338 On Preserving Organic Specimens. 



Art. XIII. — On a New and Effectual Method of Preserving 

 Specimens of Organic Nature, and of obviating the Blanch- 

 ing Influences of Light, and the Depredations of Insects ; — 

 inost Advantageously Applicable to the Formation and Un- 

 liinited Preservation of a Hortus Siccus, or Museum of Dried 

 Plants ; by John L. Riddell, M. D., Professor of Chemistry 

 and Materia Medica, in the Medical College of Louisiana. 



" Corpora non agunt nisi sint soluta." 



It is conceded, I believe, that light exerts an influence in chem- 

 icar changes, by modifying or exacting the inherent electrical en- 

 ergies of material particles. This influence has been observed 

 times innumerable by every one, in the blanching or fading of 

 organic colors. Few, I apprehend, could be found, who would 

 be willing, upon the first proposal, to believe in the possibility of 

 easily and completely averting this fading power of light, and of 

 conferring immutability upon the organic tints which are con- 

 sidered as most delicate and evanescent. 



The possibility of so doing may perhaps be made theoretically 

 to appear, thus : — The particles of an absolutely solid body can 

 suffer no change, because they are inter se immovable. A with- 

 ering leaf, exposed to air and light, fades and decays, because 

 there is moisture present. Liquid water fills myriads of its in- 

 sensible pores and intercellular spaces. The leaf may be dry ex- 

 ternally, — nay, it may be apparently dry within ; yet it is really 

 imbued with more or less of water. This water may give fluid- 

 ity to the fading coloring matter, either by immediate solution, or 

 by becoming impregnated with acid substances. But it is chiefly 

 by absorbing, and thus giving liquidity to oxygen gas from com- 

 mon air, that it contributes to change. Besides, it is favorable to 

 chemical action, by standing ready to dissolve and remove some 

 or all of the eliminated products. Water, moreover, may exert 

 an indirect agency in hastening organic changes, by favoring the 

 existence of insects and animalcules. Light renders the chem- 

 ical aflinities concerned more active, and thereby soon accom- 

 plishes changes which time and other circumstances would ac- 

 complish without it. Those conditions only, on which the 

 power of assuming the liquid state depends, are essential. Re- 

 move them, and no change can occur. 



