456 TKANSACTIONS OF THE AMERICAN INSTITUTE. 



does not affect it. Iron has what is called a passive condition 

 in which it is not affected Avith nitric acid, and may be put into 

 that passive condition by adding a small quantity of manganese. 

 The reason is that the atomic weight of nitrogen is 14, which is 

 just one-half the atomic weight of iron. But this belongs to a 

 department of chemistry not yet fully investigated. It comes 

 under the head of catalysis. 



Mr. Nash stated that the Franklinite ore in New Jersey is not 

 properly a vein, but a diffusion of the Franklinite through the 

 rock. 



Col. Curtis. — Ores appear in deposits, pockets, or veins. If in 

 deposits, you seldom go down one hundred feet before they are 

 exhausted. Most of the zinc ores are in viens. In New Jersey 

 we have gone down about four hundred feet, and the vien seems 

 to widen as we go down. Geologists consider it a wedge vein, 

 running at a pitch of about seventy-five degrees. If so, there is 

 no such thing as exhausting the ore. 



Mr. Nash argued that it was merely a stratum upheaved so as 

 to lie at that angle. 



The Chairman stated the geographical and geological position 

 of the New Jersey Franklinite ore. It lies between w^alls of 

 limestone, from which it cleaves as readily as if it were acci- 

 dentally pressed in there, and the limestone wall is left clean. 



Subjects for discussion. — The subjects of " Soluble Glass" and 

 of " Explosive missiles of war," were selected for discussion at 

 the next meeting. 



Adjourned to Wednesday next. 



American Institute, Polytechnic Association, ? 



December 4i, 1861. ) 

 Prof. Cyrus Mason in the chair. 



screw steamers. 

 Mr. Fisher contributed to the inventions of the Association 

 according to the plan previously suggested by hira, a drawing of 

 a screw steamer with two advantages ; first, the rudder is placed 

 under the bow, and is balanced, so that it will be more effective 

 and require less power to control it ; second, the screw is lowered 

 and made of larger diameter, so that the whole power of the 

 engine may be applied to the screw, and no paddle wheels will be 

 required. 



