158 MR. H. BAKER ON SOME THIONATES. 



Sodium Dithionaie (Na.^SJD^i'^Aq), — Its sp. gr. at ii°is 

 2" 1 75. Watts says "it crystallizes by spontaneous evapo- 

 ration in large transparent right-rhombic prisms/^ Gmelin 

 gives several measurements ; but they are not sufficient to 

 calculate all the forms from. My measurements show the 

 crystals to be rhombic and the axes to be « : 6 :c=0'gg22 : 

 I '0000 : 0*598 1 . The forms occurring are oqP, P ^, V, P|, 

 QQ Pqq ; and the type is long prismatic, through predomi- 

 nance of 00 P- III these and the following angular mea- 

 surements the interfacial angles are denoted as in Kopp's 

 ' Krystallographie/ viz. : — 



A = the angle of a pyramid, over a vertical edge in the 

 brachy diagonal. 



B=the angle of a pyramid over a vertical edge in the 

 macrodiagonal. 



C = the angle of a pyramid over a lateral edge. 



W = the acute angle in the vertical prism, and the lateral 

 angle in a dome. 



Form. 



P^ 



Poo W 62 9 62 3 62 12 



Silver Dithionate, Ag2,Si06,2Aq, forms according to 

 Watts, right-rhombic prisms, isomorphous with sodium 

 dithionate. Gmelin gives some measurements. I find 

 the axes to be « : A : c=0"9884 : i"0 : 0*581 1, and the 



forms Poo . P. 00 P; 1^5. 00 Poo . 00 Pco ; the type is very 

 short prismatic. 



