POLYMORPHISM AT HIGH PRESSURES. 119 



higher than mine. A linear extrapolation of my points on the II-III 

 line would indicate —36° as the transition temperature at atmospheric 

 pressure, and the probable curvature of this line would bring it down 

 to somewhat below —40°. The discrepancy may possibly be due to 

 still another modification, with a triple point on the line II-III below 

 0°. My point corresponding to Wallerant's 97° is at 87°. The dis- 

 crepancy cannot be due to impurity of my specimen, because there 

 was no preliminary roimding whatever of the corners of the isotherms. 

 There is, however, a possible uncertainty of two or three degrees in 

 my value 87°, as may be judged from the irregularity of the points 

 at the lower end. I do not consider that this uncertainty can be 

 possibly large enough to account for the discrepancy. 



Wallerant's paper did not become known to me until all the other 

 transition lines of camphcr except I-II had been investigated. If it 

 had not been for his paper, this transition would have entirely escaped 

 me, because as has been previously explained, only in rare cases have 

 I made especial search at atmospheric pressure for new modifications, 

 but have accepted absence of mention of such transitions as presump- 

 tive evidence that there are none. This example brings out that in 

 exceptional cases, where the transition line is very steep, or the change 

 of volume very small, my method of exploration may possibly leave 

 new transitions undiscovered. Camphor is a particularly unfavorable 

 case, because both the transition line is very steep, and the change of 

 volume very small. 



Potassium Acid Sulfate. — This was obtained from Eimer and 

 Amend, of the "tested purity" grade. Two sets of runs were made; 

 the one gave all the high pressure points, and the other, with the low 

 pressure apparatus, gave two points at nearly atmospheric pressure. 

 Immediately before use it was heated to 100° in vacuum for several 

 hours to remove the moisture. For the high pressure runs it was 

 hammered cold into an open steel shell, and pressure was transmitted 

 directly to it by kerosene. For the low pressure run it was melted 

 into a glass tube, the glass removed, and the specimen placed loose in 

 the pressure chamber, in direct contact with the kerosene. 



KHSO4 has four modifications. The existence of forms other than 

 the ordinary low temperature form does not seem to have been known 

 before, although there are two transition points and three modifica- 

 tions at atmospheric pressure. I was fortunate not to miss altogether 

 the other modifications. At room temperature no new form was found 

 out to 12000 kgm., although a transition line was crossed at 7000 or 

 8000. The reason for this is that at 20° the reaction is very sluggish. 



