A blue coloring matter is made in Holland from the " Turnesol," and imported into other countries in cakes. A considerable quantity is used in France, particularly in the northern departments, where the Holland blue has a high reputation. An attempt has been lately made in that country to manufacture it at home. The tinctorial lichens that form the base of this blue, and whii serve for prepa- j ring it, are the " Rocella Tinctoria," of the Canary Isles, the " Fuciformis " of Cape Verd, the " Tartarens " of Sweden and Norway, the " Lecanora Barella " of Auvergne (France), the " Imbilicaria Pustulata," common in the last-named country, and the " Rocella Fucop-sis, very common on the elevated rocks of the Mediterranean Sea and Atlantic Ocean, and which is also very plentiful on the 'coast of Normandy, and of the Bay of Biscay, —c. There are many other lichens more or less esteemed as tinctorial, in Provence, Langue-doc, Roussillon,- (France), which are previous ly examined to determine the quality of their coloring matter, for this purpose the specimen is first pulverized and the powder placed in a vessel with a little sal ammoniac moistened with a mixture, in equal proportions, of liquid ammonia and lime, the vessel should be only halt filled, so that when the mouth is'stopper-ed it may contain some air. At the expira tion of three or four days the lichen that is be ing tested ought to have turned to a red color. In this manner it is easy to determine the va lue of the various lichens offered for sale ac cording to the degree of intensity of their red coloring. Having selected a preferable lichen it is pounded in a mortar, during which pro cess sufficient water is added to lorm it into a thick paste, this is done to assist in pounding it. Equal quantities of lichen in this state and potash are then taken and mixed up to gether effectually, after which the compound is exposed to fermentation. This is caused by placing it in stone troughs in a building which is heated to a suitable temperature to keep up a continued fermentation until the re action ol the alkali on the coloring matter has taken place. When the paste has been placed in the troughs it is moistened with stale urine or urine containing carbonate of ammonia. This urine, therefore, developes much ammo nia, which acts on the coloring matter; the compound is shaken several times, and after each time the troughs are covered to allow the gas from the ammonia to re-act on the dying substance, more urine being added whenever no further gas is emitted from the substance. The potash is intended to increase the action ot the ammoniated urine on the co loring matter and to give it more strength. At the end of eight or ten days the mixture becomes a dull red, alter twenty-five or thirty days it is a very fine purple red, and ten or twelve days after it changes completely to i blue. In this state ammoniated urine must be added, and the whole to be shaken as often as it seema expedient for about forty days. When the paste has become blue there is add ed one-fortieth part of lime to neutralize the ammonia, by causing a disengagement ot this latter. Dissolved glue, in a suitable quantity, is then poured in to solidify it, and to bind to gether the substances that form the paste. It is of importance that its consistency should be such, that when steeped in warm water it should give to the water its blue color with out dissolving, it it is too liquid it is left to evaporate. When it is of a proper consisten cy it is pounded in a machine to render it finer, and easier to be moulded, and after this placed in moulds and dried in the open air or near a stove. This coloring substance is a sort of lac, the base of which is the ligneous part of the lichen and the alkaline salts, and on which is fixed the coloring matter or the tinctorial lichens changed to blue by the ac tion ot the alkalies. It is used chiefly in France for whitewashing houses, by laun dresses for getting up linen, by sugar refiners, —c. —c.; it is also useful as a substance called Turnesol dye, which is the most powerful agent in determining the presence of free acids, these acids flying to the alkali and changing the dye to a red, which is its essential color. —mdash; [Genie Industriel.
This article was originally published with the title "Manufacture of Blue"