142 BRIDGMAN. 



Sb2S5. At room temperature it shows no transition at all to 12500 

 kgm.; probably the impuritj^ of Sb^Sa is so effectively dissolved in 

 the other components that its transition is suppressed. On raising 

 temperature at 12000 on the orange SboSs a partial decomposition 

 takes place with decrease of volume, and on releasing pressure at 200° 

 the decomposition is completed near 5000 with further decrease of 

 volume. This second point at 5000 was verified by repetition with 

 another sample. On further release of pressm-e to 4000 the melting 

 point of the free sulfur is reached. The end product is free sulfur 

 and black Sb2S3, just as in the previous case. It is curious that the 

 manner of decomposition of the orange Sb2S5 should be more like that 

 of the red SboSs than that of the red S62S5, although the latter doubtless 

 contains a larger proportion of red Sb2S3 than the orange Sb2S5. The 

 most obvious difference between the decomposition of red Sb2S3 and 

 orange Sb2S5 is that with the latter the decrease of volume at 200° 

 occurs at a considerably lower pressure, 5000 against 10000. Probably 

 the explanation is partly to be found in complicated mixed crystal 

 relations. 



No further attempt was made to straighten out the relation of 

 these various sulfides; a complete investigation would be a matter of 

 great difficulty, demanding first of all accurate chemical analysis 

 of the various substances. As such, the subject is beyond the scope 

 of this investigation. 



Double Sulfate of Zinc and Potassium. [K2Zn (804)2]. — This 

 was obtained from Eimer and Amend. Analysis showed Fe, .0004%; 

 Na, none; chloride, none. The salt crystallizes from solution with 

 six molecules of water. In this form it shows no new modification 

 to 12000 kgm. at 20° or 100°. The substance was also examined in 

 the anliydrous condition; the water was removed by heating in 

 vacuum to 140° for 1| hours. The anhydrous salt also has nothing 

 new to 12000 at room temperature, but does have a transition at higher 

 temperatures. The transition is well marked. Figure 28 shows the 

 relation between pressure and temperature. The general order of 

 magnitude of the change of volume is 0.015 cm.^ per gm., but there 

 were various irregularities. Once or twice an appearance was found 

 as of a second small transition like a satellite of the main transition. 

 The curves of volume against pressure at constant temperature present 

 an appearance which one might at first take for the usual rounding in 

 the presence of an impurity, but more careful reading shows not a 

 rounding but a sharp break in the direction of the isothermal above 

 the main transition. This is shown in Figure 29. 



