10 
temperature to be 1 in 0*994 parts of water. It is remarkable 
that the saturated solution of such a soluble salt should 
boil at so low a temperature. The sp. gr. of the crystals 
of this salt at 13 *5 is 4*536. 
Lead Dithionate. PbS 2 0 6 4Aq. a Is very easily soluble 
in water/' Watts. I find its solubility at 20°*5 to be 1 in 
0*869 parts of water. Its sp. gr. at 11 = is 3 *25 9. 
Calcium Dithionate. CaS 2 0 6 4Aq. The crystals have a 
sp. gr. of 2*176 at 11°. 
Nickel Dithionate. NiS 2 0 G 6Aq. One part of this salt dis- 
solves in 0*897 parts of water at 12°. 
Magnesium Dithionate. MgS 2 0 6 6Aq. According to Watts’ 
Dictionary “forms six-sided tables, very soluble in water; ” 
but Gmelin says it forms ill-defined six-sided prisms. 
I obtained it in oblique prisms ; and found its solubility 
at 17° to be 1 in 0*692 parts of water. 
Sodium Dithionate. Na 2 S 2 0 6 2Aq. Its sp. gr. at 11° is 
2*175. 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 d :b \ c = 0*9922 : 
1*0000:0*5981; the forms occurring are oo P, Px , P, PJ, 
x Px , and the type is long prismatic, through predominance 
of x P. In these and the following angular measurements 
the interfacial angles are denoted as in “Kopp’s Krystal- 
lographie,” 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 
macro ‘diagonal. 
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. 
