212 ANNUAL OF SCIENTIFIC DISCOVERY. 



some very beautiful tints similar to those furnished by cochineal. For 

 this purpose, the indigenous rhubarb, contrary to what would have 

 been supposed, furnished the most brilliant red. The dyed specimens, 

 after an exposure to the sunlight for a considerable length of time, did 

 not experience the slightest change. These results may lead to the 

 cultivation of the rhubarb as a dyeing material becoming of consider- 

 able importance. 



A new material for dyeing yellow, called wongshy, has been re- 

 cently exported from Batavia to Hamburg, and examined by M. Stein. 

 It consists of the seed-vessels of a plant belonging to the family of the 

 Gentianeas. The wongshy readily gives up to water, both at the 

 usual temperature as well as on boiling, a coloring matter which pos- 

 sesses such an enormous divisibility, that 2 parts of the capsules when 

 pounded furnish 128 parts of a liquid, which, when placed in a cylindri- 

 cal vessel of white glass with a diameter of three inches, still appears 

 of a bright wine-yellow color. Continued experiments made by M. 

 Stein show that the wongshy will undoubtedly prove a valuable addition 

 to the vegetable dyeing materials. Journal fur Praktische Chcmie. 



The London Journal of Arts for June contains a notice of some 

 experiments upon morindin, a ne\v coloring matter, closely resembling 

 madder, and furnishing a deep red color. Its extraction and application 

 are apparently attended with such difficulty that it will not be of much 

 value economically, though very interesting in a chemical point of view. 



ARSENIATE OF COPPER AS A PIGMENT. 



THE arseniate of copper is a substance possessing a very fine blue 

 color, and seems worthy of occupying a high place in the list of sub- 

 stances employed in water-color painting ; it is permanent, of a rich 

 and beautiful tint, and may be used under all circumstances in which 

 water can be made the vehicle of its application. A communication 

 on the subject of this color has lately been presented by M. Rebou- 

 leau to the French Academy, from which we take the following. If 

 a mixture of equal parts of arseniate of copper and neutral arseniate 

 of potash be heated, it will undergo fusion, and form upon cooling a 

 greenish-blue mass, transparent, very fusible, and having a vitreous 

 fracture ; this is the double arseniate of potash and copper. If, when 

 the arseniates just mentioned are in a state of perfect fusion in a cru- 

 cible, nitrate of potash (to the extent of one fifth of the weight of the 

 fused mixture) be projected into the fluid, in successive small quanti- 

 ties, there will arise a lively effervescence, with evolution of the deu- 

 toxide of nitrogen ; and the crucible when cold will be found to con- 

 tain a magnificently colored blue substance, consisting of the subar- 

 seniate of potash and the arseniate of copper, in combination with each 

 other, and mixed with nitrate of potash. When the compound thus 

 produced is treated with water, the double salt is decomposed, the ar- 

 seniate and nitrate of potash are dissolved out, the arseniate of cop- 

 per, of a beautiful blue color, remaining behind. In the production 

 of the blue arseniate of copper, it appears that the change from the 

 green color of ordinary arseniate takes place at the moment when the 



