the alkali grain by grain untilit readts neutral to test-paper. The loss in weight is the loss of carbonicacid, and as 4i'43 parts by weight of carbonic acid correspond to 100 partsby weight of anhydrous carbonate it is easy to estimate the quantity of truecarbonate contained in a given sample. For example : Suppose the loss ofcarbonic acid equals 38, then

4i'43 : 100 = 38 : 917 per cent of anhydrous carbonate of soda.

If the soda should contain caustic soda, this must be converted into car-bonate before titration by boiling for some time with carbonate of ammonia.

The soda should entirely dissolve; but if a residue remain this must berepeatedly lixiviated until the wash-water no longer causes turmeric paper tobecome tinged. This wash-water should be added to the solution, and thetitration proceeded with as if the soda were entirely soluble.

When treating of alkalimetry we shall speak in more detail of the processof estimating the value of alkalies.

Silicate of Soda.

Silicate of soda, or soda water-glass (Na 0 ,Si 0 2 ) may be prepared by fusingtogether 45 parts of quartz sand, 23 parts of calcined soda, and 3 parts ofcarbon; or more simply by fusing 100 parts of pulverised quartz, and 60 partsof calcined Glauber-salt with 15 to 20 parts of carbon, pulverising the fusedmass, and treating it with boiling water.

In a fluid condition water-glass may be diredtly prepared by heating finelypulverised quartz with a strong solution of caustic soda in an iron vessel undera pressure of 8 atmospheres.

In a dry condition soda water-glass can be prepared by fusing together theingredients in the foregoing proportions. Water-glass in a pure state andfree from sulphur may be prepared by fusing, for twelve hours, 120 parts byweight of finely pulverised quartz with 100 parts of best calcined soda and aquantity of carbon (coal). By this method a water-glass can be obtained asclear, hard, and colourless as the best window glass. From this produdt fluidwater-glass may be prepared by boiling with copper scales for ten hours untilthe liquid acquires a density of 34 0 B. Water-glass thus obtained is especiallysuited to the printer. It is employed as a substitute for dung, but principallyfor fixing ultramarine-blue and pigment colours. The colour is well trituratedwith a solution of silicate at go° Tw.; then printed on without thickening, driedin a cool place; the colour being fixed by passing the fabric through a solutionof chloride of ammonium or of common salt. But an unsatisfadtory harshnessis imparted to the cloth, and the colour is apt to come away in the fixing bath.It serves also in place of borax in the bath for dyeing Nicholson and Guernseyblues and Pomona greens.