FORMATIVE INFLUENCES 579 



FOEMATIVE INFLUENCES 



By t>ROFESSOR G. J. PEIRCE 



LELAND STANFORD JR. UNIVERSITY 



WHEN I was a boy in New England it was the fashion to decorate 

 the windows of the drug-stores with masses of huge deep blue 

 crystals of copper sulphate — blue-vitrol or blue-stone. These orna- 

 ments have vanished now, even from the country drug-stores. Their 

 places are taken by electrical toys, patent medicines, even animals. 

 But these lumps of translucent crystals always interested me. Their 

 composition is simple; sulphate of copper and water are their sole 

 constituents. The sulphate of copper is itself a dull gray powder, not 

 a crystalline substance at all; but if water is with it, it becomes blue, 

 colors its solutions blue, and crystallizes in very regular form. The 

 color and the form of these crystals depend, therefore, upon both water 

 and copper sulphate. 



The boy who plays with blue-stone, dissolving it in water and 

 then recovering it again by crystallization, thus doing for fun what 

 the freshman in a chemical laboratory does because he is directed, 

 learns that the crystals will be large or small, few or many, according 

 to the speed with which they form; large and few if they form slowly, 

 small and numerous if they form rapidly. This is equally true of 

 sugar, common salt and other crystalline substances. We see, then, 

 that circumstances as well as substance have to be taken into account. 

 Although we can not have crystals of this particular kind unless we 

 have the sulphate of copper, neither can we have them, even with an 

 abundance of the salt, unless we have water also. The water must not 

 be in excess, lest the copper salt remain in solution; nor deficient, 

 lest it remain amorphous. It must be exactly proportioned in quan- 

 tity if the salt is to arrange itself into bodies of definite form. The 

 size and the number of these bodies depend upon temperature, dryness 

 of air, any circumstance, in fact, which influences the rate at which 

 water evaporates from the solution. 



Although the number, size and even the formation of blue-stone 

 crystals depend upon circumstances, and will vary according to cir- 

 cumstances, circumstances can not make blue-stone crystals exactly 

 like the crystals of other things. The crystals of common salt have 

 characters which identify them to the eye and mind of the crystallog- 

 rapher. These characters, we say, are inherent in the substance 

 itself. This may be true actually as it certainly is true practically; 

 but a scientific man might be found who would hazard the opinion 

 that common salt, which crystallizes in square plates with hollowed 

 surfaces under the conditions which we know, might crystallize in 



