DYEING WITH LO-IIAO.

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obtained has only been known to the Chinese themselves since about thirty-fiveyears. It is quite certain, also, that no mention whatever is made of Chinesegreen and the use of the barks, for any purpose whatever, in the otherwisevery-corredtly written and published Chinese books on botany and agricultureissued about the middle of the last century.

French Process for Dyeing with Lo-kao.

E. Michel, at Lyons, dyes silk green (Vert-Venus, Vert-Azof, or Vert-Lumiere, the latter appellation being given because this green colour does notappear blue when seen in artificial light) by soaking in an aqueous solution ofalum (sp. gr. 1-034), for three days, a quantity of 5 grms. of lo-kao and30 grms. of the solution just alluded to. The pigment is next thoroughlyincorporated with the solution of alum by stirring and rubbing with a glassrod, while the fluid is simultaneously diluted by the addition of 250 grms. ofthe alum solution ; the liquid is left again standing for twenty-four hours, andthen carefully decanted from any sediment. The colour of this fluid is verydeep green, nearly black. This operation is repeated with a fresh quantity ofpigment, so as to obtain at least a litre of the solution, which keeps very well.M. Michel found that if to this solution of lo-kao a sufficient quantity ofspring water were added, containing lime salts, there ensues gradually a pre-cipitate of a calcareo-aluminous lake, and he contrived to find, by a series ofexperiments, what quantity of such spring water would be required for obtaininga fluid from which this lake did not precipitate immediately, or even after alength of time, but which yet possessed the property of depositing thecolouring matter it contains on the fibre of textile fabrics when they come intocontadt with it. The quantity of spring water at Lyons required for 1 litre oflo-kao solution was found to be 15 litres : in a solution of that descriptionsilk was dyed without any other precaution than a slight deviation of tem-perature, and the depth of the shade is regulated by the number of repeatedimmersions. He found that, in consequence of the various operations silk issubmitted to before being dyed, it contains a small quantity of lime-salts,which adt in this case as a mordant; but in some cases the silk might advan-tageously be immersed in spring water containing lime before the dyeingprocess. Instead of using the lo-kao of commerce, it is preferable to applyit in the purified state prepared according to the method of M. Persoz,described above.

The following is another method for dyeing with lo-kao, suggested byPersoz:—The lo-kao is dissolved in a moderately strong and slightly acidu-lated solution of tin-salt, and the silk is immersed in this liquid and kept atthe ordinary temperature : it assumes a pale salmon-colour, and is nextwashed in a liquor made up of ammonia, potassa, or acetate of lime. Thecolour thereby becomes first purple, and next blue, and the blue is convertedinto green by dyeing in a cold infusion of Persian berries: the silk may, ifpreferred, be aluminised first, and next put into a solution of lo-kao in sulphy-drate of ammonia. After the immersion of the silk in this liquor it isthoroughly aged, and in order to obtain the requisite depth of shade theimmersion is'repeated once, twice, or oftener. The lo-kao may also be firststeeped in a weak alkaline lye, and next saturated with hydrated protoxide oftin; the silk is placed in this solution, and the fabric exposed to air, when it

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