by the mutual reaction of Solid Substances. 209 
pestle which had been warmed by hot water were occasionally 
used, care being taken that the heat should not be great enough 
to cause either of the original salts to melt in their water of 
crystallization. 
When two salts capable of metathesis are mixed, chemical 
action apparently begins iar at every point of con- 
tact. But there is a lim the fineness of division which 
may be effected by riechalieat means, and the substance con- 
sists of minute grains coated on the outside with the new pro- 
duct, while remaining unchanged at the interior. 
When liquefaction ensues, the interchange is continued 
either because by removing the particles of the roduct, new 
surfaces are presented, or because the Hae penetrating the 
granules, oe them into their molecu 
If the salts taken furnish little or no vate in excess of that 
required ne conti with the new ones formed, the process of 
interchange apparently soon ceases, unless sufficient heat is 
supplied to fest ally the constituents of the product from as- 
or having the daisies acid ; and altho hits it seems to be che 
exception rather than the rule that there should be liquefac- 
tion in such eases, yet this sometimes occurs. 
Ex. — FeCl, . 6H,0 with Fe,(NO,),. 18H,O liquefied. 
H, oO “e iT “ 
FeCl. . 12 : 
FeCl, . 4H,0* “ “ «“ 
FeSO, . 7H,0 “ “ « 
- “ Fe,Cl, . 6H,O - 
Na,C,H,0,.6H,O “ PbC tio, "°3H,0 2 & 
“ 
NaSO,.10H,O ZnSO, . 71,0 “ 
“ TiSo,.H, “ 
CaCl, . 6H,0 «“ Fe,Cl, . 18H1,0 «“ 
mAh H,O & 
Some interesting experiments oe caustic soda (NaOH 
showed that when it was used with any hydrated sodium salt 
the combined water Min Hislnas evidently to satisfy the 
affinity of NaOH for wa 
KOH was also used vit various hydrated salts, and in 
* Of co a ferric and a ferrous base are not strictly aye same, but ferrous 
nitrate is fi tenable a boty with which to work except in the coldest weather. 
