CHAMBERS'S INFORMATION FOR THE PEOPLE. 



from it by a process invented by the late Mr 

 H. L. Pattinson, in which the calcined material 

 is submitted to the action of carbonic acid 

 and water under pressure. On account of the 

 diminished use of them in medicine, Epsom salts 

 are now made in much less quantities than in 

 former years. Some dolomites are used as litho- 

 graphic stones, but the best of these are obtained 

 from the oolitic limestone of Solenhofen, in the 

 Bavarian Jura. 



Marl Calcareous Sand. In several geological 

 formations, what are called marl deposits occur. 

 The term marl is properly applied to clay with a 

 variable admixture from 10 to 70 per cent. of 

 lime ; but sometimes a mixture of clay and sand 

 is called marl. Shell-marl is formed by the 

 decomposition of fresh -water shells, mixed to 

 some extent with clay or earthy matter, and is 

 found at the bottom of old lakes. Most marls 

 form remarkably fertile soils, and when the pro- 

 portion of lime in them is considerable, they are 

 useful manures, a property which has been known 

 from very early times. Calcareous sand is formed 

 of fragments of shells or coral, more or less mixed 

 with silicious sand or other substances. 



Gypsum Alabaster. Gypsum, or calcium 

 sulphate, is a highly useful mineral, found abun- 

 dantly in England and many other countries, 

 especially in the New Red Marls. Near Pans, it 

 is found in the Tertiary deposits. There are 

 several varieties of this substance known by 

 different names : when colourless, transparent, 

 and crystallised, it is called selentte, when finely 

 granular and translucent, it is known as alabaster, 

 or if fibrous, as satin spar. The plainer masses 

 of gypsum are calcined to produce plaster of 

 Paris or stucco, a material extensively used in the 

 arts and manufactures. 



The finer kinds of alabaster are used as orna- 

 mental stones, the working of which, like that of 

 marbles, forms an important industry in Italy, 

 where they occur extremely pure and compact at 

 Volterra and La Castellina, in Tuscany. These 

 are largely made into statues, vases, timepiece 

 stands, and other works of art, in Florence. 

 The alabaster found in Derbyshire and Stafford- 

 shire is also used for ornamental purposes, but 

 chiefly for objects of a small size. Alabaster is 

 more soluble in water than marble, and, therefore, 

 is even less fitted for external work. Some ala- 

 baster can hardly be distinguished from marble by 

 the eye, but it is much softer. What is called 

 oriental alabaster is a stalagmitic carbonate of 



lime. , 



When gypsum is cautiously heated 

 500 F., it forms an artificial anhydrite, well 

 known in commerce as plaster of Paris or stucco. 

 The calcined gypsum can then be formed into a 

 cream or paste with water, which after a short 

 time solidifies or sets, and is soon reconverted 

 into gypsum. This property makes plaster of 

 Paris a substance of great value in making moulds 

 for, or taking casts of, objects of art or utility. 

 The greatest consumption of it in Great Britain is 

 for making the moulds used in the manufacture 

 of pottery ; but it is also much used for internal 

 architectural ornaments, in the preparation of 

 cements and artificial marbles (scagliola), in the 

 hardening of some kinds of paper, and for many 

 other purposes. Fictile ivory is plaster of Pans 

 soaked in wax, spermaceti, or stearine. The 



G'.'2 



total annual consumption of gypsum in Great 

 Britain is supposed to be about 30,000 tons, and 

 its value about .10,000. 



Apatite Phosphate of Lime. Apatite or native 

 calcium phosphate has now become a mineral of 

 considerable importance in the preparation of 

 artificial manure. It is imported in shiploads for 

 that purpose from Krageroe in Norway. A still 

 more valuable deposit of it, called sombrerite, is 

 found in the small island of Sombrero in the West 

 Indies. The organic remains, called coprolites, 

 also extensively used for manure, consist for the 

 most part of calcium phosphate. In Spain, some 

 massive and marble-like varieties of apatite are 

 used as building-stones. 



Coral. In our number on ZOOLOGY are noticed 

 those compound zoophytes which secrete or in 

 some way produce reef, precious, and other 

 kinds of coral. Reef coral is a calcium car- 

 bonate, occasionally forming large islands in the 

 Pacific and Indian Oceans, as well as long 

 fringing reefs which extend along the coasts 

 of countries washed by these seas. One of 

 these barrier reefs, on the north-east coast of 

 Australia, extends in a continuous line to a length 

 of about 350 miles. The polypes which construct 

 these coral rocks are never found living at a 



Madrepore Coral (Madrepora 

 plantaginea). 



greater depth than 

 1 80 feet, so that, 

 when the reef is 

 thicker than that, 

 either some subsid- 

 ence or some up- 

 heavalhastaken place 

 with the rock on 

 which the coral struc- 

 ture rests. This kind 

 of coral is sometimes 

 used as a building- 

 stone, and in the pre- 

 paration of lime. 



The beautiful sub- 

 stance red coral is 

 the calcareous axis of 



the compound zoo- 



phite, Corallium ru- 



t>rutn,a.nd is obtained 



almost entirely from 



the Mediterranean. The principal fisheries are on 



the African coasts, and at present it is the Italians 



and Maltese who are 



chiefly engaged in it 



Nets and iron drags 



are used in obtaining 



the coral, which is often 



brought up from depths 



reaching to about 800 



feet From at least 



Pliny's time to the 



present day, the great 



market for coral has 



been India and other 



Eastern countries, 



where it is held in 



great estimation by 



the natives for orna- 

 ments of various kinds. 

 Even their dead are Coral, shewing the polypes 



frequently adorned with ( Corallium rubrum). 

 coral, to preserve them 



from evil spirits. The Romans used this material 



