264 CLASSICS OF MODERN SCIENCE 

 stance is not set upon another atom of the same substance, but atoms 

 of water come between ; atoms of water, which are not united with an 

 atom of soHd substance, so as to form a compound atom, as in the 

 water of crystallization, but which exist in some other unknown man- 

 ner between the atoms of solid substance. It is not possible, there- 

 fore, to determine whether that part of the crystal which is first 

 formed must have an angular figure or not. 



An ordinary crystal consists of a number of lamlnse ; when so small 

 as to be but just discernible, it has the form which the whole crystal 

 afterwards exhibits, at least as far as regards the angles; we must 

 therefore suppose that the first layer is formed around a very small 

 corpuscle, which is of the same shape as the subsequent crystal. We 

 will call this the primitive corpuscle. It is doubtful what may be the 

 shape of this corpuscle in the crystals which are capable of imbibition. 

 The first layer, then, is formed around the corpuscle in the way men- 

 tioned; it grows by intussusception, and thus forms a hollow, round 

 or oval vesicle, to the inner surface of which the primitive corpuscle 

 adheres. As all the new molecules that are being deposited may be 

 placed in this layer without any alteration being required in the law 

 which regulates the coalescence of the molecules during crystalliza- 

 tion, we must conclude that it remains the only layer, and becomes 

 greatly expanded, so as to represent all the layers of an ordinary 

 crystal. It is, however, a question whether there may not exist some 

 reasons why several layers can be formed. We can certainly conceive 

 such to be the case. The quantity of the solid substance that must 

 crystallize in a given time, depends upon the concentration of the 

 fluid ; the number of molecules that may, in accordance with the law 

 already mentioned, be deposited in the layer in a given time depends 

 upon the quantity of the solution which can penetrate the membrane 

 by imbibition during that time. If in consequence of the concentra- 

 tion of the fluid there must be more precipitated in the time than can 

 penetrate the membrane, it can only be deposited as a new layer on 

 the outer surface of the vesicle. When this second layer is formed, 

 the new molecules are deposited in it, and it rapidly becomes expanded 

 into a vesicle, on the inner surface of which the first vesicle lies with 

 its primitive corpuscle. The first vesicle now either does not grow at 

 all, or at any rate much more slowly, and then only when the endos- 

 mosis into the cavity of the second vesicle proceeds so rapidly that all 



