M. TECHNOLOGY. 495 



the great floods, and which sunlight bleaches snow-white. 

 Some were disposed at first to regard it as an accumulation 

 of vegetable fibres, collected and felted by the action of water. 

 In the last two years it has become an article of trade in that 

 region, and it is used extensively as a lining for garments of 

 peasants. A material called Pulu was exhibited in the Chi- 

 nese department, which seemed to surpass in every respect 

 Kapok, the vegetable wool of the Bombax ceiba, etc., of Java, 

 introduced by Kratzenstein & Co., of Amsterdam, for stuffing 

 beds, furniture, etc. The Pulu is a gold-brown fibrous mate- 

 rial, of silky lustre and exceeding softness and fineness, pos- 

 sessing a very high degree of elasticity for vegetable fibre, 

 and is probably identical with a substance collected very 

 largely in the Sandwich Islands from the tree fern, and ex- 

 ported under the same name. Solinas, of Alexandria, exhib- 

 ited a collection of fibres prepared from Nile reeds, and iso- 

 lated so carefully and of such length as to make a favorable 

 impression. A specimen of the Welwitschia mirabilis, of Ben- 

 guela, was shown in the Portuguese department, a plant per- 

 haps never before seen in Europe, and well deserving the 

 name mirabilis. Its long leaves are very rich in tough fibres, 

 which could doubtless be utilized. 32 C 9 Oct. 18, 1873, 315. 



BICHROMATE OF POTASH IX DRESSINGS FOR FABRICS. 



Certain thickening materials, as gum, dextrine, and especial- 

 ly glue, when mixed with a very small quantity of bichro- 

 mate of potash, as is well known, become totally insoluble in 

 water after exposure to diffused as well as direct sunlight a 

 fact made use of in the carbon-photographic printing process. 

 An equally valuable application consists in the employment 

 of gelatine, with the addition of a small amount of bichro- 

 mate of potash, for dressing and water-proofing linen, silk, and 

 cotton fabrics. Thus, if the cloth is saturated with a solu- 

 tion of gelatine, to which about one fortieth or one fiftieth of 

 bichromate has been added, and then dried and exposed to 

 the sunlight, the dressing becomes so fixed to the material 

 that scarcely any agent will remove it. In this manner, fab- 

 rics, whether of cotton, linen, or silk, may be rendered water- 

 proof, for use as umbrellas, cloaks, etc.; or, if the gelatine 

 mass be thick enough, they will even be rendered impermea- 

 ble to gases. 14 C, 1873, CCIX., 371, 



