430 



merwin: picrate and trithionate 



From two natural prisms (no) A (oio) refractive index 

 measurements gave: 



These values are in line with those of Baumhauer, and give (with 

 the orientation and 2K) data for calculating /3 and 7. That is, 

 /3' = ^ -f 21 to 22 per cent of (7 — (S). Therefore the follow- 

 ing dispersion: 



TABLE I 

 Dispersion of Ammonium Picrate 



Baumhauer's observations on potassium picrate show that it is 

 very like ammonium picrate. The wave-length for which it is 

 uniaxial is evidently shorter than for the ammonium salt. It 

 seems safe to infer that this wave-length is practically that of 

 the hehum green line 502, for which he obtained a single signal 

 when measuring the dispersion of /3 and 7. 



Potassium Trithionate} — -Blades about i cm. long were ob- 

 tained by cooling a hot saturated solution to room temperature. 

 The prism angles of these blades were not normal, but as follows 

 (the dome angle was normal) : 7 crystals, 10 m faces, 23 / faces, 

 10 g faces. 



/ A/ 39° o' — 39° 27' mean = 39° 13' 

 w A m 70 42 — 70 50 mean = 70 46 

 q A g 45 13—45 39 mean = 45 31 



At the base of the blades there were numerous stubby crys- 

 tals, with normal angles. One of these gave the angles 



°3i' 



I A I =39' 

 w A m = 71 3 

 ^ The crystals were prepared and tested by E. T. Ali^En. 



