MECHANICS AND USEFUL ARTS. 81 



takes place, it is almost impossible, by the existing modes of 

 amalgamation, to recover the minute particles which float otf 

 with the currents of water, and ai-e lost. The action of the sodium 

 in recovering the mercury which has passed into this condition is, 

 perliaps, its most remarkable property. — Mining Journal, 18G6. 



SODIUM AMALGAM. 



This is now likely to be superseded by a far less expensive, and, 

 it appears, not less useful material. Caustic soda has not only 

 been found quite as effective as sodium amalgam, but it is contested 

 that the sodium in the amalgam actually assumes the form of 

 caustic soda before producing its ett'ect. A very simple experi- 

 ment will show the efficiency of the soda. If a finely pulverized 

 metallic powder is thrown into water, no amount of stirring will 

 cause it to fall to the bottom of the vessel ; it is rendered specifi- 

 cally lighter than the fluid by the coating of air which adheres to 

 it. But if a very small quantity of caustic soda or potash is added, 

 it will soon descend from the surface to the bottom. It is sup- 

 posed that the minute particles of mercury also, and of gold, are 

 prevented from coming into contact by a coating of air, which the 

 alkali removes in a way not yet ascertained. The jjotash or soda 

 must not be allowed to lose its causticity by exposure to the air, 

 or it will be ineflTective, having become a carbonate. — Intellectual 

 Observer, Sept., 1866. 



SIMPLE MODE OF MANUFACTURING SULPHURIC ACID. 



The necessity for large and costly leaden chambers has rendered 

 the manufacture of sulphuric acid both troublesome and expen- 

 sive. A method of producing it, in which the use of leaden 

 chambers is dispensed with, not only greatly facilitates the jjro- 

 cess, but affords a product which possesses the important advan- 

 tage of being altogether free from contamination by lead. Should 

 it be found to answer for industrial purposes, it will constitute a 

 very important improvement on the method so long in use. It 

 consists in transmitting the acid fumes, formed in the ordinary 

 way, through a series of earthenware cylinders, which are piled 

 up and arranged in such a way as to form a number of columns, 

 filled with coke, and communicating with one anotlier. Straw is 

 introduced into them as required ; and the acid vapors being con- 

 densed by the coke, they trickle down into a reservoir placed 

 beneath for the pm-pose of receiving them. The acid liquid thus 

 obtained is concentrated in the usual way. 



NEW SAFETY LIGHT FOR COAL MINES. 



MM. Dumas and Benoit have been making some experiments 

 in the French collieries on the application of electricity as an 

 illuminating power in " fiery" coal mines. Voltaic electricity has 

 been proposed on several occasions, as a means of giving light to 



