130 



THE POPULAR EDUCATOR. 



There is a form of calc spar, called aragonite, which appears 

 in six-sided prisms ; hence carbonate of lime is said to be 

 dimorphous. In the lesson on "Water," it was said that 

 although carbonate of limo is insoluble in pure water, yet if 

 any carbonic acid be present, the water becomes capable of hold- 

 ing this salt in solution, rendering the water hard. By using 

 such water, thick crusts become deposited in boilers. This evil, 

 however, may be obviated by the addition of a little sal- 

 ammoniac to the water. By a double decomposition, soluble 

 calcium chloride and volatile ammonium carbonate are formed 

 CaCO, + 2NH.C1 = CaCl> + 2 (NH 4 ) CO,. 



Calcium Sulphate (CaSOJ is found combined with two mole- 

 cules of water, as gypsum or plaster of Paris. When trans- 

 parent it is named selenite. When heated to 130, it decrepitates 

 on giving up its water of crystallisation. When this powder 

 (plaster of Paris) is made into a paste, the mixture " sets " in a 

 few moments. Stucco is plaster of Paris mixed with a solution 

 of size. 



Calcium Chloride (CaCl 2 ) is formed when marble is dissolved 

 in hydrochloric acid. When crystallised it contains six atoms 

 of water. When heated it parts with four of these atoms, and 

 the porous mass which remains, exhibiting a great avidity for 

 moisture, is used in the laboratory for drying gases. 



Bleaching Powder has been before treated of. 



Calcium Fluoride (CaF 2 ), or Fluor-spar, the Blue-John of 

 the Derbyshire miners, crystallises in cubes (Fig. 496). Its 

 colour varies. Eose colour is the most rare, and purple the 

 most common. It is sometimes used as a flux to reduce 

 metals ; hence its name. 



Calcium Phosphate (3Ca2P0 4 ) forms jj of the bones of animals, 

 and is the source from which phosphorus is derived. 



Calcium Sulphide may be formed by the action of sulphu- 

 retted hydrogen on red-hot lime. It is not soluble in water, but 

 is gradually decomposed by it. Thus 



2CaS + 2H 3 O = CaH 2 + CaH,S a . 



When milk of lime and flowers of sulphur are boiled together, 

 a yellow solution is obtained, which consists of calcium penta- 

 sulphide (CaS s ) and calcium hyposulphite (CaO,S,O.). There 

 are other salts of lime of less moment. 



MAGNESIUM. 



SYMBOL, Mg COMBINING WEIGHT, 24 SPECIFIC GRAVITY, 17-t. 



Magnesium is closely allied to zinc and cadmium, but is gene- 

 rally placed in this class, sihce its oxide has an alkaline reaction. 

 Its salts occur in the sea ; but dolomite, or magnesium limestone, 

 contains 35 per cent, of the carbonate. The metal may be pre- 

 pared by heating together the chloride with sodium. Sodium 

 chloride is formed whilst metallic magnesium distils into the 

 receiver. It is a white metal, fuses at a low red-heat, and 

 burns into MgO with great brilliancy at a higher temperature. 

 The magnesium light is so rich in " actinic " rays, that it is 

 used instead of sun-light for photographic printing. 



Magnesia (MgO), the only oxide of the metal, is usually pro- 

 cured by heating the carbonate as in the case of lime. Like 

 that substance it forms an hydrate, but without an elevation of 

 temperature. 



Magnesium Chloride (MgCl 2 ) is obtained for the manufacture 

 of the metal by dissolving one part of magnesia in hydro- 

 chloric acid, and adding three parts of sal-ammoniac in solution, 

 then evaporating to dryness. By igniting this in a covered 

 crucible, magnesium chloride alone is left. 



Magnesium Sulphate (MgSO 4 ) is known by the name of Epsom 

 Salts, since it occurs abundantly in the springs at Epsom. It 

 is made in large quantities from sea- water, to which it imparts 

 the bitter taste of all the soluble salts of this metal. 



Magnesium Carbonate (MgC0 3 ) is found native as a mineral, 

 called magnesite. The common magnesia of the shops is pre- 

 pared by boiling magnesium sulphate and a solution of sodium 

 carbonate. It is sparingly soluble in water ; but if the water 

 contain carbonic acid, it can take up a large quantity of the 

 salt, forming 1 " fluid magnesia." 



Combined with silica, magnesia is found in many minerals. 

 Soap-stone, meerschaum are hydrated silicates of magnesia. 

