324 



THE CENTURY BOOK OF FACTS. 



a sheet of ice which filled up the Baltic and 

 extended into Northern Germany. The Gla- 

 cial Period, or Ice Age, as ifc is also called, is 

 estimated to have begun upward of 200,000 

 years ago, and lasted for 100,000 years. 



Glass. The Egyptians are said to have 

 been taught the art of making glass by 

 Hermes. Pliny says the discovery of glass 

 took place in Syria. Glass houses were erected 

 in Tyre, where glass was a staple manufacture 

 for many ages. This article is mentioned 

 among the Romans in the time of Tiberius ; 

 and it is known from the ruins of Pompeii, 

 that windows were formed of glass before A . 

 D. 79. Italy had the first glass windows, next 

 France, whence they came to England. Used 

 for windows in private houses in the reign of 

 Henry II. of England, 1177, but imported. 

 The manufacture was established in England 

 at Crutched-Friars in 1557. It was improved, 

 1635, and was brought to great perfection in 

 the reign of William the Third. Plate glass 

 for coach windows, mirrors, etc., was made at 

 Lambeth by Venetian artists, 1673. The man- 

 ufacture was improved by the French, who 

 made very large plates ; and further improve- 

 ments have been made in Lancashire, Eng- 

 land, and the United States. 



Glass, Discovery of. There is com- 

 paratively little known in regard to the inven- 

 tion of glass. Some of the oldest specimens 

 are Egyptian, and are traced to about 1500 

 years before Christ (by some, 2300 B. C.). 

 Transparent glass is believed to have been first 

 used about 750 years before the Christian era. 

 The credit of the invention was given to the 

 Phoenicians by the ancient writers. The story 

 of the Phoenician merchants who rested their | 

 cooking-pots on blocks of natron (subcarbonate 

 of soda) , and found glass produced by the union , 

 under heat, of the alkali and the sand on the 

 shore, is a familiar one. The world no doubt 

 owes the art of glass-making to the Egyptians. 

 It was introduced into Rome in the time of 

 Cicero, and among the Romans attained a 

 high degree of perfection. Some of the most j 

 beautiful specimens of glass ever manufactured 

 were made in Rome before the Christian era ; 

 as, for instance, the exquisite Portland vase in 

 the British Museum. During the mid- 

 dle ages the Venetians were the most famous 

 makers of fine glassware, and after them 

 the Bohemians. Though* the art of making 

 glass and blowing it into all kinds of shapes 

 was known so early, this material does not seem 

 to have been used for windows until about A.D. 

 300. 



Glucose, termed also grape sugar, starch 

 sugar, and diabetic sugar, is a natural organic 

 compound, consisting of carbon, hydrogen, 



and oxygen. It is found to some extent in the 

 animal kingdom and very largely in the vege- 

 table kingdom, being a constituent of the 

 juice of almost all sweet fruits and vegetables. 

 The name " diabetic " is due to its large occur- 

 rence in the urinary secretion and other fluids 

 of the body in the disease called diabetes. It 

 is manufactured in large quantities from starch 

 and is used in the manufacture of beer and a 

 coarse kind of alcohol. It is in taste much 

 the same as ordinary sugar, but less sweet . It 

 has a peculiar effect upon a ray of polarized 

 light, passing through it; and there are two 

 varieties comprising fruit sugar, one of which 

 turns the plane of polarization to the right, 

 and is called dextro-glucose, and the other 

 turning the plane of polarization to the left, 

 and called lapvo-glucose, or dextrose and Leva- 

 lose respectively. 



Grain. The origin of its cultivation is 

 attributed to Ceres, who, having taught the art 

 to the Egyptians, was deified by them, 2400 

 B. C. Corn, or grain, provided a common 

 article of food from the earliest ages of the 

 world. The first importation of corn into 

 England of which we have any knowledge was 

 in 1347, though it was introduced into Britain 

 in the sixth century. 



Graphite. The name is derived from 

 the Greek yraphein, to write. It is also com- 

 monly but incorrectly called black lead and 

 plumbago. It contains no lead, but is an 

 allotropic form of carbon, and therefore iden- 

 tical in composition with charcoal and dia- 

 monds. It occurs as a mineral, both massive 

 and disseminated through the rock, generally 

 in granite, gneiss, mica schist, and crystal- 

 lized limestone. It is also a product in the 

 destructive distillation of coal, and can be arti- 

 ficially obtained by other methods in the 

 laboratory. It is lighter than water, and this 

 property is made use of in separating it from 

 the rock in which it is found. The ore is pul- 

 verized and then thrown into large, shallow 

 tanks ; the particles of rock sink, while the 

 particles of graphite float and are taken from 

 the surface free from the rock, and are formed 

 into solid blocks by great pressure. The mine 

 at Burrowdale, in Cumberland, England, has 

 been known since the time of Queen Elizabeth 

 and probably furnished the first lead pencils 

 ever made, but became exhausted many years 

 ago. Large deposits of graphite have been 

 found in the northeastern part of Siberia, and 

 in Germany, France, Austria, and in several 

 portions of the United States. Its most im- 

 portant use is in the manufacture of lead 

 pencils. But, as it is infusible and a good 

 conductor of electricity, it has found other 

 important applications, as for crucibles and 



