1883.] NATURAL SCIENCES OF PHILADELPHIA. 75 



senting the appearance of being withered or dead. Tliey expand 

 again in a few da3's of temperature above the freezing point. 

 Specimens of this Sedum, and of Opuntia Missouriensis^ preserved 

 just above freezing point under glass, did not shrivel — and a plant 

 of Echinocactus Simpsoni. taken under cover, after the mammae 

 had been appressed b}' frost, expanded them to its summer con- 

 dition in a short time afterwards. 



Assuming from these facts that the liquids in plants which are 

 known to endure frost without injury, did not congeal, it might be 

 a question as to whnt power they owed this successful resistance. 

 It was [)robably a vital power, for the sap of plants, after it was 

 drawn from the tree, congealed easily. In the large maple tree 

 already referred to, the juice not solidified in the tree, exudes 

 from the wounded portions of branches and then freezes, hanging 

 as icicles ofteu six inches long from the trees. 



March 20> 

 The President, Dr. Leidy, in the chair. 

 Twenty -eight persons present. 



Note on a New Gold-purple -Dr. George A. Konig stated that 



while experimenting with a solution containing 



Ca,HiAs,0, . . . = 5-242 



CaSO, 



CaCl, 



MgCl, 



AuCl, 



H.AsO, 



= 2-983 

 = 4-890 

 = 2-736 

 = 0-112 

 = 10-290 



26-1 63 grains per liter, 

 he observed that upon adding to it very slowly a solution of 

 one part of crystallized ferrous sulphate in ten parts of water, 

 stirring vigorously after each drop, at first a white turbidity 

 formed which gradually assumed a ver}^ rich purple color. The 

 fiocculent precipitate settles completely in twenty-four hours, but 

 may be collected on a filter at once. Sometimes the purple color 

 develops gradually, requiring several hours, the precipitate being 

 whife for some time. This result obtains, when less ferrous salt 

 is added than required. One cub. cent., containing yj^ milligr. of 

 gold, of the above solution with yV cub. cent, of ferrous solution, 

 developed a very fine precipitate. Sometimes the purple does 

 not develop at all ; the precipitate turns bluish gray and 

 remains so. 



This purple substance can be dried at 100° C. without change of 

 color. Heated to red heat the pieces assume a glazed appearance 

 and turn black ; but the fine powder again shows a blue-purple 



