Holmesdale Natural History Club. 



if, on the other hand, the plaster is under-baked, it sets too quickly, and 

 then becomes soft. Plaster readily absorbs damp, and requires to be kept 

 in a dry place. Broken plaster casts, &:c., if subjected to heat to drive oS 

 the water, may be again converted into plaster of Paris, and used afresh, 

 but it does not set so hard as fresh plaster. This process may be repeated 

 two or three tim^es, but on each occasion it loses much of its vitality. Good 

 plaster should give out a sensible heat in setting. After baking, the stone 

 is extracted from the bottom of the kilns, repeatedly tested, and then 

 wheeled to the mill-house. At the mill the baked gypsum is passed through 

 a second set of crushers, and descends to the stones, and after being ground 

 the plaster is elevated to a sieve-floor, where it passes through rotating 

 boxes formed with fine wire panels. It has now become plaster of Paris, 

 and is conducted down deal boxes or pipes to the ground-floor ; here it falls 

 into sacks attached to the pipes, and is then weighed into quantities of 

 2 cwt., and wheeled into the railway trucks in a covered siding running 

 along one side of the mill-house. I have briefly described the process of 

 winning the gypsum and its manufacture, and have now only to glance at 

 the purposes to which it is ai^plied. The bulk of the plaster sold is used 

 for cornices and enrichments of ceilings, and for plastering walls or parti- 

 tions where time is an object, owing to its rapid setting qualities. The finer 

 kinds are used for statues, busts, &c.,and I regret to say, as has been shown 

 by our police trials, for adulteration of flour ; but we must hope this is an 

 exceptional case. The material in this instance came from Antwerp. 

 Plaster, when burnt so as to lose its setting property, is used to thicken and 

 whiten paper, &c., also as a dressing for calicoes. From its exjoansion 

 in setting, plaster is a very valuable material for making moulds to repro- 

 duce medals and coins, as it gives a very sharp cast. Coiners are well 

 aware of this fact, and use it for their moulds. Ground unbaked gypsum 

 is a valuable manure from its great affinity for ammonia ; a thin layer of 

 the raw powder laid on stable or other manure entirely fixes the ammonia. 

 The lime, too, acts as a manure in most soils. Liebig speaks verj- favour- 

 ably of it as a manure, especially for clover, beans, peas, and other leo-u- 

 minous plants. At Betchworth one half of a field was dressed with gypsum, 

 and the straw was 50 per cent, in excess of the other half where none was 

 used, and the ears were much larger. A vast number of articles more or 

 less ornamental are made from the Derbyshira gypsum, as vases, candle- 

 sticks, boxes, watch-stands, paper-weights, &c. A large export trade is 

 done with America in these articles. The excellent quahties of Bass'e and 

 Allsopp's ales are stated to be partly due to the water, which is derived 

 from a g}rpseous stratum. Broken or pounded gypsum is used by some 

 brewers to harden the liquor. The large amount of sulphuric acid (46-31) 

 present in gj'psum has suggested the manufacture of that acid from gypsum, 

 but although several attempts have been made to extract the acid, it has, 

 I believe, up to the present time not been done so as to be a financial suc- 

 cess. Pure gypsum or alabaster has been much used for tombs and monu- 

 ments in our cathedrals and churches, particularly during the reigns of 



