328 On the received Equivalents of Potash, Soda, and Silver. 



tion of Frankenheim (Pogg. xl. p. 44?7). He has found that 

 when a saturated solution of pure nitrate of potash is left in 

 small quantity to spontaneous evaporation two sets of crystals 

 are formed ; one in prisms, the other in rhomboids ; the former 

 the common arragonitic form generally assumed by nitrate of 

 potash, the latter that of calc spar, commonly assumed by 

 nitrate of soda. The rhomboidal crystals are microscopic 

 and pass into the prismatic form by friction, by pressure, or 

 by contact with a prismatic crystal, and hence when the salt 

 is crystallized in large masses they entirely disappear*. It 

 may therefore be considered as demonstrated that the nitrates 

 of potash and soda are at once isomorphous and dimorphous, 

 or isodimorphous ; and since the potash and soda replace each 

 other in certain mineral compounds, the alkalies also, perhaps 

 the metallic radicals themselves, may be considered isodimor- 

 phous. 



Whatever change then we adopt in regard to the atomic 

 weight of silver the same must be adopted for potash and 

 soda. If we halve the atom of the former, potash and soda 

 must be represented as dioxides. Kg O and Nag O : and if we 

 consider the united observations of Boussingault on the com- 

 position of the native alloys of gold and silver from South 

 America, and of G. Rose on the crystalline forms of the native 

 metals in a state of comparative purity to be sufficient evi- 

 dence of the isomorphism and replacing powers of gold and 

 silver, we must also halve the received equivalent of the former 

 metal ; or for the four metals in question we must adopt the 

 equivalents 



Gold -—— Totassmm ... -- — 



2 2 



oM 13*5 ^ ,. 2-912^ 



Silver -—— - Soamm — - — f 



of which the former two are the multiples indicated by the 

 researches of Dulong and Petit. 



I leave it to British chemists to judge how far the reasons 

 here stated are sufficient to authorize the introduction of the 

 proposed change. In compiling the second part of my tables 

 of chemical constants it has been necessary to subject many 

 points of this nature to a critical examination ; and if in these 

 tables I should find it necessary to adopt the smaller multiples 

 for the equivalents of the metals above mentioned I am an- 

 xious that the cultivators of chemical science into whose hands 

 they fall may have an opportunity of estimating the united 



[* See Mr. Talbot's Observations, p. 147 of the present volume. — Edit.] 

 t For easy reference I have copied these weights from Turner's Che- 

 mistry. 



