146 BRIDGMAN. 



simple salts, as suspected for KoZn (804)2. The apparent irreversi- 

 bility may be simply an effect of diffusion, which must be very slow 

 at high pressures. 



Potassium Binoxalate. — This was obtained from Eimer and 

 Amend. It was hammered cold into the open steel shell, and pressure 

 transmitted directly to it by kerosene. It crystallizes with one mole- 

 cule of water. This, like (NH4)2KPOi, is a substance with a new 

 modification in a region where it is chemically unstable, so that it was 

 not possible to more than establish the existence of the transition. 

 The instability is greater than that of (NH4)2KP04. At room tempera- 

 ture no transition was found to 12000. At 100°, there is a transition 

 at about SOOO kgm., with a change of volume of about 0.0009 cm.^ 

 per gm. This transition was verified by repetition. Presumably it 

 is of the ice type. On setting up the apparatus again, no transition 

 could be found at 100°, nor yet at 200°. On cooling and opening the 

 apparatus there was an almost explosive evolution of gas, and the 

 substance was found completely decomposed. For some reason the de- 

 composition must have taken place at a temperature lower than 100° 

 on the second run. 



General Survey of all Substances Examined. 



The purpose of this section is two-fold. It is, first, to give a list of 

 all those substances among which I have made unsuccessful search for 

 other modifications. Information of this sort is doubtless of value, 

 but too much weight must not be attached to it because failure to 

 find a new form does not prove that none is capable of existence — the 

 frictional resistance to the transition may be too great to allow it to 

 start. In the second place, the purpose is to give some idea of the 

 nature of the clues that I have followed in the attempt to coordinate 

 the various data and to find some method of predicting whether a 

 given substance is likely to have new polymorphic forms. This 

 purpose will be served by grouping the various substances according 

 to the clue that suggested their investigation. This purpose will also 

 be furthered by including in the groups the substances which do have 

 new forms and the data for which I have already published. The 

 following contains, therefore, a collection by groups of all the sub- 

 stances that I have investigated either for melting or polymorphic 

 forms. Of course for those substances whose melting curves have 

 been measured, the range over which search for poh'morphic forms 



