242 M. C. Lea — Endo thermic Reactions 



Hallock. But the redaction of the silver haloids and other 

 reactions presently to be described involve a quite different 

 principle. The reactions produced are all endothermic ; en- 

 ergy is consumed in accomplishing them and this energy is 

 supplied by mechanical force. 



The combination of screw and lever affords the best means 

 of applying pressure. A careful study as to the most suitable 

 method of using these powers led to the selection of the vise 

 form. It was found, however, that the manufacturers of 

 heavy vises were unwilling to undertake to furnish vises with 

 jaws that would sustain the force intended to be exerted on 

 them, namely, that of a steel lever three feet long acting on a 

 screw with six turns to the inch. I was therefore obliged to 

 have them made under my own supervision. From a bar of 

 tough rolled iron 4 inches wide by 1-J thick, pieces about 18 

 inches long were cut and were forged into shape by a black- 

 smith ; where the jaws met they were faced with steel welded 

 on. Suitable screws were easily obtained, but the nuts furn- 

 ished with them having commonly only an inch in length 

 would subject the thread to the danger of stripping. They 

 were replaced with nuts 4 inches in length, thus distributing 

 the strain over 24 turns of the thread. Two vises made in 

 this way over a year ago have endured severe use without the 

 least sign of strain. 



With a lever having three feet in length between the 

 center of the screw head and the end at which the force is 

 applied acting on a screw with six turns to the inch, the multi- 

 plication of force is 1357 times. As it is easy to apply a pull 

 of a hundred pounds or even much more, a pressure of 135,000 

 lbs. is easily obtained. As it was intended to keep the sub- 

 stances which were to be subjected to pressure from any con- 

 tact that might affect them they were folded up in platinum 

 foil and this was set in a Y-shaped piece of soft sheet copper. 

 The portion of material which received the pressure was about 

 \ inch long by \ wide ; it consequently had an area of about 

 -J of a square inch. This limited surface received a pressure 

 in the proportion of over a million pounds to the square inch 

 or about seventy thousand atmospheres. These of course are 

 calculated pressures subject to deduction for friction. The 

 amount lost in this way cannot be determined but is known to 

 be considerable. 



By the aid of these means the following results were ob- 

 tained. In all cases the material was wrapped in either plati- 

 num or silver, usually platinum, foil. There was no action in 



