G68 GLASS 



therefore, which, in London, in 1826 exceeded Is. IQd. on each superficial foot of 

 glass, is now about 2d. per foot. Sand also, which is its base, forming as it does 

 nearly three-fifths of its composition, is obtained near London at 3s. Qd. anl up- 

 wards per ton, of a quality superior to Lynn sand formerly used at 18s. per ton. 

 The direct charge of labour in 1826 exceeded Is. 6d. per foot; now the average rate 

 of wages for skilled labour is higher by 20 per cent, than forty years ago. In 1819 

 two furnaces, each having a huge chimney-shaft, were required to produce 1,000 feet 

 per week, while at the present time two furnaces, with only one chimney-shaft, 

 suffice for the production of 12,000 feet, with the same, if not a less, consumption 

 of fuel. Similarly, though in a less degree, grinding and polishing benches which 

 then finished 200 feet each per week, now accomplish 500 feet to 700 feet, which, 

 by judicious means, may be still further increased to 1,000 feet and upwards. By 

 these means the whole cost has been reduced to nearly the price of common duty- 

 paid window-glass thirty years ago ; and whereas in 1819 the British make was 

 3,000 feet per week, sold at 205. to 25s. per foot, it is now 140,000 feet, selling at 

 2s. and upwards according to quality. The former superior make of this country 

 has, indeed, been greatly neglected, and this has led to a very large increase in 

 the import of the finest fabrics of France and Belgium, so that these imports 

 amounted in 1862 and 1863 to about 16,000 feet per week, and those countries have 

 had a corresponding sale in foreign markets in the absence of such supplies from 

 England ; but still the exports of British plate-glass have increased about tenfold 

 since 1849. 



At home, glass is now extensively used in slabs for flooring and underground 

 purposes, combining as it does greater strength than the York flag, with the addition.! 1 

 advantage of conveying light ; and slabs tested at Woolwich dockyard have been found 

 to bear a pressure exceeding a ton weight. Many years ago, a supply of such slabs 

 was required for the purpose of flooring a palace of one of the native princes of India, 

 but the Excise restrictions then prevailing precluded its supply from England at less 

 than 30s. per foot ; it could now be afforded at 3s. to 4s. In fact, its true position 

 has yet to be attained, when the resources of this country shall have stimulated that 

 more full development of which it is susceptible, and Great Britain shall, as the author 

 of the freedom of this industry predicted, ' supply almost the whole world.' 



Bohemian Glass. M. Peligot states that the hard glass of Bohemia is composed of 

 100 parts of silica, 12 parts of quicklime, and only 28 parts of carbonate of potash. 

 These proportions give a glass quite unmanageable in ordinary furnaces ; but the 

 addition of a comparatively small quantity of boracic acid is capable of determining 

 fusion, and the result is a glass having all the requisite limpidity at a high tempera- 

 ture, and possessing at the same time a great brilliancy and hardness. 



The Bohemian glass is, within certain limits, perfectly elastic, and very sonorous ; 

 when well made, it is sufficiently hard to strike fire with steel, and is scratched with 

 difficulty. The lead glasses, on the other hand, have but little hardness, and h-s in 

 proportion as they contain more oxide of lead; besides which they rapidly lose their 

 brilliancy by use. 



The silica which is employed in Bohemia in the manufacture of glass is obtained by 

 calcining crystalline quartz, and afterwards pounding it while dry. When the quartz 

 has been heated to a cherry-red, it is withdrawn from the fire, and thrown imme- 

 diately into cold water. 



Almost all the Bohemian glass is a potash-glass, because soda and its salts give to 

 glass a sensible yellowish tint. The limestone which is used is as white as Carrara 

 marble. The clay employed for the crucibles is very white, and consists of silica, 

 1.3^, ; alumina, 40-^j ; and water, 13$,. 



The manufacture of glass in Bohemia is of very high antiquity, and the same pecu- 

 liarities have always belonged to the true Bohemian manufacture. 



In our modern times the Bohemian glass has been more especially celebral 

 the beautiful varieties of colours which are produced. See GLASS, COLOUKKD. 



Venetian Glass. From an early date the city of Venice has been celebrated for its 

 glass: the reticulated glass, the crackle glass, and the glass paper-weights, or milLjir<\ 

 are all due to the Venetians. 



The manufacture of glass beads at Murano, near Venice, has been carried on fr an 

 indefinite period, and Africa and Asia havo been supplied from their glass-houses. 

 The process is most ingeniously simple. Tubes of glass of every colour, are drawn 

 out to great lengths in a gallery adjoining the glass-house pots, in the same \\ayas 

 the more moderate lengths of thermometer and barometer tubes are drawn in our 

 glass-houses. These tubes are chopped into very small pieces of nearly uniform 

 length on the upright edge of a fixed chisel. Thei lementary cylinders 1..-iiig 

 then put in a heap into a mixture of fine .sand and wn<>.[-ashes, are stirred al>.ur. 

 with an iron spatula till their cavities got filled. This furious mixture is n<>\\ 



