Miscellaneous. 69 



On the Microscopic Constituents of the Ash of Fossil Coal. 

 13y Professor Ehrenberg. 



At the meeting of the Berlin'Academy of the 25th of October, Prof. 

 Ehrenberg communicated an observation of Dr. Franz Schulz of 

 Eldena, which the latter had addressed to M. v. Humboldt in a letter, 

 in which he describes his method of separating the silica contained 

 in coal so chemically pure as to enable us to recognise the microsco- 

 pical siliceous organisms. " The usual method of burning the 

 coal," Dr. Schulz states, " is attended with an unavoidable vitrifi- 

 cation of the mineral constituents, even when conducted in the 

 slowest and most cautious manner, owing to which their cellular 

 structure is lost. After many fruitless experiments I succeeded in 

 hitting upon a method of incineration, which leaves the silica con- 

 tained in the coal perfectly unaltered. Very instructive preparations 

 are readily obtained (from the already known structural relations of 

 siliceous earth in plants) on moistening grass-halms, ears of grain, 

 Equisetum, Spanish cane, &c., with nitric acid, and afterwards burn- 

 ing them on platinum foil. The nitric acid not only facilitates the 

 combustion of the organic substance, but also prevents the potash 

 combined with the vegetable acid from being converted into carbo- 

 nate of potash before the silica has been heated to such a degree as to 

 be less liable to be acted upon. The greater degree of heat required 

 for the perfect combustion of the coal no longer destroys the cellular 

 form of the silica after nitric acid has prevented the production of 

 carbonate of potash on the first application of heat. An excess of 

 nitric acid has the effect of destroying the connexion of the siliceous 

 cells and acts too powerfully upon them, and should therefore be 

 avoided. 



•• Encouraged by the success of these experiments, I turned my at- 

 tention to coal, it being exceedingly desirable to be enabled to detect 

 remains of organic structure in it. The large quantity of siliceous 

 earth contained in all varieties of coal led me to infer that a judi- 

 cious method of incineration would be attended with good results ; 

 your excellency will be enabled to judge from the preparation at- 

 tached in how far I have succeeded. A piece of coal of about two 

 square inches was broken into twelve pieces of nearly the same size, 

 and then treated with nitric acid in a platinum vessel. The nitric 

 acid being evaporated at a moderate heat, I ignited the residue until 

 no further empyreumatic vapours were given off, treated the resi- 

 due again with nitric acid and repeated the ignition. Thus prepared, 

 the coal was placed in a platinum crucible with a lid perforated in 

 the centre, and air was blown from a gasometer through the aper- 

 ture in the lid, whilst the crucible was kept at a red heat over a 

 spirit-lamp, so that the coal was necessarily slowly consumed. The 

 ash thus obtained had not coked, but formed a brownish powder. 

 Some white splinters occur among this, which appear, on microsco- 

 pical examination to be aggregated siliceous cells arranged in regular 

 succession, of the structure of the prosenchymatous cells of wood." 



Prof. Ehrenberg added, that the importance of a method for ob- 

 taining the organized siliceous parts from the lower strata of the 

 earth with their forms preserved for microscopical observation is ma- 



