Polytechnic Association Proceedings. Y81 



dried, aud then burned in a close retort. In order to make the 

 mixture more porous, common salt or a salt of potash is added, 

 and, after burning, the salt is washed out with water 



METHYLIC ALDEHYDE. 



Dr. Hofmann has succeeded in forming this aldehyde, which was 

 the only one that had not been previously formed from a corres- 

 ponding alcohol. The operation is a very simple one. He passes 

 a mixture of the vapor of common air and the vapor of methylic 

 alcohol or wood spirit {achelat) through a long platinum sph-al, 

 made red hot by a voltaic current, and the desired product is 

 formed. Like common aldehyde, the methylic reduces silver solu- 

 tions, causing a metallic coating of silver to be deposited on the 

 glass, with this difference, the coating is said to be more solid than 

 that produced by other reducing agents. 



BENZOIC ACID FROM NAPHTHALIN. 



Benzoic acid, now largely used in several branches of the indus- 

 trial arts, may be prepared by a new and simple process recently 

 made public by Dr. Vohl. Naphthaline is first changed into naph- 

 tbalic acid by means of sulphuric acid and peroxide of manganese. 

 Naphthalic acid is mixed with a surplus of lime, and exposed to a 

 temperature of from five hundred and ninety-six degrees to six 

 hundred and fifty degrees F., in a perfect vacuum. Benzoate of 

 lime is thus formed, and by distilling the lime compound, benzoyl 

 is produced. Benzoic acid is precipitated from benzoate of lime 

 by means of hydrochloric acid. The best proportions for forming 

 naphthalic acid are twelve parts of pure naphthidine, ninety parts of 

 common sulphuric acid, and eighty parts of peroxide of manganese. 



CURIOUS EXPERIMENTS WITH PROJECTILES. 



M. Melsen's experiments have excited great interest at the French 

 Academy of Sciences. M. Dumas stated that a leaden ball, falling 

 from the height of about one meter into water, drew with it twenty 

 times its volume of air. The same ball projected by powder to 

 the interior of a vertical cylinder filled with water, and closed at 

 both ends by means of plaster diaphragms, carried with it one 

 hundred times its volume of air. When the initial velocity of the 

 ball was small, the hole made in the plaster was about the same as 

 the diameter of the ball, but when the velocity was greatly 

 increased, the size of the hole was excessively large, and a double 

 border was formed around the holes where the ball entered and 

 passed out of the cylinder. The cause of the increase of the size 



