PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 607 



funiace with every volume of oxygen four volumes of inert nitrogen. 

 When cold air is used, part of the heat generated by oxygen is 

 wasted in heating the nitrogen; it has therefore been found highly 

 advantageous to apply the waste heat of the furnace in raising the 

 temperature of the air which feeds the flame, thus forming what 

 is technically called the liot blast. The use of pure oxygen is not 

 economical, but where a very high temperature is required, it is 

 indispensable. In Deville's furnace, platinum, the most refractory 

 of the elements, when placed upon a bed of lime and subjected to 

 the flame is easily melted. About one cubic foot of coal gas and 

 one of oxygen will reduce one pound of platinum. The tempera- 

 ture irenerated in the Deville furnace has been estimated to be over 

 14,000 degrees Fahrenheit, or about five times higher than that 

 required to melt cast iron. 



Carbonate of Soda. 



A new process for producing this important salt has been 

 patented in Great Britain by Mr. Walter Weldon. It consists in 

 placing within a strong vessel equal equivalents of common salt 

 {sodamad) and carbonate of magnesia {jinagmarit), with a small 

 quantity of water, and pumping into the vessel carbonic acid, 

 formed by passing atmospheric air over ignited coal. The car- 

 bonate thus becomes the bicarbonate of magnesia, which dissolves 

 in water and thus decomposes the chloride of sodium. The 

 chlorine unites with magnesium, forming cliloride of magnesium 

 {inagamad)^ at the same time bicarbonate of soda (sodmarit) is 

 formed and precipitated. The whole process lasts but a quarter 

 of an hour. A moderate heat drives off the second atom of car- 

 bonic acid, thus changino; the bicarbonate into carbonate of soda 

 {sodemarit). By evaporating the solution of chloride of magnesium 

 to dryness, and raising it nearly to a red heat, the chlorine is 

 driven ofli" and magnesia is formed. 



America now imports every year several million dollars worth 

 of carbonate of soda from England, where it is made by the use 

 of common salt, sulphuric acid and chalk, according to the pro- 

 cess of Leblance, invented toward the end of the last century. 



Calcutta Copal Resins. 

 The ComjjtesHendus contains some new researches by H. Violctte 

 on those resins, which previously had been found soluljle in ether, 

 turpentine, benzole, petroleum and other hydro carbons, as well 



