SILURIAN PERIOD 



5385 



SILVER 



should be taken that it is reduced evenly in 

 layers and not taken more from one side than 

 another. The top layer is of course most liable 

 to spoil, especially if it is allowed to become 

 uneven. 



Silage has proved such a great benefit to 

 farmers that it now forms the chief winter food 

 for farm and dairy stock. Certain chemical 

 changes take place during storage, but the food 

 value of silage is about the same as that of the 

 green crop. Dairy cattle, especially, thrive on 

 silage, as it is juicy, nutritious and a good milk 

 producer. Three tons of good mixed silage are 

 equal in food value to one ton of good timothy 

 and clover hay, but it must be remembered 

 that one acre of land planted to corn will pro- 

 duce silage equal to four tons of hay. The 

 cost of .growing and storing silage varies, but 

 may be reckoned as averaging between $1.75 

 and $2.50 per ton. 



There have been many arguments in agri- 

 cultural circles concerning the packing of silage. 

 Some authorities maintain that the corn or 

 other crops should be packed whole; others 

 claim that it should be cut. It is now gener- 

 ally admitted that when cut into short lengths, . 

 the silage packs better, undergoes less fermen- 

 tation and is better preserved than when stored 

 whole. F.ST.A. 



Consult Rabild, Risser and Parks' "Homemade 

 Silos," in Farmers' Bulletin No. 589, United States 

 Department of Agriculture. 



SILURIAN, silu'rian, PERIOD, that divi- 

 sion of geologic time in the Paleozoic Era ex- 

 tending from the Ordovician Period to the De- 

 vonian. It takes its name from the Silures, a 

 people of ancient Britain, where the rocks were 

 first studied. The rock formations were very 

 extensive, and they are found in all the conti- 

 nents. They were chiefly limestones and sand- 

 stones. In the United States and Canada the 

 Niagara, Helderberg, Salina and Onondaga are 

 some of the most important systems. The 

 great salt beds of New York and Michigan 

 were formed during this period, as were the 

 deposits of gypsum and the iron ore of the 

 Appalachian region. The greater part of the 

 Appalachian Mountains was thrown up and the 

 Delaware Water Gap was formed. Life, so far 

 as known, consisted chiefly of shellfish and star- 

 fish forms, corals and sea lilies (crinoids), and 

 fish were beginning to appear. 



Related Subjects. The reader is referred to 

 the following articles in these volumes : 



.Devonian Period Ordovician Period 



; Geology, page 2439 Paleozoic Era 



SIL'VER, a precious metal used from early 

 times for ornamental purposes, utensils, money 

 and jewelry. It is much less valuable than gold 

 among the metals. Silver has a beautiful lus- 

 ter and a whitish color that is referred to in de- 

 scriptions of the sea and clouds. It was known 

 to the ancient Hebrews by a term meaning 

 pale, and the name assigned to it by the an- 

 cient Greeks signifies shining. Its chemical 

 symbol, Ag, is derived from the Latin word for 

 silver, or argentum. 



Properties. Although harder than gold, silver 

 is softer than copper. It is malleable, for it 

 can be beaten into sheets one one-hundred- 

 thousandth of an inch in thickness, or thin 

 enough to transmit light. It is ductile, as it 

 can be drawn into wire finer than human hair. 

 It is second only to gold as a conductor of 

 heat and is surpassed by no metal as a con- 

 ductor of electricity. 



Silver melts at about 1728 F., and when 

 molten has the power of absorbing twenty 

 times its volume of oxygen. Upon solidifica- 

 tion the oxygen is given up, but if the metal 

 cools rapidly and a crust is formed before the 



United States 

 70 



Australasia 



n 



Figures Represent Mil lions of Fine Ounces 



COUNTRIES LEADING IN PRODUCTION 

 Four countries produce each over fifteen mil- 

 lion ounces of silver each year. 



air has escaped, bubbles of gas are formed in 

 the metal and burst through the crust, driving 

 out small ball-like masses of silver. This ac- 

 tion, occurring only in pure silver, is known as 

 "spitting," and may be prevented by adding a 

 small amount of bismuth, copper, zinc, salt or 

 powdered charcoal. Silver is not affected by 

 moisture or dryness, alkalies or vegetable acids, 

 but sulphur or sulphureted air blackens it, and 

 thus it quickly tarnishes in rooms lighted by 

 coal gas. Its noncorrosive properties make it 

 valuable for surgical uses. 



Alloys and Compounds. As silver is too soft 

 to stand constant wear without any hardening 

 element, for commercial purposes it is gener- 

 ally mixed with copper to form what is called 

 an alloy. Such an alloy is used in making coins, 

 jewelry and tableware. The United States sil- 