 Serpentine, hornblende also contain magnesia. All the conv 

 pounds of magnesia may be recognised by the fact that they 

 acquire a pink tinge when heated with the nitrate of cobalt in 

 the blow-pipe flame. 



HISTORIC SKETCHES. XXX. 



THE PERSIAN POWEB. 



THE book of the prophet Daniel would alone be sufficient to 

 make one desire to know more of Persian history than is given 

 in the Bible. Full of interest, indeed, is the story of thia 

 ancient kingdom and of its people. 



The very remote history of Persia is involved in much 

 obscurity. The country was most probably, in spite of semi- 

 independence, attached to a neighbouring empire, and certainly 

 in the year 900 B.C. we find it forming an integral part of the 

 Assyrian dominions, and when these fell to pieces Persia did not 

 become free, but was incorporated in the kingdom of Media. 

 The union was not a happy one, and the Persians sought every 

 opportunity to break it off. They found themselves in the 

 position of thralls to men of a civilisation inferior to their own, 

 bound down strictly to religious rules and observances with 

 which they had no sympathy. Even when they had succeeded 

 in inoculating the minds of their masters with their own 

 religion, the magi, the priest-rulers of Media, took upon them- 

 selves the administration of the priestly duties, and asserted in 

 the most tender places the right of the strongest to dominate. 

 The religion of the Persians was that which their own prophet 

 or philosopher, Zoroaster, had taught them more than a thousand 

 years before the birth of Christ. It had in the course of that 

 time become corrupted, insomuch that the original belief in one 

 supreme God had become almost lost. Upon a comparatively 

 pure system all sorts of gross superstitions, borrowed from the 

 nations with whom the Persians had to do, were engrafted, 

 until the worship of the sun, moon, and stars, became a leading 

 feature of the religion. Fire, as symbolising the light of the 

 world, was worshipped by the disciples of Zoroaster, who did 

 not however omit, as their descendants did, the adoration of 

 Him who was symbolised by the fire. 



Zoroaster was the first, we might also say the last, who 

 endeavoured to reconcile in his creed the existence of moral 

 and physical evil with the attributes of a beneficent Creator 

 and Governor of the world. " The first and original Being, in 

 whom or by whom the universe exists, is denominated in the 

 writings of Zoroaster, Time without bounds." . . . "From 

 either the blind or intelligent operation of this infinite Time, 

 which bears but too near an affinity with the chaos of the 

 Greeks, the two secondary but active principles of the universe 

 were from all eternity produced, Ormuzd and Ahriman, each of 

 them possessed of the powers of creation, but each disposed, by 

 his invariable nature, to exercise them with different designs. 

 The principle of good is eternally absorbed in light ; the prin- 

 ciple of evil eternally buried in darkness. The wise benevolence 

 of Ormuzd formed man capable of virtue, and abundantly pro- 

 vided his fair habitation with the materials of happiness. By 

 his vigilant providence, the motion of the planets, the order of 

 the seasons, and the temperate mixture of the elements are 

 preserved. But the malice of Ahriman has long pierced 

 Ormuzd's eggs, or, in other words, has violated the harmony of 

 his works. Since that fatal irruption, the most minute particles 

 of good and evil are alternately intermingled and agitated 

 together; the rankest poisons spring up amidst the most salu- 

 tary plants ; deluges, earthquakes, and conflagrations attest the 

 conflict of nature ; and the little world of man is perpetually 

 shaken by sin and misfortune. While the rest of human kind 

 are led away captive in the chains of their infernal enemy, the 

 faithful Persian alone reserves his religious adoration for his 

 friend and protector Ormuzd, and fights under his banner of 

 light in the full confidence that he shall in the last day share 

 the glory of his triumph. At that decisive period, the 

 enlightened wisdom of goodness will render the power of 

 Ormuzd superior to the furious malice of his rival. Ahriman 

 and his followers, disarmed and subdued, will sink into their 

 native darkness ; and virtue will maintain the eternal peace and 

 harmony of the universe." 



The simplicity of the Persian worship is vouched for by 

 Herodotus ; indeed, it seems to have impressed ail who came in 

 contact with it. " That people," says the Greek historian, 

 " rejects the use of temples, of altars, and of statues ; and 

 smiles at the folly of those nations who imagine that the pods 

 are sprung from, or bear any affinity with, the human nature. 

 The tops of the highest mountains are the places chosen for 

 sacrifices. Hymns and prayers are the principal worship ; the 



