GYPSUM 777 



and obtained a portion for experiment. He reported most favourably as to its utility 

 and value, a result most gratifying to me, as I had received adverse opinions from less 

 experienced persons. This happened, I think, in July 1862: from that time to the 

 present, I have been engaged in investigations how to produce the material cheaply, 

 and how to dry or coagulate it rapidly. In both particulars I believe I have suc- 

 ceeded so far as to warrant the importation of steam-machinery to be applied to its 

 extraction ; and by a fortunate accident I have discovered how to dry or coagulate it, 

 preserving the characteristic of elasticity, at a single operation, by the addition of a 

 simple ingredient not very costly. .... 



' Amongst the useful properties of the Balata, I believe the fresh milk of the bullet- 

 tree to be the best waterproofing material yet discovered. The bullet-tree is a magni- 

 ficent timber-tree, often squaring 30 to 40 inches, and is much used, especially in 

 Berbice, for building purposes. The milk, when quite fresh, is so bland that it is 

 sometimes used as a substitute for cows' milk, and the fruit is delicious.' 



Mr. Ondaatjie, surgeon, forwarded to the same Society, from Ceylon, a specimen of 

 the Alstonia scholaris, which he supposes may be used as a substitute for gutta-percha. 

 The tree abounds with milky juice like the gutta-percha, has a fleshy bark and porous 

 wood, and belongs to the natural order Apocyncce. The natives believe that the tree is 

 poisonous, but Mr. Ondaatjie has proved it not to be so. 



GYIiE. A brewer's vat or utensil. The vinegar-maker's fermented wort. 



GYPSU1K. This natural production, which in its varieties is known as alabaster, 

 selenite, and satin spar, is a sulphate of lime, containing sulphuric acid, 46*51 ; lime, 

 32-56 ; water, 20'93. 



The anhydrite from Derby is a mineral like gypsum, but, as its name indicates, con- 

 taining no water ; its composition being, lime, 41'2 ; sulphuric acid, 58'8 ; this is 

 also called muriacite and tripe-stone. It absorbs moisture and changes to gypsum. 

 When gypsum is carefully burnt, it loses its water of composition, and forms the well- 

 known plaster-qf -Paris. 



The transparent varieties of gypsum are called selenite; its fine massive varieties 

 are alabaster, and its fibrous kinds satin spar. There is another variety in small scales 

 of a pearly lustre, known as Sckaumkalk. 



The fibrous forms of gypsum are cut and polished for small ornamented objects, and 

 are sometimes known as satin spar. 



The gypsum of our own country is found, in apparently inexhaustive quantities, in 

 the Red Marl formation in the neighbourhood of Derby, and has been worked for 

 many centuries. The great bulk of it is used for making plaster-of -Paris, and as a 

 manure ; and it is the basis of many kinds of patented cements, as Keene's, Martin's, 

 and others. 



To get it for these purposes, it is worked by mining underground, and the stone is 

 blasted by gunpowder ; but this shakes it so much as to render it unfit for working into 

 ornaments, &c. ; to procure blocks r for which it is necessary to have an open quarry. 

 By removing the superincumbent marl, and laying bare a large surface of the rock, 

 the alabaster being very irregular in form, and jutting out in several parts, allows of its 

 being sawn out in blocks of considerable size, and comparatively sound (as is illus- 

 trated by the large tazza in the Museum of Practical Geology). This stone, when 

 protected from the action of water, is extremely durable, as may be seen in churches 

 all over the country, where monumental effigies, many centuries old, are now as 

 perfect as the day they were made, excepting of course wilful injuries ; but exposure 

 to rain soon decomposes the stone, and it must be borne in mind that it is perfectly 

 unsuited for garden vases or other out-door work in this country. 



In working, it can be sawn up. into slabs with toothed saws, and for working 

 mouldings and sculptures, fine chisels, rasps, and files are the implements used ; the 

 polishing is performed by rubbing it with pieces of sandstone, of various degrees of 

 fineness, and water until it is quite free from scratches, and then giving a gloss by 

 means of polishing powder (oxide of tin) applied on a piece of cloth, and rubbed 

 with a considerable degree of friction on the stone. This material gives employment 

 in Derby to agood'many hands in forming it into useful and ornamental articles, and 

 is commonly called Derbyshire Spar ; most of the articles are turned in the lathe, and 

 it works something like very hard wood. 



Another kind of gypsum also found in Derbyshire is the fibrous or silky kind ; it 

 occurs in thin beds, from one to six inches in depth, and is crystallised in long needle- 

 like fibres ; being easily worked, susceptible of a high polish, and quite lustrous, it is 

 used for making necklaces, bracelets, brooches, and such like small articles. 



Gypsum is commonly found in this country, in irregular deposits, in the New Eed 

 Marls, especially at Chellaston in Derbyshire, Fauld in Staffordshire, and Newark in 

 Nottinghamshire. A deposit of white crystalline gypsum has been recently discovered 

 in the prosecution of the experimental boring at Netherfield, near Battle in Sussex, 



