214 PHYSIOLOGICAL BOTANY. 



nothing but globules, and what proves them to be in a 

 fluid state, is that they are frequently seen to run into 

 one another. The crystal is then suddenly formed ; in 

 the above instance, it is a rhombohedron or crystal of 

 Arragonite, according to the temperature. Schleiden has 

 not seen this, and is unacquainted with my little work, * On 

 the Formation of Solid Bodies/ Berlin, 1841. My friends 

 H. and G. Rose and Poggendorf have seen it. But 

 further : "At first it is natural, that if we desire to 

 observe the formation of crystals, precipitation should 

 not be selected for the purpose, which chemists consider 

 to belong to the so-called irregular form of crystallization, 

 but that the observations should be made at first upon 

 simple crystals whilst separating from concentrated liquids. 

 In this way we observe in each case, as e. g. with nitres, 

 ammonio-chloride of platinum, and most beautifully and 

 readily with the ammonio-chloride of zinc, &c., that the 

 nuclear crystal suddenly springs up, not at any given 

 moment, in the liquid which was previously perfectly 

 clear, and which remains so, and then whilst apparently 

 at perfect rest, is seen gradually to increase in almost 

 imperceptible starts by external deposition." If some 

 chemists consider precipitation as only irregular crystalli- 

 zation, they have done wrong. The above means of 

 making the observations are totally impracticable. If the 

 concentrated solution be allowed to evaporate slowly, the 

 formation of the crystals can only be observed with great 

 difficulty ; if it be allowed to cool suddenly, the crystals 

 are formed so suddenly and in such numbers, that indi- 

 vidual crystals are difficult to trace. Precipitates which 

 crystallize slowly are the best to examine, as e. g. carbonate 

 of lime, very little of which must be placed under the mi- 

 croscope. In precipitates which crystallize rapidly, as sul- 

 phate of lime, the first stage of globules cannot always be 

 perceived, as the crystallization ensues too rapidly ; some- 

 times, however, for this very reason, the phenomenon is 

 seen with surprising distinctness." Further : " If, how- 

 ever, two liquids which yield a single precipitate be mixed 



