72 ANNUAL OF SCIENTIFIC DISCOVERY. 



Magnesia, obtained by calcination of the chloride prepared by 

 treatment of sea-water, though its hydraulicity is partially de- 

 stroyed by calcining at a white heat, exhibits remarkable hy- 

 draulic qualities when brought to a red heat. Equal parts of 

 chalk or marble and magnesia formed into a plastic mass, be- 

 come hydrated and extremely hard when acted upon by water. 

 A paste made from dolomite, calcined below a red heat and pow- 

 dered, forms, under water, a stone of extraordinary hardness. 



The experiments of M. Deville show that to the hydraulicity of 

 magnesia is due the union of the particles of chalk or marble in 

 forming a compact, homogeneous stone, and numerous obvious 

 applications of this property of magnesia in the arts will readily 

 suggest themselves. 



M. Fremy, in his published researches on hydraulic cements, 

 attributes the setting of hydraulic lime, first, to the hydration of 

 the aluminate of lime, and, second, to the reaction of the hydrate 

 of lime upon the silicate of lime, and the silicates of alumina and 

 lime. 



It is evident from these observations that the oxychloridc of 

 magnesium is a cement of great power and durability, and that 

 as an hydraulic cement it ranks among the best known to modern 

 science. Its application to artificial stone manufacture, we think, 

 solves the problem of how to make such stones of proper density, 

 durability, strength, and capability of taking a high polish. If 

 we may credit the statements in regard to cost of manufacture, 

 there seems no reason why stones of this kind should not be able 

 to more than compete with cut stones of any variety and for any 

 purpose. Scientific American. 



THE DARIEN CANAL SURVEY. 



The United States government expedition sent to survey the 

 Darien Isthmus has returned. Owing to unavoidable causes the 

 expedition did not reach the Isthmus till about April 1. They 

 immediately landed at Caledonia Bay and made a careful explo- 

 ration of the route proposed by Dr. Cullen. They found the 

 lowest mountain pass to be over 600 feet above the sea level. About 

 the first of May the party proceeded to explore the San Bias route 

 from Mandinga Bay, on the Atlantic, to Chepo, at the southern 

 end of Panama Bay, on the Pacific. This route, Com. Selfridge 

 thinks, is available. Tire rainy season commenced before he 

 landed at San Bias, and all the country was flooded with water, 

 yet from his reconnoissance he thinks that a careful survey will 

 develop a route whereby a canal can be made with only 27 miles 

 of cutting. We are pleased to see that he is already ordered to 

 reorganize his expedition for a renewal of the survey next winter. 

 The route favored by Com. Selfridge is the narrowest point of the 

 Avhole Isthmus. It is said that the tidal waters of the two oceans 

 there come regularly within 7 miles of each other, and it is there 

 that the tradition exists that the Indians and buccaneers drew their 

 canoes across. It was there, too, that Vasco Nunez di Balboa 

 lauded, and journeying toward the Pacific first saw the waters of 



