292 Miss E. M. Walton on Liquefaction and Cold 



for it is sometimes observed that liquefaction seems equally 

 marked, whether the two original salts are mixed or the two 

 bodies formed by their interchange. 



6. The rule among liquids in regard to weak and strong 

 acids and bases seems to prevail with solids also, their action 

 tending to promote or impede liquefaction. 



7. When, by the admixture of two salts, oxidation or reduc- 

 tion can take place, there is again probability of liquefaction. 



j&c.— SnCl 2 . 2 H 2 with HgCl 2 liquefied. 



Fe 2 Cl 6 .12H 2 „ 

 CuCl 2 .2H 2 

 „ „ Pb01 2 no liquefaction. 



In the last iio change by reduction is possible. 



A new Substance. — A notable exception to the rule men- 

 tioned above (that one salt at least should be hydrated), is that 

 of AgN0 3 mixed with HgCl 2 . When these are rubbed together 

 there is decided moistening, which would seem to prove that 

 there is such a body as anhydrous nitrate of mercury liquid at 

 ordinary temperatures. On adding water a large residue of 

 silver chloride is observed. 



Evidences of Chemical Change. — When salts capable of meta- 

 thesis are mixed, in addition to liquefaction, change of colour, 

 formation of an insoluble compound, and escape of a gas are 

 proofs of chemical reaction. 



An important difference sometimes noticed between mix- 

 tures of salts in the solid and the liquid form is the escape, in 

 the former case, of some gas, as C 2 H 4 2 , C0 2 , HC1, or NH 3 . 

 The gas is dissolved by a liquid solution and eludes observation. 



Classification.— -Cases of liquefaction may be divided into 

 two classes — the first including those in which there is mutual 

 exchange of base or acid, the second those in which there is 

 no interchange. 



The mixture of lead nitrate with sodium carbonate is an 

 example of the first class. There is metathesis, and we obtain 

 lead carbonate, sodium nitrate, and ten equivalents of free 

 water. 



Pb(NO 3 ) 2 + Na 2 CO 3 .10H 2 O 



= PbCO 3 + 2NaNO 3 + 10H 2 O. 



Hydrated Product. — When iron nitrate is mixed with cal- 

 cium chloride, thirty-six equivalents of water in some form 

 are obtained. 



Fe 2 (N0 3 ) 6 . 18 H 2 + 3[CaCl 2 . 6 H 2 0] 

 = Fe 2 Cl 6 + 3 Ca (N0 3 ) 2 + 36 H 2 0, 



