390 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



place a lock on the door ? Why not secure it in tlie wall of the building 

 and let the bolt catch into the door ? Then we mig-lit liave the lock aa 

 massive as we please. 



Mr. Butler. — In Egypt they place the locks on the outside of the doors. 

 The locks are made of wood, and travelers speak of seeing men with bun- 

 dles of wooden keys on their shoulders. 



Mr. Fisher. — Would it not be a good measure of security to have the 

 keys so massive that they could not be carried without being seen ? 



Mr, Butler. — That would involve the necessity for a large keyhole, by 

 which powder could be introduced and the lock blown off. This is now 

 the principal danger that we have to guard against. The permutation lock 

 is capable of several hundred millions of changes and cannot be picked, 

 but it may be blown off by gunpowder. To prevent this, bank locks are 

 now made with vents or, openings for the gas to escape, and this is gene- 

 rally a safeguard against the effects of powder, but I suppose it might not 

 be against gun cotton, as that explodes more quickly than gunpowder. 



The Secretary called on Mr. Butler to exhibit and explain in this connec- 

 tion the key of the lock manufactured by him for street doors, which was 

 done. 



The key is about as large, both in thickness and area, as a quarter of a 

 dollar, and works in a slot in the metal plate in the front of the door, only 

 about one-sixteenth inch thick. This is for street doors and common doors 

 of any kind. Bank directors are now most partial to what are called com- 

 bination locks, which have no key-hole and will of course admit no powder. 

 They are operated by adjusting disks or the like on the face of the lock. 



Gun cotton, or ftdminates, which act quicker than gunpowder, it was 

 thought would be more destructive in a lock, but Mr. B was not aware that 

 they had been actually used b}^ burglars, though he believed there was 

 always danger that they would be. 



Mr. Dibben exhibited a model of Mr. John Tremper's automatic cut-off 

 mechanism for steam engines. Its great feature is its quickness of action. 

 The valve is a ring, and drops into another ring so as to cut off the steam 

 without slamming upon any seat, and needs no dash put to soften the 

 blow, like most of such drop cut-offs. 



The Chairman. — Will Prof. Seely state whether gun cotton explodes 

 more quickly than gunpowder? 



Prof. Seely. — Mr. Chairman, I shall make my remarks with considerable 

 confidence, as I have probably made more gun cotton than any other per- 

 son in America, and have tried mcn-e experiments upon it. If a bunch of 

 gun cotton, pulled out loosely, is laid upon a hot stove, and some gun- 

 powder is laid by the side of it, probably three-quarters of the persons in 

 the room would say that the gun cotton explodes the more quickly. If 

 some gun cotton is pulled out loosely, and some powder is sprinkled on it 

 and a match is applied to it, the cotton will burn without setting the pow- 

 der on fire. This is owing to the fact of its burning with a flame in which 

 the heat is not intense. If some gun cotton is placed loosely in a wide- 

 mouthed vial, and is lighted at the top, it will burn prett}' quickly at the 

 top, but the combustion will proceed more and more slowly till about three- 

 fourths of the mass is burned, when it will go out. If gun cotton is twisted 



