1821.] Solution and Crystallization of Lime, 109 



the access of carbonic acid from the atmosphere. In a very- 

 short time, small white particles were deposited in the lime water,, 

 and after about two ounces of the water had been evaporated, L 1 

 discontinued the ebuUition, and cooled the lime water secured 

 from atmospheric air. 



On examining the particles which had been deposited, it was 

 evident that they were ciystalhne, although the smallness pre- 

 Tented the determination of their form ; they had nevertheless 

 the usual briUiancy of sahne crystals. 



To determine what quantity of hme had been deposited by crys- 

 tallizing, and what proportion it bore to the evaporation, I decom- 

 posed a pint of the hme water in the mode already described by 

 carbonate of ammonia, the carbonate of lime precipitated wa» 

 dried, and weighed 8*6 grs. = 4*85 grs. of hme. It is, there- 

 fore, evident that the action of the heat had caused the crystalli- 

 zation of the hme, and had effected it in a much greater degree 

 than could be accounted for by the evaporation which occurred^ 

 The lime water before evaporation contained ^-g- of its weight 

 of hme ; after l-13th had been evaporated, the quantity of lime 

 was reduced to y-jVr ■> ^^ ^^^^ more than one half of the lime was 

 crystaUized by evaporating l-13th of the solution. 



The cause of this crystallization appears to me to result from 

 the effect which heat sometimes produces of increasing instead 

 of diminishing the attraction of cohesion. The affinities which 

 are brought into play are, the attraction of aggregation of 

 the particles of the lime for each other, the attraction of the 

 lime to form a hydrate with a small portion of water, and the 

 mutual affinity existing between that hydrate and water of 

 solution. 



Among the cases which may be cited as proving the aggre- 

 gating power of heat is this : If some peracetate of iron be 

 decomposed by ammonia, the oxide is quickly redissolved by 

 acetic acid ; but if the oxide of iron be boiled in the solution 

 from which it is precipitated, the acetic acid is incapable of dis- 

 solving it, on account of the cohesion which the oxide of iron 

 has suffered by heating. 



As crystallization is but a modification of cohesive affinity, we 

 may, I think, consider, that the cohesive or crystalhne affinity ' 

 excited by the heat, increased by the affinity of the hme 

 for a definite portion of water, is so much greater than the affi- 

 nity of the hydrate of lime for the water of solution as to occa- 

 sion crystallization. If the quantity of hme crystallized was in 

 any degree proportional to that of the water evaporated, there 

 would be no occasion to suppose the existence of the cause I ^ 

 have mentioned. 



Mr. Dalton, instead of merely heating hme water, which had 

 been prepared at a lower temperature, boiled it again with hydrate 

 of hme ; it is evident, therefore, that the crystallization which he 

 would otherwise have observed could oiiot be adduced to account 



