, rf >? on the Porosity of Bodies, ;;?? Ml d7Sk 



extremely delicate spangles, which show the same porosity as 

 the finest metallic scrapings obtained by the first-mentioned 

 method. Now as the particles loosened by gentle tapping perfectly 

 correspond in their minutest structure with that of the detritus 

 procured by scraping, they serve at the same time as a proof 

 that the porosity of the finest scrapings is by no means artificial, 

 effected through the operation of scraping, but that it is a natural 

 formation. Further, through the tapping method porous spangles 

 are loosened, not only from the surface of the object, but also (if 

 one cuts it up into points and separates the latter) from its inner 

 parts, and throughout its whole substance, — spangles, the minutest 

 structure of which throughout corresponds with that above de- 

 scribed. It follows hence, that we have here to do with the 

 natural structure of the body itself, and not with an artificial 

 product arisen from mechanical friction and continued tapping, 

 or through the weather. 



There is another advantage in the tapping method. By means 

 of it one is able to perceive with more certainty and ease the 

 structure of all vegetable structures, than by means of scraping ; 

 for as the vegetable structure, generally speaking, is denser and 

 more compact than the structure of animal formations, it is in- 

 comparably more difficult in the former to prepare scrapings fine 

 enough for distinct recognition of the pores. Hence it is well 

 for us to have the method of gentle tapping to resort to. 



2. Method of proceeding with Bodies that are fresh and still moist* 



In animal and vegetable bodies that are fresh and still satu- 

 rated with moisture, may be recognized as well porosity in 

 general as also individual pores. In order to this, pass the 

 knife most gently over their surface, lay the detritus upon glass, 

 and examine without the addition of any water and without a 

 covering of glass. By the latter, a covering of glass, the micro- 

 scopic pores in moist organic substances are not only more or 

 less pressed together, which renders a recognition of them more 

 difficult, but evaporation of the plasma which saturates the 

 texture is retarded and prevented. Now such evaporation being' 

 just what mainly contributes towards a recognition of porosity, 

 the more distinctly does the latter appear the further the evapo- 

 ration has proceeded under the eyes of the observer. In the ex- 

 amination of dried substances these collateral effects of a glass 

 covering are not to be apprehended, as the former sometimes no 

 longer contain any fluids, and sometimes cannot be so easily 

 compressed ; and its application here is usually indispensable in 

 order, as already said, to prevent any confounding with dust- 

 particles which may possibly fall upon the glass during the 

 observation. . . 



