230 



Dr. Jackson exhibited a glazed, earthen bowl, present- 

 ing, upon its internal surface, efflorescences from the 

 cracks in the glaze, of irregular forms of Bichromate of 

 Potash. 



A saturated solution of the .Bichromate of Potash had been 

 standing for some time in the bowl, and it was afterwards washed 

 out clean, with boiling water. A solution of Alum was then 

 introduced, which, entering the pores of the Earthenware, 

 already saturated with the Bichromate, forced out these peculiar 

 efflorescent crystals. 



This phenomenon is well known to chemists and mineralo- 

 gists under the name of Ludus Helmonti. It is seen in concre- 

 tions in cavities of rocks, and has often been supposed to be of 

 organic nature, but is really owing to a shrinkage of the rock, 

 and an oozing of crystals from the pores. The fibrous Selenite, 

 or Flowers of Gypsum, of the Mammoth Cave ; the filamen- 

 tary or capillary Silver and Copper in crevices of the igneous 

 rocks ; the exudation from the shrinking slag in copper works, 

 and the formation of fibrous ice in crevices in clay, so often 

 seen by the road side, are familiar illustrations, originating from 

 similar causes. 



Dr. Jackson presented specimens of Argentiferous Galena ; 

 Crystallized Tremolite, containing Copper Pyrites, and Iron 

 Pyrites mixed ; Crystallized Tremolite, containing Galena ; and 

 Zinc Blende and Argentiferous Galena ; from Warren, N. H. 

 Dr. Jackson gave an account of this mine, and explained the pro- 

 cesses of mining by shafts, levels, and right and inverted grades. 



Dr. A. A. Hayes exhibited specimens of Native Iron from 

 Liberia ; and gave the historical and chemical evidence of its 

 having been in use many years by the natives. By the simple 

 process of hammering, this iron has been converted into rude 

 instruments. It contains one and a half per cent, of crystals of 

 Quartz and magnetic oxide of iron, and,' consequently has never 

 been heated or wrought. There is no trace of Carbon or Man- 

 ganese, or Nickel, which, by their presence, would show it to be 

 meteoric. Dr. Hayes's communication will be given hereafter, 

 in full. 



