CHEMISTRY. 



91 



for clothing and shoes which will allow the 

 escape of perspiration. The introduction of 

 celluloid, a substance formed by the very close 

 incorporation of gun-cotton and camphor, has 

 given a valuable substitute for hard rubber in 

 many of its uses, a material which may be 

 employed for a multitude of different purposes. 

 Improvements in Glass-making. By reason 

 of the greater accessibility of purer materials 

 for glass-making, it has been possible to replace 

 the coarser green glassware formerly in use for 

 many common purposes with colorless glass. 

 Greater pains have been taken to ascertain and 

 use the best proportions of the materials with 

 a view to homogeneity and definiteness of com- 

 position in the glass, so as to dimmish the risk 

 of "devitrification" and the liability of the 

 surface of the glass when in use to alteration 

 by water or other reagents. The Siemens re- 

 generative furnace with gaseous fuel has been 

 so adapted as to dispense with the glass-pots 

 formerly in use, and allow the preparation of 

 the glass to be completed in the hearth itself, 

 where, in three separate compartments, are 

 performed in succession the processes of fusing 

 the mixture of raw materials, "fining" the 

 glass, and bringing it down to the proper tem- 

 perature and consistence for working. For the 

 production of glass in sheets for windows, the 

 " crown-glass " process of " Hashing " has near- 

 ly ceased to be employed, while a marked ex- 

 tension and improvement has taken place in 

 the scale on which the product is turned out 

 under the cylinder process, in the size of the 

 sheets that are made by it, and in the smooth, 

 even condition of the surface of the flatted 

 sheets. Plate-glass has been brought more 

 and more widely into use, and plates of very 

 large size have become familiar. The limit of 

 size of these plates is, in fact, found in the diffi- 

 culty of moving the slabs and setting them, 

 rather than in that of producing them. In the 

 manufacture of hollow ware, the process of 

 pressing in molds has been developed very rap- 

 idly, and much varied ingenuity has been shown 

 as to the details of the molds and other tools. 

 The various processes for producing an an- 

 nealed or toughened glass have given us a ma- 

 terial of largely increased strength, and capable 

 of withstanding great mechanical stress and 

 quite violent blows, but which has other quali- 

 ties tending considerably to limit its useful- 

 ness. The progressive improvement in the 

 manufacture of optical glass is shown in the 

 steady increase in the size of the disks from 

 which the largest telescopic lenses are made, 

 which may now be obtained more than thirty 

 inches in diameter, and in their clearness, uni- 

 formity^ and freedom from flaws. The deco- 

 ration of glass-work has advanced more in an 

 artistic than a technical direction. Imitations 

 of the precious stones are made with remark- 

 able fidelity to natural appearance, and with a 

 degree of hardness exceeding anything that was 

 known some years ago. To the older varieties 

 of "milk-glass," or enamel, has been added the 



" hot-cast porcelain," made by fusing together 

 quartz-sand, cryolite, and zinc oxide, which is 

 chiefly used for less artistic articles. The prod- 

 ucts of the revived glass industry at Murano well 

 deserve attention. In the surface-enameling of 

 sheet-glass, lace-patterns are transferred from 

 the woven or netted fabric itself, by using it 

 as a stencil to distribute upon the surface the 

 pulverized enamel which is afterward to be 

 burned on. Tilghman's sand-blast supplies a 

 process for etching on glass of great and per- 

 manent value on account of its simplicity and 

 quickness, its efficiency in deep cutting, its ap- 

 plicability to very large sheets, and the deli- 

 cacy with which the minute features of intri- 

 cate designs may be engraved by it. Iridescent 

 glass, exhibiting a delicate play of soap-bubble 

 colors, is produced by slightly attacking the 

 surface of glass with moderately strong liquid 

 hydrochloric acid under pressure in close ves- 

 sels, or with the fumes from chloride of tin or 

 analogous material volatilized in a reheating 

 furnace. Dode's process for platinizing glass, 

 by carefully heating it after the surface has re- 

 ceived a nicely applied thin coating of platinic 

 chloride mixed with one of the essential oils, 

 has the advantage of furnishing a mirror which 

 reflects from the front face, avoiding the double 

 passage of light through the glass itself. The 

 exposed metal is not liable to tarnish. Quite 

 an effective camera lucida may be made from 

 a piece of flat sheet-glass treated in this way. 

 The platinum film is thin enough to permit the 

 pencil and hand of the draughtsman to be seen 

 through it, while at the same time the objects to 

 be copied are seen by reflection. Glass drawn 

 out into extremely fine threads, or "glass-wool," 

 has been used for decorative purposes, and as a 

 material for filtration. 



The greatest improvement in the manufac- 

 ture of ceramic wares has taken place in the 

 higher grades of stoneware and earthenware 

 rather than in porcelain, and those wares have 

 received almost the same degree of care and at- 

 tention as have been given to porcelain itself. 

 The most valuable mechanical appliance lately 

 brought into use is the filter-press, which is 

 employed for removing the surplus water from, 

 the clay after the mixing has been performed. 

 Some of the presses are adapted to prevent the 

 inclosure of air-bubbles in the clay. The re- 

 generative furnace has been adopted with ad- 

 vantages which are shown in the saving of fuel 

 and the reduction of the number of pieces of 

 ware spoiled in the firing. In the decoration 

 of pottery- wares, painting by hand has been to 

 a large extent replaced by the transfer of print- 

 ed patterns and designs. Metallic lusters are 

 applied with more successful effect than for- 

 merly, and a peculiar surface appearance re- 

 sembling that of mother-of-pearl is given to 

 the ware by a lustrous bismuth glaze. 



The Chemistry of Arsenical Poisoning. 

 0. Binz and H. Schulz have offered a new ex- 

 planation of the chemical cause of the poison- 

 ous nature of arsenic. The theory of Liebig, 



