i 



• ^7/-^. 



TJIE BEGINNINGS OF LIFE. 



59 



^"^^"•gJes as tQ, prisms— mixed with a few crystals of calc-spar, because 



the temperature of the solution is lower at first than it 



'dies are 



H 



difFcrenc 



IS 



^ssociatei 



rdncss 

 ^ shall 



J COloiLi 



crystal: 



afterwards becomes/ In other examples we may find 

 not only a striking difference in physical form^ but 

 also a notable change in colour^ occasioned by the new 

 molecular rearrangements which the change of tem- 

 perature seems to necessitate: — ^Protoxide of lead 

 crystallizes after fusion^ as well as from a saturated 

 solution in hot concentrated caustic potash^ in yellow 

 rhombic octahedrons. 



-lepcnd chiefli 



e rormofthec fully saturated with oxide of lead^ so that crystallization 



If, however^ the solution is not 



1 which it 

 ^zes from 



Sep 



m 



does not take place till after complete cooling, red 

 crystalline scales are deposited on the yellow rhombic 



ihedrons^ but octahedrons just formed: if the red crystals are heated, 

 r^ms/ Taking they turn yellow in cooling, in consequence of passing 



at 



^ hot i i^to the first form/ 



cooled, notte 



But in addition to these variations in which a crys- 



itic and rk ^alline form of one kind or another is always present, 

 1 hoi bei ^^ '^^y occasionally find that in saline solutions, solid 



uj, products make their appearance whose outlines 



are 



tly; 



sodium p 



111 



Buence 



rod* 

 oftf 



rounded instead of being bounded by right lines and 



angles. Thus, Dr. Hu 



> 



liar pellicle that forms on the surface of lime-water, 



' Ir a ^ ijj which the crystalline material very closely resembles 



;ontaini"» a layer of tesselated epithelial cells. And lately I have 



dinary tei^P ' seen a somewhat similar crystalline pellicle make its 



niicroscop|^^ appearance on the surface of a solution {m 'vacuo) 



containing small quantities of ammonic sulphate and 



r 



1 



ive 



rhoni 



cvap 



orate 



a 



1 t 



i in s 



iTiall 



sif 



Lancet,' 1863, vol. i. p. 3. 



