32 HOW — ON MINERALOar OF NOVA SCOTIA. 



lime and magnesia, and other ingredients do not interfere witli 



their use as manure, but prevent their affording the best plaster. 



An opinion prevails that "rotten plaster" or that which has 



been exposed to the weather and crumbled down has lost its 



*' strength". I analysed such a gypsum from the property of 



O. King, Esq., of Windsor, and found it to contain — 



Water and trace of carbonic acid, 21.16 



Lime, 33.02 



Sulphuric Acid, 45.99 



100.17 

 or almost exactly the quantities of ingredients proper to pure 

 gypsum : hence the rock Avas entirely unchanged, chemically, 

 by exposure, and fit for all the purposes to which it can be 

 applied. TJnweathered gypsum varies very much in hardness 

 but is never so hard as anhydrite, which is called from obvious 

 property, " hard plaster." 

 Anhydrite is composed of — 



Lime, 41.18 



Sulphuric acid, 58.82 



100.00 

 it is of various colours, as dark blue, grey, and purple : exposed 

 to the weather it becomes white with a j)eculiarly rough surface, 

 hence it is often called in this condition " sharkstone." It 

 varies much in hardness, some samples give a clear sharp sound 

 under the hammer, others sound dull ; hard plaster is often a 

 mixture of anhydrite and gypsum, and affords some water on 

 being heated. It is used at Windsor as a building stone for the 

 foundations of houses, and walls to support fences. It makes 

 apparently a good substitute for marble in in-door work ; a small 

 table-top and a pedestal were made and polished at Windsor, 

 by Mr. Wood, and shewn at the last Paris Exhibition ; the 

 latter especially was much admired at the preliminary Exhibi- 

 tion in Halifax. How loug the beauty of surface will be re- 

 tained remains to be seen ; since blocks of almost any useful 

 dimensions can be obtained a trial of its qualities is well worth 

 making, and a very suitable place for the experiment is the 



