J. P. Cooke on Fartrates of Cesia and Rubidia. 73 
No other probable parameters of these planes would even ap- 
proximatively satisfy these values. The crystals represented by 
fig. 3 differ materially from those represented by fig. 4, and were 
obtained by a different crystallization. All of the first have the 
planes +-1, which could not be detected on those of the last. On 
three separate crystals of the form fig. 3, the angle +1 on I meas- 
ured 189° 15’, the same as on the crystals of the first type. 
It is evident, then, from this examination that the bitartrate 
of cesia forms two different types of crystals, which present 
respectively a right-handed and Jeft-handed hemihedrism. Either 
acid was used in the preparation of the salt: 
2. Bitartrate of Rubidia, HO, ,H,O,,.—This salt re- . 
sembles very closely the last, with which it is isomorphous. The 
crystals examined were all similar in character, about 5 milli- 
meters long by 2 millimeters wide, and very perfect. They 
belong to the trimetric system and have the axial relations, 
@.:.b s.e=0°695.: 1 : 0:726 
The planes observed, with the exception of —1, are represented 
on fig. 5, ey are the same as on the last, with the exception 
of the negative sphenoid —43. Of this no trace 5. 
Could be discovered. The planes —1, moreove 
X=108° 40 = Y=2126° 43" - Z=99° 34’ 
Measured. Calculated. 
tI on +1 over vertex, 80° 26/* 
+1 on +1 over it, i itd 
t1 on +1 over iz, 76° 14! 76° 20° 
+1 on I, : 139° 47’ =: 189° 47 
Ton I over a, 71° 83 71° 56/ 
li on 1%, 
Am. Jour. Sct—Srconp Senizs, VoL. XXXVII, No. 109—Jan., 1964. 
10 
