122 



an acid liquid in the first tan pit, or by a preliminary treatment 

 called " bating," before putting the hides into the pit. With the 

 exception of the phosphate and superphosphate of lime which it 

 seemed appropriate to mention in connection with other calcium 

 compounds used as fertilisers, we have confined our attention 

 .hitherto to calcium carbonate and substances such as 

 quick lime, slaked lime, calcium carbide, etc., which 

 are made directly or indirectly from the carbonate. 

 There is, however, another natural calcium compound 

 occurring in very large quantities that up to the present has 

 only just been mentioned. It is now time to turn our attention to 

 calcium sulphate. Like the carbonate, it is found in various forms, 

 having special names and used for different purposes. When 

 massive and compact so as to resemble 1 marble in appearance it is 

 called alabaster. This is sometimes white and translucent, some- 

 times veined and is used for ornamental purposes and for 

 statuettes, vases, candlesticks and the like. As it is somewhat 

 soluble in water it is not suited for use in ornamenting the exterior 

 of a building, where it would be subjected to the solvent action of 

 rain, but it can be effectively used for interior decoration. The 

 alabaster box of precious ointment of which we read in the New 

 Testament was probably not made of the material now called 

 alabaster, but of a special kind of marble, to which the name was 

 formerly applied. In a lecture given on April 20th by Mr. 

 Weigall, formerly Inspector-General of Antiquities to the Egyptian 

 Government, the lecturer described an alabaster jar discovered in 

 a Royal Tomb which still contained the liquid put into it 3,500 

 years ago. The report of the lecture does not say in what sense 

 the word alabaster is here used, but probably the jar was of the 

 stalactitic marble just mentioned and not of alabaster in the modern 

 sense. The more commonly occurring varieties of native calcium 

 sulphate are known as M gypsum" and are much used in making 

 Plaster of Paris. This is most useful to the sculptor, the 

 architect, the potter and the surgeon, and for making casts of 

 miscellaneous small articles such as coins and medals, so that it 

 occupies a high place among the calcium compounds used in the 

 service of man. Artificially prepared calcium sulphate, bearing 

 much the same relation to gypsum, that the precipitated chalk 

 used in tooth-powders bears to native chalk, is employed in the 

 preparation of some kinds of paper under the name of pearl- 

 hardening. Fluor spar is another calcium compound occurring 

 as a mineral. Some specimens are colourless and transparent, 

 others beautifully tinted blue, green, yellow, red, etc. Several 

 •colours may occur in different parts of the same specimen. It is 

 not hard enough to take rank as a gem, but is used for making 

 vases and ornaments of various kinds. As it is found in some 

 abundance in Derbyshire it is often known as Derbyshire Spar. 

 Cornwall also furnishes the mineral, and it is there used as a flux 

 In the treatment of copper ores. From it is prepared hydrofluoric 

 acid, distinguished amongst other acids by the unusual property 



