a Leather-like Substance composed of Infusoria. 321 



and the gas then given off conducted into a solution of nitrate 

 of mercury, there is no black precipitate, neither are white 

 fumes observable when the gas is brought into contact with a 

 glass rod dipped in acetic acid : consequently no ammonia is 

 formed when the substance is burnt, and, therefore, it can con- 

 tain little or no nitrogen. The ash of itself, or when moistened 

 with sulphuric acid, does not colour the oxidizing flame of the 

 blowpipe. In borax it is dissolved, giving a gloss which while 

 warm is of a deep yellow, when cold of a pale yellow colour. 

 With the double salt phosphate of soda and phosphate of am- 

 monia it gives a pale yellow glass, leaving a thin scale of si- 

 lica. Fused with soda and saltpetre on a platinum plate the 

 ash gives a deep green mass. It has no alkaline action, does 

 not effervesce with .acids, nor does it contain any salt soluble 

 in hot or cold water. 



Thus the ash of the substance in question is composed es- 

 sentially of silica, oxide of manganese and oxide of iron. The 

 substance itself appears to be an aggregation of leaves, from 

 which the green colouring matter, the extractive matter, and 

 also the organic matters have by some organic process entirely 

 disappeared. 



I shall endeavour to find out the circumstances under which 

 this complete discoloration of the ligneous matter of the 

 leaves takes place, for this is interesting in a technical point 

 of view. „ 



Postscript by Prof. Ehrenberg. 



The very meritorious attention of Prof. Kersten to this 

 leather-like substance has recalled to my mind the subject 

 formerly touched upon p. 119 of my work on Infusoria, but 

 particularly so in relation to the meteoric paper of Courland * 

 that I could not omit submitting it to a microscopic exami- 

 nation. With regard to this meadow-leather of Schwarzen- 

 berg, it consists most distinctly of Conferva capillaris, Con- 

 ferva punctalis and Oscillatoria limosa, forming together a 

 compact felt, bleached by the sun on the upper surface, and 

 including some fallen tree leaves and some blades of grass. 

 Among these confervae lie scattered a number of siliceous in- 



* A translation of Dr. Ehrenberg's notice on the meteoric paper of 1686 

 was given at p. 185 of the present volume. — Edit. 



Ann. Nat. Hist. Vol.3. No. 18. July 1839. 2 a 



